Individual preferences in bed- and waking up time, as well as in the time of day to devote to activity, define three chronotypes: larks, who prefer to wake up early and are most productive in the first part of the day; night owls, who prefer to stay up late at night and tend to be active in the second part of the day; and intermediates, who represent the majority of us. It is known from previous studies that evening types are more likely to develop cardio-metabolic diseases, such as type II diabetes and hypertension. An international research team shed light on the relationship between chronotype and metabolic syndrome, exploring for the first time the respective contribution of genetics and lifestyle.

More than 2,000 participants were recruited, equally distributed according to chronotype. Results showed a clear prevalence of cardiovascular risk factors (such as higher body weight, higher triglyceride levels, insulin resistance) among evening as compared to morning types. Night owls also showed a greater tendency to engage in unhealthy lifestyles that could explain this result, such as sedentariness, higher caloric intake, eating larger meals with less self-control, and higher alcohol consumption. In contrast, no association emerged between genetics predisposing to eveningness and metabolic syndrome risk factors.

The authors conclude that, as much as a particular genetic make-up may contribute to determine individual chronotype, the higher metabolic risk observed in evening types seems to be mainly related to their lifestyle choices, highlighting the importance of modifiable risk factors in the prevention of chronic diseases.