Ahrens, Wolfgang

Preferred name

Ahrens, Wolfgang

Official Name

Ahrens, Wolfgang

ORCID

0000-0003-3777-570X

GND

137021593

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Use of digital technology to enhance participation in population-based studies for Public Health & Epidemiology
(2026-06-05)
Herrera Espejel, Paula Sofia
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Rach, Stefan
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Brannath, Werner
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Rach, Stefan
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Ahrens, Wolfgang
Advances in digital technologies represent alternative or complementary solution for generating, collecting, storing, processing, and exchanging health information in Public Health and Epidemiological (PHE) research settings. The expanding availability, affordability and accessibility of these tools has enabled the adoption and use of a wide range of hardware, software, and networking services throughout the entire research continuum. Among other capabilities, researchers are now able to collect personal and self-reported health data directly from the research subjects and their own environments. In particular, new information and communication technologies may be practically integrated as part of pre-analytical research stages, such as recruitment and data collection, with the purpose of improving the external and internal validity of sampled data used for statistical analyses and outcome generation. That is, digital technologies are integrated into the routine procedures of population-based studies (e.g., interviewing, invitation and consent material) with the double aim of increasing confidence over findings from available data and increasing the representativeness of such findings to the wider population under study to other settings beyond the study parameters. While these technologies certainly offer promising solutions to the current limitations of procedural stages in population-based research, their use is, however, not without caveats. For example, while technologies such as Machine Translation (MT) may support outreach to certain specific linguistically diverse communities, these technologies might exclude or offer less quality communication services to other specific communities due to differential accuracy across language translations. Moreover, while the availability of online survey technologies offers solutions to increase participation and reduce nonresponse (and, as such, to increase study generalizability and representativeness), these solutions may also generate measurement errors and reduce internal reliability of the data collected. For such reasons, continuous assessments of the technical, socio-economic, and ethical-legal maturity of digital technologies are essential to align their effective and efficient development, adoption and deployment with PHE objectives, such as the World Health Organization (WHO) Essential Public Health Operations. Moreover, the research on their use may also help to clarify their limitations and shed light on their actual potential (e.g., as to not misuse them and further health outcome divides among already disenfranchised communities). Against this background, this dissertation investigates how different digital technologies may serve to increase response in population-based studies from their research onset, namely at the points of initial study invitation and data collection. The cumulative dissertation presents four peer-reviewed manuscripts: three published prior to submission, and one published after, in March 2026. The dissertation addresses the use of digital technology to enhance participation in population-based studies for public health & epidemiology. Section I of the dissertation consists of three introductory chapter. In Chapter One, the dissertation introduces its reader to the current debate on the use of digital technologies in public health and epidemiological research, presenting the working rationale and objectives of each submitted manuscript. In Chapter Two, the dissertation offers an overview of the research concepts, definitions and working frameworks used throughout these manuscripts. Additionally, this chapter offers an overview and mapping of available literature on the use of digital technology throughout ten general research stages for developing population-based studies. Chapter Three summarizes the methods and results of the four submitted manuscripts, while presenting short commentaries and ancillary analyses. Section II presents the four manuscripts submitted as part of the cumulative dissertation. Chapter Four presents a scoping review of peer-reviewed literature published after 2016 on the use of use of MT technologies for disseminating PHE material to specific target audiences in population-based research and surveillance efforts (Herrera-Espejel and Rach 2023). Culturally and linguistically diverse (CALD) populations are often underrepresented in PHE studies. Such underrepresentation may lead to biased study results, limiting their generalizability in practice. Modern MT tools might offer a cost-effective solution to this problem. The review identifies 46 articles addressing the use of MT to facilitate dissemination of public health information to CALD communities. The review indicates that current commercial MT solutions, such as Google Translate and DeepL, may provide sufficiently accurate translations, when used along with pre- and post-editing efforts, namely for non-legally or ethically sensitive materials. As such, the Chapter discusses the limitations of current MT solutions to one-way communication between public health staff and addressed audiences. Questions for future research include: assessing how machine-translated texts are received by different segments of target populations; and understanding the effectiveness of MT for specific two-way communication material, such as participant enrollment, informed consent, and response materials in general. Chapter Five exhibits a cluster randomized control experiment (Herrera-Espejel