'Night owls' may have higher risk of diabetes, heart disease: Study

Washington: People who stay up till late in the night may have an increased risk for type 2 diabetes and cardiovascular disease, a study suggests.

The researchers from Rutgers University in the US noted that 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 ‘night owls’.

On the other hand, people who prefer to be active later in the day and night use less fat for energy at rest and during exercise.

"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 Professor Steven Malin, from Rutgers University.

"A sensitive or impaired ability to respond to the insulin hormone has major implications for our health. This observation advances our understanding of how our body's circadian rhythms impact our health," Malin said.

The study, published in the journal Experimental Physiology, classified 51 participants into two groups -- early birds and night owls -- based on their chronotype or natural propensity to seek activity and sleep at different times.

The researchers 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 dietary impact on the results.

They were tested while at rest before completing two 15-minute bouts of exercise: one moderate and one high intensity session on a treadmill.

Aerobic fitness levels were tested through an incline challenge where the incline was raised 2.5 per cent every two minutes until the participant reached a point of exhaustion.

Researchers found that 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, are insulin resistant, meaning their bodies require more insulin to lower blood glucose levels, and their bodies favoured carbohydrates as an energy source over fats, the researchers said.

This group's impaired ability to respond to insulin to promote fuel use can be harmful as it indicates a greater risk of type 2 diabetes or heart disease, according to the researchers.

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

"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," Malin added.