Modifiable lifestyle behaviors, but not a genetic risk score, associate with metabolic syndrome in evening chronotypes

Evening chronotype associates with health complications possibly via lifestyle factors, while the contribution of genetics is unknown. The aim was to study the relative contributions of genetics, lifestyle, and circadian-related physiological characteristics in metabolic risk of evening chronotype. In order to capture a biological contribution to chronotype, a genetic-risk-score (GRS), comprised of 15 chronotype-related variants, was tested. Moreover, a wide range of behavioral and emotional eating factors was studied within the same population. Chronotype, lifestyle, and metabolic syndrome (MetS) outcomes were assessed (n = 2,126), in addition to genetics (n = 1,693) and rest-activity/wrist-temperature rhythms (n = 100). Evening chronotype associated with MetS and insulin resistance (P < 0.05), and several lifestyle factors including poorer eating behaviors, lower physical activity and later sleep and wake times. We observed an association between higher evening GRS and evening chronotype (P < 0.05), but not with MetS. We propose a GRS as a tool to capture the biological component of the inter-individual differences in chronotype. Our data show that several modifiable factors such as sedentary lifestyle, difficulties in controlling the amount of food eaten, alcohol intake and later wake and bed times that characterized evening-types, may underlie chronotype-MetS relationship. Our findings provide insights into the development of strategies, particularly for evening chronotype.