et al. 2025), which was embedded in the World Health Organization European Childhood Obesity Surveillance Initiative in second-and third-grade classrooms in the cities of Bremen and Bremerhaven, Germany. The study offers an evaluation of the effectiveness of a co-developed physical-digital multilingual outreach solution, namely, flyer with a QR-code linking to multiple language translation of the original study invitation. Based on multilevel mixed-effects logistic regression models, the study measures the extent to which the inclusion of the flyer in the study invitation was positively associated with the response and eventual study participation proportions of linguistically diverse eligible participants, supporting more equitable participation. While the presence of the flyer was associated with increased participation and response of linguistically diverse households from medium-level socioeconomic backgrounds, its effect was not significant for children studying in schools in low- nor high-levels. In view of these results, the study in Chapter Five underscores the importance of tailored approaches to increase engagement among underrepresented communities in population-based health research, as well as the importance of using appropriate statistical methods to investigate the differential outcomes of digitally-based interventions across socio-economic and linguistic subgroups within heterogenous populations. Chapter Six offers an exploratory analysis and evaluation of the effect of using two concurrent interviewing modes on the collection of self-reported symptoms in population-based studies. As was the case of the CoVerlauf study (Rach et al. 2023), two inherently different interviewing modes were used to collect participant data on post-Covid symptoms at their time of infection and interview: Computer-Assisted Website Interviewing and Computer-Assisted Telephone Interviewing. The Chapter explores and discusses the extent of selection effects and measurements effects cause by the use of two modes. The use of the two modes was in itself advantageous to reduce nonresponse, as well broaden the coverage and response of eligible study participants which would have otherwise (e.g., in a single-mode design) not engaged in the study activities. However, due to the inherent characteristics of each mode, the mixed-mode design potentially introduced parallel mode-specific measurement errors, blurring the comparability of items collected through the different information exchange methods at the point of data collection. [This chapter presents the submitted manuscript prior to its publication. The published version is available online (DOI: 10.2196/80631)]. Chapter Seven explores how digital tools might unintentionally increase health inequalities, especially among different socio-economic, gender, and underserved groups. It highlights how the unequal access, use and effectiveness of digital technologies may widen differential health outcomes. The chapter underscores the importance of involving targeted subgroups in the design and development of health interventions to reduce nonresponse or differential response due to the use of digital technology. Section III consists of three conclusive chapters. In Chapter Eight, the dissertation discusses the overall research contributions and limitations for each of the previous chapters. In Chapter Nine, the dissertation offers overall research reflections after completion of the writing of the manuscripts included. Specifically, the dissertation shares final reflections on the importance of linguistic inclusiveness and fairness in PHE participant material (e.g., invitations, consent forms, questionnaires, etc.). It also discusses insights that might be gained from language demographics in Germany based on available data from the Statistische Bundesamt from August 2024, and the foreseeable paradoxes of using digital technology for inclusion. The final Chapter Ten summarizes the overall research conclusions of the dissertation, concluding that, while digital technologies may significantly enhance participation and response in population-based studies, they also risk exacerbating existing inequalities and creating new forms of divides due to limitations in their technological readiness. The dissertation argues that the evaluation and continuous investment in training PHE researchers to understand intersectionality theory and adopt quantitative methods that reflect the superdiversity of populations under study is crucial to improve both generalizability and the reliability of findings in the field. A last section IV organizes the appendixes from Chapter Four, Five and Six.
doctoral thesis
56 33
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Schätzung von Tumorrisiken anhand aus der Berufsbiografie abgeleiteten Expositionsvariablen
(2011-12-13)
Schmeißer, Nils
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Zeeb, Hajo
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Ahrens, Wolfgang
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Ahrens, Wolfgang
Die Identifikation von Krebs verursachenden Expositionen in der Arbeitswelt ist ein Gebiet der Epidemiologie. Dazu werden etablierte Methoden aus anderen Wissenschaftsgebieten integriert. Es wurden die Themen soziale Faktoren und Pestizidexpositionen bearbeitet. Alle Auswertungen basieren auf Fragebogendaten aus Fall-Kontrollstudien. In den Artikeln wurde versucht, das optimale Verfahren zur Einstufung anhand der Anzahl der Exponierten anzuwenden. Alle Risikoschätzer basieren auf logistischer Regression. Potenzielle Confounder wurden in den Modellen berücksichtigt. In Manuskript 2.1 wurde die Assoziation zwischen beruflichen Pestizidexpositionen und Tumoren der extrahepatischen Gallenwege bei Männern in einer multizentrischen Fall- Kontrollstudie untersucht. Expositionen wurden in Bezug auf Zeit, Gebrauch persönlicher Schutzmaßnahmen und Applikationsmethode quantifiziert. Ein publizierter Algorithmus wurde zur Bewertung der Expositionsintensität verwendet. Wenige nichtsignifikant erhöhte Risiken wurden festgestellt, die jeweils