Javascript is not enabled.

Javascript must be enabled to use this site. Please enable Javascript in your browser and try again.

Skip to content
Content starts here


Leaving Website

You are now leaving and going to a website that is not operated by AARP. A different privacy policy and terms of service will apply.

Night Owls May Risk Diabetes, Heart Disease

Research suggests sleep cycle may affect metabolism in potentially harmful ways

spinner image portrait of an eagle owl very close up with black background
Alan Tunnicliffe Photography

Adults who sleep late may be at greater risk of developing type 2 diabetes and heart disease than those who are early risers, according to a recently published study.

Appearing in the journal Experimental Physiology, the research found differences in the metabolisms of so-called night owls and early birds that make it more difficult for night owls to burn fat. As a result, the researchers suggest, night owls are at greater risk of developing type 2 diabetes and heart disease.

spinner image Image Alt Attribute

AARP Membership— $12 for your first year when you sign up for Automatic Renewal

Get instant access to members-only products and hundreds of discounts, a free second membership, and a subscription to AARP the Magazine.

Join Now

“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,” study author Steven Malin, an associate professor of metabolism and endocrinology at Rutgers University, said in a statement.

What the study did

Study participants included 51 nonsmoking healthy adults (mostly white women around 54 to 55 years old) who participated in less than an hour of structured exercise per week. They were divided into two groups — early birds and night owls — depending on their sleep habits. Each was examined by a physician at the outset. Advanced imaging was used to assess body mass and body composition, as well as insulin sensitivity. Breath samples were also taken to measure fat and carbohydrate metabolism.

Study participants were monitored for a week, during which they were given calorie- and nutrition-controlled meals to minimize dietary impact on the results. Study participants had their aerobic fitness levels tested, and researchers assessed their activity patterns across the day. They found early birds to be more physically active and to have higher fitness levels than night owls, who were more sedentary throughout the day.

Study participants also were tested three times — at rest, after moderate exercise and after intense exercise — to determine their fuel preference — fat or carbohydrates. Night owls favored carbohydrates as an energy source over fats and required more insulin to lower blood glucose levels than early birds, who used more fat for energy both at rest and during exercise. They were also more insulin sensitive.

What it means

Insulin resistance and the buildup of fat in the body put night owls at greater risk of developing either type 2 diabetes or heart disease. The cause of this shift in metabolic preference, however, is not known and requires further investigation, according to the researchers. 

Discover AARP Members Only Access

Join AARP to Continue

Already a Member?