Chronotype and Arterial Stiffness: Moderating Effect of Cardiorespiratory Fitness in Middle-Aged and Older Adults.

BACKGROUND: This cross-sectional study examined whether cardiorespiratory fitness modified the association between chronotypes and arterial stiffness in middle-aged and older adults. METHODS: This study included 1,112 participants (734 men and 378 women) aged ≥40 years from the Waseda Alumni's Sports, Exercise, Daily Activity, Sedentariness and Health Study. Definitely morning/moderately morning/neither/moderately evening were assessed using the Morningness-Eveningness Questionnaire. Arterial stiffness was evaluated by cardio-ankle vascular index. Cardiorespiratory fitness was directly measured as peak oxygen uptake (⩒O2peak) during a maximal exercise stress test and categorized into sex- and age-specific tertiles (relatively low/moderate/high cardiorespiratory fitness). Cardio-ankle vascular index by chronotype of each cardiorespiratory fitness level category was compared, and the results were adjusted for age, sex, body mass index, triglyceride level, Pittsburgh sleep quality index score, smoking status, alcohol intake, and total energy intake. RESULTS: A significant interaction in a two-way analysis of covariance (ANCOVA) between chronotype and cardiorespiratory fitness on cardio-ankle vascular index was observed (P = 0.007). Definitely morning-type individuals showed 0.64 (95% CI: 0.18-1.11) higher in cardio-ankle vascular index than moderately morning-type, 0.64 (95% CI: 0.18-1.10) higher than neither type, and 0.70 (95% CI: 0.05-1.35) higher than moderately evening-type individuals after adjusting for confounders in the relatively low cardiorespiratory fitness group. CONCLUSIONS: In this population, the association between the definitely morning chronotype and high cardio-ankle vascular index may be more apparent when the cardiorespiratory fitness is low.