Increasing evidence suggests that being an individual type of risk of developing  type 2 diabetes  and cardiovascular disease, likely through a combination of poor diet, erratic eating patterns, and irregular sleeping hours, say European researchers.

They are calling for more research on the different aspects of this phenomenon so that any lessons can help in modifying the behavior of those at risk. An individual's morning or evening preference is dictated by their chronotype, or internal circadian clock system.

Researchers reviewed the literature to determine the relationship between chronotype, lifestyle, and cardiometabolic disease risk. They found that an individual's morning or evening preference is affected by a range of genetic, ethnic, and societal factors. This, in turn, is associated with differences in dietary intake, timing of eating (or chrononutrition), and sleeping patterns, with night owls more likely to have an unhealthy, unstable lifestyle.

Consequently, the risk of type 2 diabetes is increased in twilight in evening types versus early birds, an effect seen in most starkly in rotating shift workers. The review,  published online  in  Advances in Nutrition , also highlights that diabetes control is more common in evening types.

"Scientific evidence is providing increasing insight into the relationship between your chronotype, diet, and cardiometabolic health," noted senior author Leonidas G. Karagounis.  "Overall, cross-sectional studies suggest that an evening chronotype is associated with lower intake of fruits and vegetables, and higher intake of energy drinks, alcoholic, sugary, and caffeinated beverages, as well as higher energy intake from fat."

Lifestyles Misaligned With Circadian Rhythms in Modern Society

The authors point out that, in modern societies, it is common for individuals to have lifestyles that are "misaligned" with their circadian clock system and the daily light-dark cycle, and to eat at "physiologically inappropriate times of the day." To examine the impact of these processes and risks, the authors conducted a nonsystematic literature review, without specifying how the studies were chosen.

Chronotype can be assessed by a range of measures, the authors explain, including dim-light  melatonin  onset and several self-report questionnaires, although the latter remains valid for validated in large studies. However, the evidence suggests that there are several genetic and environmental factors that influence the distribution of chronotype within a given population.

Several specific mutations in circadian clock regulator genes have been identified, and it has been shown that they have been affected by ethnicity and societal norms, with Germans found to be more likely to have an "evening preference" than, for example, Indians and Slovakians.

More Research Needed on Chrononutrition

Crucially, the authors point out that several studies have demonstrated that an evening chronotype is associated with an increased risk of both cardiovascular disease and type 2 diabetes. One study indicated that an evening preference was associated with a 2.5-fold increased risk of type 2 diabetes compared with a morning preference, as well as a poorer glycemic control among those who already have the disease.

One study showed, for example, that skipping breakfast was associated with higher HbA 1c  levels, even after adjusting for age, sex, race, body mass index, diabetes number,  insulin  use, depressive symptoms, perceived sleep, and percentage of daily caloric intake at dinner.

In contrast, morning people eat slightly more fruits and vegetables per day, including grains and rye, than evening people, and have smaller, more frequent meals and more stable sleeping patterns. Eating later in the day could also affect glucose metabolism.

Glucose levels should decline naturally during the day and reach their lowest point at night before going to sleep. People who eat late in the evening, however, have increased glucose levels just as they are going to bed, again increasing the risk of increasing type 2 diabetes.

Generating more research in this field will potentially help "guide the development of health-promotion strategies aimed at preventing and treating chronic diseases based on an individual's chronotype," they conclude.