Chronotype and metabolic syndrome in midlife: findings from the Northern Finland Birth Cohort 1966

Evening chronotype is known to be associated with various chronic diseases and cardiovascular risk factors. Metabolic syndrome is a group of conditions that together raise the risk of coronary heart disease, diabetes, stroke, and other serious health problems. Only a few studies have been published on the association between chronotype and metabolic syndrome in unselected population data, with conflicting results. The aim of this study was to evaluate the association between chronotype and metabolic syndrome at population level by using unselected Northern Finland Birth cohort 1966 (NFBC1966) database. The study population consists of participants with NFBC66 (n = 5,113, 57% female) at the age of 46 yr old. Chronotype was determined with shortened Morningness-Eveningness Questionnaires and expressed as morning (44%), intermediate (44%), and evening types (12%). Metabolic syndrome was determined according to the definition of International Diabetes Federation. One-way ANOVA, Kruskal-Walli's test, and χ² tests were used to compare the chronotype groups, followed by logistic regression analysis (adjusted with alcohol consumption, smoking, marital status, level of education, and leisure-time physical activity). In women, the prevalence of metabolic syndrome was statistically significantly higher in the evening type group: 23, 24, and 34% for morning, intermediate, and evening groups, respectively (P < 0.001). In logistic regression analysis, evening chronotype was associated with higher risk of having metabolic syndrome (OR 1.5; CI 95% 1.2 to 2.0). In this population-based birth cohort study, the evening chronotype was independently associated with higher prevalence of metabolic syndrome in women.NEW & NOTEWORTHY Only a few studies have been conducted on the association between chronotype and metabolic syndrome in unselected population data, with conflicting results. In this population-based cohort study of 5,113 participants, the evening chronotype associated with metabolic syndrome in women when there was no such association in men. The result supports a previous South Korean population study of 1,620 participants, in which the association was also found in women, but not in men.