auf einer niedrigen Anzahl von Exponierten beruhten. Die Hypothese, dass berufliche Pestizidexpositionen ein Risiko für Tumoren der extrahepatischen Gallenwege bei Männern ist, lässt sich nicht ausschließen. Daten einer in eine Industriekohorte eingebetteten Fall-Kontrollstudie wurden in Manuskript 2.2 ausgewertet, um der Hypothese nachzugehen, dass Pestizidexpositionen und Tätigkeiten in landwirtschaftlichen Berufsfeldern die erhöhte Inzidenz von Keimzelltumoren in dieser Kohorte erklären kann. Es haben 5.3% der Fälle und 6.3% der Kontrollen jemals einem landwirtschaftlichen Beruf ausgeübt. Expositionen gegenüber Pestiziden, Dünge- und Desinfektionsmitteln ergaben keine erhöhten Risiken. Forstarbeit und mit der Verarbeitung von Holz verbundene Expositionen zeigten nichtsignifikant erhöhte Risiken. Es konnten keine Schlüsse über die Assoziation von landwirtschaftlichen Tätigkeiten und Expositionen und Keimzelltumor-risiko gezogen werden. In Manuskript 2.3 werden unterschiedliche berufliche Sozialindikatoren verwendet, um die Assoziation mit Hodentumoren zu untersuchen. Ebenfalls werden Schulbildung und der Ausbildungsstatus untersucht. Ein erhöhtes Risiko konnte nur für Beschäftigungen in landwirtschaftlichen Bereichen anhand des Schemas aufgedeckt werden, das Tätigkeiten ordinal schichtet. Diese Studie legt die Schlussfolgerung nahe, dass soziale Faktoren kein Risikofaktor für Hodentumore sind. Das aufgedeckte erhöhte Risiko für Tätigkeiten im landwirtschaftlichen Bereich kann auf stofflichen Expositionen beruhen. Studie 2.4 untersucht die Assoziation der sozialen Mobilität und Tumoren der oberen Luft und Speisewege anhand der Berufsbiographie. Das Berufspretige wurde anhand des Standard International Occupational Prestige Scale (SIOPS) untersucht. Die SIOPS-Werte wurden in Hoch (H), Mittel (M) und Niedrig (L) kategorisiert. Wechsel zwischen den Kategorien während der Berufsbiografie und der zeitgewichtete Mittelwert wurden analysiert. Die niedrigste Kategorie im Vergleich zur Höchsten ergab für den zeitgewichteten Mittelwert ein signifikant erhöhtes Risiko. Eine Abwärtsmobilität von H→L, sowie Schichtstabilität (M→M und L→L) ergaben erhöhte Risiken im Vergleich zu H→H. Die Assoziation zwischen sozialem Prestige und UADT kann nicht vollständig mit confundierenden Variablen erklärt werden. Abwärtsmobilität könnte ein unabhängiger Risikofaktor sein. Verbesserte Verfahren der Einstufung von Expositionen sind bei der Auswertung von epidemiologischen Studien eine ständige Herausforderung. Die Bereitschaft, neue Ansätze zu übernehmen, muss gerade im Bereich sozialer Status vorhanden sein.
doctoral thesis
326 154
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Identifikation von Risikogruppen für myokardinfarktbedingte Letalität und nicht-leitliniengerechte Versorgung unter Patienten mit Nicht-ST-Streckenhebungs-Myokardinfarkt (NSTEMI) oder ST-Streckenhebungs-Myokardinfarkt (STEMI) in Bremen
(2010-09-09)
Günther, Kathrin
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Ahrens, Wolfgang
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Fahle, Manfred
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Ahrens, Wolfgang
Acute myocardial infarction (AMI) is one of the leading causes of death in Germany and other Western industrialized countries. In this study data of the Herz ART Bremen (Heart: AMI and regional TQM in Bremen) Study will be presented. The objective of this study was to identify risk groups among patients with NSTEMI or STEMI for mortality or suboptimal care. In addition, we wanted to identify approaches to optimise medical care of AMI patients. The quality of healthcare for patients with AMI in the city of Bremen was measured for all institutions who were involved in medical care (ambulance, hospitals, cardiac catheter laboratory) by means of standardized record sheets in a 6-month sample period in 2005. We used the Bremen Mortality Index (BreMI) to determine the 1-year mortality. In order to evaluate the treatment of AMI patients we followed the guidelines of the German Cardiac Society.
doctoral thesis
341 130
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Investigating participation in population-based cohort studies using paradata
(2020-05-20)
Langeheine, Malte
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Didelez, Vanessa
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Ahrens, Wolfgang
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Ahrens, Wolfgang
This thesis consists of seven main chapters. In the introduction (Chapter 1) the topics under study are conceptualized within a general framework, the Total Study Error, that classifies errors, linking the error sources to the steps of study design, conduct (data collection) and the estimation of prevalences, incidences or associations. This thesis focuses on non-participation (also called nonresponse or at follow-ups attrition) in population-based cohort studies at baseline or follow-up and investigates mainly topics related to the Total Study Error component nonresponse error (Chapters 2 to 5) and to a minor extent to the component related to measurement error (Chapter 6) mainly including paradata (i.e., information about the process of data collection) (Chapters 3, 5, and 6) in the analysis. While Chapters 2, 3, 5, and 6 are published peer-reviewed scientific papers, Chapter 4 is currently under review. Non-participation is not only a phenomenon of the past, but is a source of error that future cohort studies will have to deal with. Hence, it is imperative to address nonresponse. Attrition may lead to bias in epidemiological cohorts, since participants who are healthier and have a higher social position are less likely to drop out. In Chapter 2, we investigated possible selection effects regarding key exposures and outcomes in the IDEFICS/I.Family study, a large European cohort on the etiology of overweight, obesity and related disorders during childhood and adulthood. In particular, we investigated associations of attrition with sociodemographic variables, weight status, and study compliance and assessed attrition across time