Night owls could have greater risk of type-2 diabetes and heart disease

The metabolic differences relate to how well early risers and night owls can use insulin created by the pancreas to promote glucose uptake by the cells for storage and energy use.

Individuals 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 while people who prefer to be active later in the day and the night use less fat for energy at rest and during exercise.

“The differences in fat metabolism between ‘early birds’ and ‘night owls’ show that our body’s circadian rhythms (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 Steven Malin, author of the study and a professor at Rutgers University in the US, in a statement.

He added that this observation “advances our understanding of how our body’s circadian rhythms impact our health”.

The professor also said: “Because chronotype (the natural inclination of your body to sleep at a certain time) 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 study

Researchers from Rutgers University classified 51 participants into two groups (early and late) based on their chronotype.

They used advanced imaging to assess body mass and body composition, as well as insulin sensitivity and breath samples, to measure fat and carbohydrate metabolism.

Participants were monitored for a week to assess their activity patterns across the day. They ate a calorie and nutrition-controlled diet, and had to fast overnight to minimise any dietary impact on the results.

Researchers found that the early birds used more fat for energy at both rest and during exercise than night owls. Early birds were also more insulin-sensitive.

Night owls, on the other hand, were insulin resistant, meaning their bodies required more insulin to lower blood glucose levels, and their bodies favoured carbohydrates as an energy source over fats.

This group’s impaired ability to respond to insulin to promote fuel use could be harmful as it indicated a greater risk of type-2 diabetes and/or heart disease.

The cause for this shift in metabolic preference between early birds and night owls is as yet unknown and needs further investigation.

“We also found that early birds are more physically active and have higher fitness levels than night owls, who are more sedentary throughout the day. Further research is needed to examine the link between chronotype, exercise, and metabolic adaptation to identify whether exercising earlier in the day has greater health benefits,” said Malin.