"Night owls" may have greater risk of heart disease

A new study led by Rutgers University has found that our activity patterns and sleep cycles could significantly influence our risk of developing health conditions such as type 2 diabetes or heart disease. According to the experts, wake/sleep cycles cause metabolic differences and alter our body’s preference for energy sources. 

Thus, “night owls” (people who stay up late in the evening) have a reduced capacity to use fat for energy, meaning that fats can build-up in their bodies and increase the risk for diabetes and cardiovascular diseases. By contrast, “early birds” (people who prefer to be active in the morning), rely more on fat as an energy source and are more active during the day, with higher levels of aerobic fitness than the “night owls.” These metabolic differences seem to relate to how well each group can use insulin to promote glucose uptake by the cells for storage and energy use.

“The differences in fat metabolism between ‘early birds’ and ‘night owls’ shows that our body’s circadian rhythm (wake/sleep cycle) could affect how our bodies use insulin. A sensitive or impaired ability to respond to the insulin hormone has major implications for our health,” said study senior author Steven Mallin, an expert in Metabolism and Endocrinology at Rutgers. 

“This observation advances our understanding of how our body’s circadian rhythms impact our health. Because chronotype appears to impact our metabolism and hormone action, we suggest that chronotype could be used as a factor to predict an individual’s disease risk.”

The researchers enrolled 51 participants classified into two groups based on their chronotype (night owls versus early birds), and monitored them for a week to assess their activity patterns during the day. Moreover, they used advanced imaging techniques to assess their body mass and composition, insulin sensitivity, and fat and carbohydrate metabolism. Finally, the scientists tested participants’ fuel preference and aerobic fitness by engaging them in exercise sessions on a treadmill. 

The analyses revealed that early birds are more insulin sensitive and use more fat for energy both while at rest and during exercise. On the other hand, night owls were insulin resistant, and their bodies preferred carbohydrates as an energy source rather than fats. Their impaired ability to respond to insulin to promote fuel use could have a negative impact on their health, indicating a higher risk of developing diabetes or heart disease.

Further research is needed to clarify the cause for this shift in metabolic preference between early birds and night owls and to better understand the relation between chronotype, exercise, and metabolic adaptation.

The study is published in the journal Experimental Physiology. 

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By Andrei Ionescu, Earth.com Staff Writer