regarding children’s weight status and variations of attrition across participating countries. We investigated selection effects with regard to social position, adherence to key messages concerning a healthy lifestyle, and children’s weight status. Attrition was associated with a higher weight status of children, lower children’s study compliance, older age, lower parental education, and parent’s migration background, consistent across time and participating countries. Although overweight (odds ratio 1.17, 99% confidence interval 1.05-1.29) or obese children (odds ratio 1.18, 99% confidence interval 1.03-1.36) were more prone to drop-out, attrition only seemed to slightly distort the distribution of children’s BMI at the upper tail. Restricting the sample to subgroups with different attrition characteristics only marginally affected exposure-outcome associations. Declining response proportions in population-based studies are often countered by extended recruitment efforts at baseline that may, however, result in higher attrition in a subsequent follow-up. In Chapter 3, we analyzed the effect of extended recruitment efforts on attrition at the first follow-up of the child cohort IDEFICS. We used paradata from the German IDEFICS cohort to quantify recruitment effort and classify respondents as completing the recruitment early vs. late for baseline and follow-up separately. Individuals who were late respondents at baseline and early respondents at the follow-up had a higher chance of attrition (odds ratio 1.65, 95% confidence interval 1.19, 2.28) as compared to other groups. An investigation of reasons for non-participation revealed that members of this group were more likely to be not reachable by phone. Although missing data are a major concern in epidemiology, missing data may not necessarily result in biased estimates. Analyzing only the individuals with complete data on the outcome, the exposure, and all explanatory variables, is a very simple and therefore popular strategy of handling missing data known as complete-case analysis. In a regression analysis, complete-case analysis is consistent in general when missingness is unrelated to the outcome given the explanatory variables included in the regression model. However, it appears not widely appreciated that this validity of complete-case analysis critically hinges on correct specifications of the analysis model and a misspecified model might re-introduce bias. In Chapter 4, we illustrated with a simulation how different modeling choices can affect our conclusions even when a complete-case analysis is in principle valid. We based our study on empirical data from the IDEFICS study and simulate only the missingness mechanism assuming different association strengths and different frequencies of missingness. In each scenario, we investigated the performance of three different analysis models using complete-case analysis as well as multiple imputation and inverse probability weighting as methods to correct for missing data. Our results suggest that model misspecification can lead to considerable bias when data contain missing values, even in a scenario where an ideal complete-case analysis is known to be consistent. This bias equally affects multiple imputation, and to a lesser extent, at the cost of precision, inverse probability weighting which requires a correct weighting model. In our example, basic model diagnostics were sufficient to alert us to the misspecification of the simple analysis model with regard to the functional form of the exposure; this was detectable even for the most extreme missingness mechanisms. Another aspect of this thesis was whether we could enhance the response to study invitations (Chapter 5). We therefore conducted a trial embedded within the German National Cohort comparing the responses to study invitations sent in recycled envelopes of grey color vs. envelopes of white color. We analyzed paradata for reactions to the invitation letters by potential subjects, the duration between mailing date of the invitation and active responses, and study participation. Grey envelopes only slightly increased the chance of active responses (odds ratio 1.16, 95% confidence interval: 0.83, 1.62) to the invitation letter. Potential study subjects with German nationality (odds ratio 3.75, 95% confidence interval: 2.07, 7.66) and age groups above 50 years (50-59: odds ratio 1.78, 95% confidence interval: 1.19, 2.69; 60-69: odds ratio 2.25, 95% confidence interval: 1.48, 3.43) were more likely to actively respond to the invitation letter. The duration between mailing date of the invitation and active response was not associated with envelope color, sex, nationality, or age. In Chapter 6, we touched upon a kind of participation mostly regarded as undesired. We analyzed factors associated with the presence of an intimate partner during face-to-face interviews using data from the first wave of the German Family Panel (pairfam). Although the intimate partner is most likely to be the third person present during the interview, an examination of the association of the relationship quality and the presence of the intimate partner is lacking in the literature. Our descriptive analysis revealed that an intimate partner was present in every seventh interview. The opportunity structure, such as the couple’s living arrangements or their employment status, had the greatest influence on the presence of both female and male partners while aspects of the relationship quality were to a minor extent associated with the partner’s presence. Chapter 7 summarizes the main findings of this thesis in light of previous literature and discusses methodological considerations related to the scientific articles presented in this thesis. In conclusion, paradata are valuable information for the investigation of nonresponse and attrition in cases where they capture all the information required to answer a given research question. Paradata are often considered only as a 'by-product', but provide considerable scientific benefit and should be already defined in the planning phase of a study.
