Metabolic study finds night owls more susceptible to diabetes, heart disease


Researchers from Rutgers University have conducted a close investigation of the metabolic differences between night owls and early birds, finding those who prefer staying up late may be at greater risk of type 2 diabetes and heart disease.

Are you a night person? Maybe you function better in the evenings, and naturally stay up late. Informally you are known as a night owl, someone who gravitates to circadian rhythms slightly out of sync with most people.

Studies have found night owls often display higher rates of diabetes and neurological disorders. A large study tracking half a million people for nearly seven years found night owls had a 10% higher risk of death compared to morning people.

Aside from social and behavioral factors, such as irregular eating or exercise, that can lead to ill health in night owls, researchers have not known whether those with late-night tendencies harbor fundamental metabolic differences to those early morning larks. This new study set out to home in on that particular question by closely investigating 51 volunteers, evenly split between night owls and early birds.

All participants were aged in their mid 50s and lived a relatively sedentary lifestyle. They were all free of any diseases such as diabetes or cancer, however, they were classified as having mild metabolic syndrome. This means they presented with symptoms such as high blood pressure, elevated fasting glucose or increased waist circumference.

The cohort was closely monitored for a week to track physical activity patterns before being called into the lab for a day of metabolic tests. The experiments were designed to measure how the body processes fat and carbohydrates into energy.

The results revealed the morning people were more insulin sensitive and better at using fat for energy compared to the night owls. In contrast, the night people relied more on processing carbohydrates for energy and displayed signs of insulin resistance.

“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,” said Steven Malin, senior author on the study. “A sensitive or impaired ability to respond to the insulin hormone has major implications for our health.”

The researchers conclude these metabolic differences may make night owls more susceptible to cardiovascular disease and type 2 diabetes. However, as with all research, there are some caveats.

The study unfortunately cannot clearly answer whether night owls are intrinsically geared for these metabolic differences. The activity tracking in the week prior to the lab experiments revealed the early birds were more physically active overall compared to the night owls.

So the big lingering question is whether the metabolic differences between the two groups are simply a reflection of differences in physical activity. Or, is physical activity more metabolically beneficial when performed in the morning compared to the night?

“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,” Malin noted.

At the very least, the researchers do indicate the findings affirm night owls likely face higher risk for cardiovascular and metabolic disease. And despite the reasons still being unclear, those with a propensity for staying up late should be aware of this increased risk.

The new study was published in the journal Experimental Physiology.

New Atlas, 20 September 2022