Chronotype and mortality - a 37-year follow-up study in Finnish adults

Abstract

AbstractBackgroundThe only study on chronotype and mortality suggested small increases of all-cause and cardiovascular mortality in a 6.5-year follow-up. Our aim was to constructively replicate findings from it in a longer follow-up.MethodsA questionnaire was administered to the population-based Finnish Twin Cohort in 1981 (response rate 84%, age 24–101 years). The study population included 23,854 participants who replied to the question: “Try to assess to what extent you are a morning person or an evening person”, with four response alternatives (clearly a morning person, to some extent a morning person, to some extent an evening person, and clearly an evening person). Vital status and cause of death data were provided by nationwide registers up to the end of 2018. Hazard ratios and their 95% confidence intervals for mortality were computed; there were 8728 deaths over the follow-up period. Adjustments were made for education, alcohol, smoking, body mass index, and sleep length.ResultsThe model adjusted for all covariates showed a 9% increase in risk of all-cause mortality for the evening-type group (1.09, 1.01–1.18), with attenuation mainly due to smoking and alcohol, as they had larger consumption than those with morningness chronotypes. We observed no increase in cardiovascular mortality by chronotype. No increase in mortality was seen among the non-smokers who were at most light drinkers.ConclusionsOur results from this 37-year follow-up study suggest that there is little or no independent contribution of chronotype to all-cause and cardiovascular mortality.Key messagesThere is little or no independent contribution of chronotype to mortality.The increased risk of mortality associated with eveningness appears to be mainly mediated by a larger consumption of tobacco and alcohol than in those with a morningness chronotype.It is important to be aware of the increased health risks of evening-type persons.