doctoral thesis
328 517
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Medical risk factors and late effects of childhood cancer - Etiological and methodological considerations
(2023-07-21)
Brackmann, Lara Kim
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Zeeb, Hajo
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Ahrens, Wolfgang
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Ahrens, Wolfgang
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Marron, Manuela
Many risk factors for childhood and second primary neoplasms originate from the medical field. However, most previously conducted studies showed small sample sizes and inadequate exposure assessments. The present dissertation therefore aims to improve the knowledge on medical risk factors for childhood and second primary cancers. A meta-analysis on the influence of vaccinations on childhood cancer development revealed four inverse associations between vaccinations and leukemia risk. The transcriptomic radiation-response was examined using experimental data from former childhood cancer patients and cancer-free controls from the KiKme study. In irradiation experiments, 4 hours were revealed as the time point with most differentially expressed genes in participants’ skin biopsies. The analysis of these genes showed alteration of metabolic pathways that may implicate cellular senescence. To identify effects of radiation beyond the molecular level, medical exposure during cancer therapy was evaluated by collecting information via validated questionnaires. Exposure to chemotherapeutics was associated with thyroid diseases and lipid metabolism disorders. Finally, the KiKme participants were used to examine late effects of cancer and lifestyle differences. Survivors were more affected by diseases and took more medication than controls. Survivors had a healthier lifestyle compared to controls; however, they exercised less. This dissertation contributes to the knowledge of childhood and second primary cancer development by showing that the risk for cancer development as well as for the occurrence of late adverse effects, can be influenced by medical factors. Overall, these results provide a basis for further elaboration on childhood cancers and its late effects and thus may contribute to a long-term reduction in the burden of the disease by providing options for individualized planning of therapies and identification of individuals in need of more extensive follow-up care.
doctoral thesis
282 217
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Growing up in a digital environment: The role of digital media use in European children’s and adolescents’ health and health behaviours
(2023-07-17)
Sina, Elida
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Haines, Jess
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Ahrens, Wolfgang
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Ahrens, Wolfgang
Background Children’s and adolescents’ health state suffers from the double burden of metabolic and mental health disorders, representing a critical public health matter. As never before, today’s children are growing up in a saturated digital media (DM) environment. Despite the immense opportunities for learning and self-development, little is known about the role of DM exposure on children’s health. Aim This doctoral dissertation aims to provide evidence on the potential association of DM exposure with health outcomes, including metabolic syndrome and cognitive functioning, as well as health behaviours, namely dietary intake, eating habits, and sensory taste preferences in children and adolescents. Methods The present cumulative thesis is constituted of four papers: one systematic literature review (SLR, paper 1) and three original investigations (papers 2, 3, and 4). In paper 1, a total of 35 studies conducted worldwide were reviewed, critically appraised, and synthesized. These studies examined the association of social media (SM) exposure with the dietary intake, breakfast skipping, and nutrition literacy of healthy children and adolescents. The SLR was based on the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) guidelines. The empirical research conducted in papers 2 to 4 used data provided by children aged 2-18 years of IDEFICS/I.Family cohort. The cohort was carried out in three waves across nine European countries. The first examination wave (i.e., baseline, W1) was conducted during 2007-2008, and 16,229 children participated. The second examination wave (i.e., first follow-up, W2) was conducted during 2009-2010 and included 13,596 children. The third examination wave (i.e., second follow-up, W3) was conducted during 2013-2014 and included 9,617 children and adolescents. The overarching aim of the cohort was to identify dietary- and lifestyle-induced health effects in children and adolescents, considering sensitive developmental periods, and to develop a community-based intervention on childhood obesity. Across paper 2 to paper 4, the analysis group varied from 3,261 to 10,359 participants after respective inclusion/exclusion criteria were met. DM exposure (hours/day) was self-reported, including: i) television viewing (TV), ii) computer/game console (PC), iii) smartphone, and iv) internet exposure. The related behaviour of media multitasking, defined as the simultaneous use of several media, was also reported. In paper 2, sensory taste preferences for sweet, fatty, salty, and bitter taste were evaluated via a Food and Beverage Preference Questionnaire. In paper 3, measures of cognitive functioning, namely cognitive inflexibility and decision-making ability were assessed via computerized tests, while emotion-driven impulsiveness was self-reported. In paper 4, metabolic syndrome (MetS) and its components: abdominal obesity (via waist circumference), blood pressure (systolic and diastolic), insulin resistance (homeostasis model assessment for insulin resistance (HOMA-IR) or fasting glucose), and dyslipidaemia (HDL-cholesterol and triglycerides), were objectively measured. Age and sex-specific z-scores and monitoring levels (≥90th percentile, as defined by Ahrens et al. 2014) were considered for each metabolic outcome. The statistical approach used to investigate the associations of interest varied depending on the research questions. Logistic regression models were used to examine associations between exposures and dichotomized outcomes (papers 2 and 3). Latent class analyses were performed to identify underlying patterns of DM exposure (paper 3), based on a combination of using the individual media (in categories). In paper 4, to examine the longitudinal association of DM exposure with MetS and its components, a two-step trajectory approach was used: first, the age-dependent trajectories of DM exposure were calculated using linear mixed models; second, to estimate the association between childhood DM trajectory and MetS at follow-up, generalized linear mixed models were used. Across papers, analyses were stratified by sex, age, country of residence, parental educational status, and family structure, to characterize children and adolescents that are most vulnerable