Sleep duration and its role in the aetiology of cardio-metabolic health outcomes

Abstract

An adequate amount of sleep is believed to be important for optimal health and functioning throughout life and changes in sleep duration were found to be associated with several especially cardio-metabolic - health outcomes in adults as well as in children. The factors that influence sleep duration are multi-factorial and the interplay between sleep duration and other factors in the aetiology of cardio-metabolic outcomes is complex and not fully understood yet. Internationally comparable data from children aged 2 to 9 years participating in the IDEFICS study has been analysed to investigate on differences in and determinants of sleep duration as well as on the association between sleep duration and overweight in children. Systematic reviews give an insight in the literature on the longitudinal relationship between sleep duration and weight status in children and adults on the one hand, and on the epidemiological evidence regarding sleep duration and cardiovascular mortality on the other hand. A meta-analysis has been conducted to quantify the dose dependency of the association between sleep duration and cardiovascular mortality. Nocturnal sleep duration differed significantly (P < 0.001) by up to 1.7 hours between countries in univariate as well as in multivariate analysis. Disparities between Northern, Southern and Eastern Europe were striking, with children from Northern countries sleeping the longest. The factor that was found to mainly affect children s sleep duration was country affiliation. Age also had a significant effect in all models, but accounted for less change in sleep duration than country. No association was found with behavioral aspects or environmental factors, such as season or daylight. A negative association of sleep duration with a higher probability of being overweight was revealed. This relationship was attenuated by an adjustment for geographic region, whereas no effect modification by region was found. Generally the association appeared to be much stronger in school children than in preschool children. The relationship between sleep duration and weight status can not only be seen in children but also in adults even if the results are less consistent with increasing age. The meta-analysis showed a clear dose-effect relationship of sleep duration on cardiovascular mortality. For stroke and cardiovascular diseases in general (CVD) the association could mainly be seen with sleep durations of more than 7.5 hours and the direction of the relationship seemed to be similar in men and in women. For coronary heart disease (CHD)the effects of sleep duration were generally stronger, but differed between sexes, with short sleep duration being associated with CHD to a higher extent in men than in women. In contrast, long sleep duration seemed to increase the risk in women, while no significant effect was seen in men. In conclusion we suggested a twofold effect of sleep duration on cardiovascular outcomes: directly and indirectly via the effect of overweight. Furthermore, investigation on sleep duration as a tracking risk factor for cardio-metabolic outcomes as well as internationally comparable studies to give insight in regional aspects of sleep duration was proposed. Such research might create the basis for specific and appropriate public health actions with regard to sleep induced cardio-metabolic conditions.