to the potential negative impact of DM exposure. Results The SLR revealed a dose-dependent relationship between SM exposure and daily intake of sugar and caffeine and the consumption frequency of sugar-sweetened beverages in both children and adolescents. SM exposure was also associated with low frequency intake of fruits and vegetables and less frequent breakfast consumption. No association between SM exposure and nutrition literacy was observed. SM exposure, measured either as WhatsApp use, watching YouTube videos, or exposure to SM influencer’s advertising on Instagram, led to an increased intake of unhealthy food and beverages at ad-libitum and after two years. A neuro-physiological mechanism was identified: exposure to digital food images increased the neural activation of brain areas related to reward and attention. Peers’ presence on SM but not of SM influencers, showed a potential to improve adolescents’ vegetable intake. In IDEFICS/I.Family children exposure to DM increased over age, from 2.4 h/day at the age of two years to 5.5 h/day at the age of 16 years. This increase was steeper among boys compared to girls. Country differences were also observed, where Estonian, Cypriot, and Swedish children had the highest DM increase, while Spanish children showed the lowest DM increase. The observational research conducted in paper 2 showed that prolonged DM exposure (>2 h/day) was associated with a high preference score for sweet, fatty, and salty-tasting foods among adolescents, especially females. An inverse association between prolonged DM exposure and bitter taste preference was observed among males. In paper 3, it was observed that one additional hour of exposure to smartphones and the internet, and higher media multitasking was positively associated with children’s emotion-driven impulsiveness and cognitive inflexibility and negatively associated with decision-making ability. Compared to participants with low exposure to all media, participants with “high smartphone and internet, in combination with medium TV and low PC exposure”, showed higher scores for emotion-driven impulsiveness and cognitive inflexibility and a lower score for decision-making ability. In paper 4, it was found that increasing DM exposure during childhood was positively associated with the z-scores of MetS, waist-circumference, HOMA-IR, HDL-c-1, and triglycerides after two or six years. The stratified analyses revealed that associations were independent of moderate to vigorous physical activity. Children with an above-average DM increase over age (DM slope> 0 h/day/year) showed a 22% higher risk for later incident MetS. This risk was higher among boys compared to girls (41% and 10%, respectively). Conclusion The findings of this thesis suggest that DM exposure is associated with unfavorable dietary intake and poor eating behaviors. A neuro-physiological mechanism and a clear impact of peers and SM influencers on the SM environment explain these findings. The results also showed that DM exposure is positively associated with a preference for sweet, fatty, and salty-tasting foods and negatively associated with a preference for bitter-tasting foods. This suggests that DM exposure may lead to obesity by favoring the taste preference of unhealthy foods over healthy ones. Moreover, exposure to modern DM was positively associated with children’s emotion-driven impulsiveness and cognitive inflexibility and inversely associated with decision-making ability. This sheds light on a new potential mechanism by which DM exposure leads to poor mental health in children and adolescents. Finally, the findings support the hypothesis that increasing DM exposure during childhood may be an independent risk factor for metabolic syndrome later in life, with boys being at higher risk. These long-term associations need to be confirmed in other populations of children and adolescents, considering not only duration but also patterns of DM exposure, as well as children with an unfavorable background regarding socio-economic status, learning difficulties, or predisposing mental disorders. Further interdisciplinary, longitudinal studies may consider the interplay between health determinants in the physical and digital environment to identify potential intervening factors to promote children’s health in a hybrid world. Future health interventions may consider a precautionary approach and use the identified mechanisms to increase children’s and adolescents’ resilience against the potential adverse health effects of the digital environment at an early stage of their development.
doctoral thesis
616 572
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Erfassung von körperlicher Aktivität und deren Zusammenhänge mit Übergewicht im Kindes- und Jugendalter
(2021-12-13)
Sprengeler, Ole
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Hebestreit, Antje
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Ahrens, Wolfgang
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Ahrens, Wolfgang
Körperliche Aktivität hat sich mittlerweile als ein Schlüsselfaktor für die Gesundheit im Kindes- und Jugendalter sowie als zentraler Aspekt des Gesundheitsverhaltens etabliert. Trotz des hohen Stellenwertes von körperlicher Aktivität für die Gesundheitsförderung und Prävention – institutionalisiert durch international anerkannte Bewegungsempfehlungen (mindestens 60 Minuten moderate bis intensive körperliche Aktivität pro Tag) – mangelt es nach wie vor an ausreichender Evidenz für präventive Zusammenhänge zwischen körperlicher Aktivität und Übergewicht. Zudem bewegt sich der Großteil aller Kinder und Jugendlichen nicht ausreichend, also entsprechend der Bewegungsempfehlungen. Um im Rahmen der vorliegenden Arbeit einen Beitrag zum o.g. Forschungsgegenstand zu leisten, wurden auf der Datenbasis eines pan-europäischen sowie zweier nationaler Projekten vier Artikel mit unterschiedlichen Schwerpunkten verfasst. Die Ziele der Artikel lagen darin, die longitudinalen Zusammenhänge von körperlicher Aktivität und Gewichtstatus näher zu beleuchten und das Bewegungsverhalten im Tagesverlauf von Schulkindern detailliert zu untersuchen, sodass erfolgversprechende Ansätze für Bewegungsförderung identifiziert werden können. Das übergeordnete Ziel der Arbeit, Ansätze für Bewegungsförderung und Prävention von Übergewicht im Kindes- und Jugendalter zu identifizieren, ergibt sich aus der Synergie der ätiologischen und methodischen Fragestellungen der verschiedenen Studien. Einerseits bestärken die gewonnenen Erkenntnisse die notwendige und flächendeckende Förderung von moderater bis intensiver körperlicher Aktivität und sprechen dafür, dass die regelmäßige Teilnahme am Schul- und Vereinssport geeignete Strategien sind, Schulkinder bei der Erreichung des Ziels ausreichender Bewegung zu unterstützen. Andererseits verdeutlichen die Erkenntnisse, dass Akzelerometer als objektive Erfassungsmethode zwar die beste Wahl sind, um Bewegungsverhalten im Kindes- und Jugendalter zu messen, doch dass auch diese Methode gewisse Limitationen aufweist, die bestenfalls durch ergänzende subjektive Methoden wie Bewegungstagebücher kompensiert werden sollten.
doctoral thesis
488 346
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Associations of sedentary behavior, physical activity, body composition, sleep and vitamin D with bone stiffness
(2021-12-20)
Cheng, Lan
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Aleksandrova, Krasimira
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Ahrens, Wolfgang
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Ahrens, Wolfgang
In children and adolescents, bone modeling and remodeling is highly active in order to expand bone in length and width, to increase bone mass, and to maintain bone shape. Although bone mass acquisition is relatively slow throughout childhood, with the onset of puberty and the growth spurt of height in adolescence the rate of bone mineral accumulation increases, reaching a peak bone mass shortly after a peak height. The peak bone mass is an important predictive factor of osteoporosis in the later life due to the bone loss during ageing. Except for genetic factors, there is an estimated 20 to 40% of the peak bone mass variation contributed to modifiable factors e.g., mechanical loading, physical activity, sedentary behavior, sleep and nutritional factors. However, we are only beginning to identify the specific dimensions and doses of these modifiable factors needed for the short-term and long-term beneficial effects on bone health. The lack of longitudinal epidemiological studies and the conflicting results in the intervention studies among healthy pediatric populations limit our knowledge. Hence, the present thesis aims to provide a better understanding on the associations between physical activity, sedentary behavior, sleep, nutrition and bone health in children and adolescents. The present thesis is based on the data from the IDEFICS/I.Family cohort including children and adolescents aged 2 to 15 years from eight European countries. Three examination waves with repeated measurements were conducted in 2007/2008, 2009/2010 and 2013/2014. In the subgroups, bone stiffness index was measured using calcaneal quantitative ultrasound (QUS) in all examination waves, serum bone formation marker osteocalcin was analyzed using chemiluminescence assays in the first examination wave while serum bone resorption marker C-terminal telopeptides of type I collagen was analyzed in the first and third examination waves. Calcaneal QUS as a validated method to estimate bone health is becoming popular in pediatric populations since it is non-radiating, quick and cost-effective. The measured parameters of broadband ultrasound attenuation and speed of sound, as well as the derived stiffness index are related to bone mass and bone structural properties. Meanwhile, bone resorption and formation markers have been suggested to be sensitive to the changes in environmental factors, hormone levels and treatments. Therefore, stiffness index, osteocalcin and C-terminal telopeptides of type I collagen were considered as bone health outcomes. Body composition in terms of fat mass and fat free mass was derived from objectively measured skinfold thickness. Weight status was estimated from objectively measured body height and weight by calculating body mass index z-scores and cut-offs. Physical activity and sedentary behavior were measured using both self-administrated questionnaires and accelerometers. Sleep duration and quality were evaluated using questionnaires. Consumption frequency of dairy products and usual calcium intake were collected using food frequency questionnaires and 24h-dietary recalls, respectively. Serum 25-hydroxyvitamin D was analyzed using chemiluminescence assays. Linear mixed-effect models were used with adjustments for a cluster effect of country and potential confounders. The major findings were presented and discussed in four published or submitted original papers, final sample sizes that varied in each paper depended on the analysis strategies for different research questions. First, the longitudinal results indicated a positive relationship between fat free mass and stiffness index during growth. Specifically, baseline fat free mass was observed to predict two-year and six-year changes in stiffness index, and six-year changes in fat free mass was also positively associated with change in stiffness index. Meanwhile, the association between six-year changes in fat mass and stiffness index differed by sex and pubertal status, suggesting an inverse association in boys and girls before menarche, but a positive association in girls after menarche (Lan Cheng, et al., Bone. 2019). Second, objectively measured moderate-to-vigorous physical activity (MVPA) was positively associated with the increase of stiffness index over two years and six years of follow-up. These results were supported by the comparable albeit weaker positive associations between self-reported time spent at sports clubs and stiffness index. However, the inverse associations between screen time as a surrogate for sedentary behavior and stiffness index depended on weight status. Specifically, the cross-sectional association between weekly duration of watching TV and stiffness index was observed to be inverse only in thin/normal weight group. Both baseline and two years change in weekly duration of watching TV, and six years change in weekly duration of playing computer/games were inversely associated with corresponding changes in stiffness index in the overweight/obese group (Lan Cheng, et al., Int J Behav Nutr Phys Act. 2020). Third, the association between sleep and stiffness index was analyzed using data from two follow-up examination waves with the interval of approximately four years. Total sleep duration was calculated and further classified into short, adequate and long based on the recommendation from the National Sleep Foundation. Poor sleep quality was estimated by reporting either having trouble to get up in the morning, or having difficulty to fall asleep, or have no regular bedtime routine. The positively cross-sectional associations between nocturnal sleep duration, daytime napping and stiffness index were only observed in participants with adequate sleep duration. After four years of follow-up, the positive association between daytime napping and stiffness index was more pronounced in participants with short sleep duration. Moreover, long-term detrimental effect of extreme sleep duration (short or long) on stiffness index only existed in participants with poor sleep quality (Lan Cheng, et al., Osteo Int. 2020). At last, only cross-sectional analyses were conducted in the associations between vitamin D, bone turnover markers and stiffness index using merged datasets based on the first and third examination waves. Serum 25-hydroxyvitamin D, calcium intake and dairy products consumption were observed to be inversely associated with bone resorption marker but not formation marker. MVPA modified the association between 25-hydroxyvitamin D and stiffness index, suggesting that serum 25-hydroxyvitamin D no less than 20 ng/ml would be a protective factor for calcaneal stiffness index only if children met the MVPA guideline of one hour MVPA per day on average (Lan Cheng, et al., Am J Clin Nutr. submitted). In summary, the present cumulative thesis provides a comprehensive understanding on the associations between lifestyle-related factors and bone health indicators in children and adolescents. Future prevention and intervention studies with regard to improving childhood bone health should put emphasis on promoting sufficient MVPA, maintaining adequate sleep duration and calcium intake, and improving consumption frequency of dairy products. Some bone health determinants in specific groups i.e. excess fat mass in boys and pre-pubertal girls, long screen time in overweight/obese children, and insufficient vitamin D level in inactive children particularly need attention.
doctoral thesis
301 348
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Accelerometers in Young Children: Methodological Considerations and Cross-sectional and Longitudinal Associations with Motor Abilities, Physical Fitness, and Cognitive Function
(2021-08-26)
Breau, Becky
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Donnelly, Allan
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Ahrens, Wolfgang
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Ahrens, Wolfgang
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Vallis, Lori Ann
Physical activity plays an important role during early childhood and has favourable associations with numerous health outcomes. It is thought that lifestyle and physical activity behaviours may develop within the first five years of life, making the early years an optimal time for targeted intervention and observation. Accelerometers are valid and reliable devices that allow researchers to quantify large amounts of free-living data in young child populations. However, use of these devices are accompanied by many methodological decisions which can create inconsistencies and limit comparability within the literature. The focus of this thesis was to extensively review current methods being used to analyse accelerometer data from young children, examine how certain methodologies affect interpretation of accelerometer outputs, and observe subsequent cross-sectional and longitudinal associations between physical activity and health. An extensive review revealed that hundreds of published studies use accelerometers with a wide variety of data collection and analysis methods to track movement in young children. Applying different thresholds or cutpoints to quantify movement behaviours into specific intensities of movement demonstrated that choice of cutpoint significantly impacts amounts of time spent in each intensity as well as the number of children categorized as meeting physical activity guidelines. A cross-sectional analysis showed that preschool-aged children who met physical activity guidelines did not have greater levels of individual motor abilities compared to children not meeting guidelines, however sports club membership may influence motor ability development. In a longitudinal analysis, children who met physical activity guidelines during early childhood were more likely to meet guidelines during later childhood/adolescence. Additionally, performance on certain physical fitness tests at baseline also predicted greater amounts of time in physical activity and meeting physical activity guidelines at follow-up. Interestingly, meeting physical activity guidelines showed no associations with cognitive function, and some physical fitness tests showed statistically significant associations, but models did not show a substantial goodness of fit. In summary, future work should continue to investigate associations between meeting physical activity guidelines and health outcomes in young children. Given the importance of this work, we strongly encourage researchers to adapt and apply our recommended, standardized accelerometry reporting practice.
doctoral thesis
188 130
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The connection between mental and physical health: Investigating the associations between psychosocial well-being, sleep and cardio-metabolic health in European children and adolescents
(2021-01-25)
Thumann, Barbara
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Braet, Caroline
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Ahrens, Wolfgang
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Ahrens, Wolfgang
Die kumulative Dissertation besteht aus vier Originalarbeiten, die das Ziel haben, Aufschluss über die Zusammenhänge zwischen psychosozialem Wohlbefinden und kardiometabolischen Markern zu geben. Ein besonderer Schwerpunkt liegt auf der Rolle von Schlaf als einen potenziellen verbindenden Faktor.
doctoral thesis
351 691

Ahrens, Wolfgang

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