‘Night owls’ could have higher risk of type 2 diabetes and heart disease than ‘early birds’

Summary: Early birds use more fat for energy during both rest and exercise than night owls. Early risers are also more insulin sensitive, while late risers are more insulin resistant, meaning they need more insulin to lower blood glucose levels and are more prone to consume carbohydrates as a source of energy than fats.

Source: The Physiological Society

Are you an early riser or a night owl? Our activity patterns and sleep cycles could influence our risk of diseases such as type 2 diabetes and heart disease.

New research published in Experimental physiology Sleep/wake cycles cause metabolic differences and alter our body’s preference for energy sources.

Researchers found that those who stay up later have a reduced ability to use fat for energy, meaning that fat can build up in the body and increase the risk of type 2 diabetes and cardiovascular disease.

The metabolic differences relate to how each group can use insulin to promote the uptake of glucose by cells for energy storage and use.

People who are “mature” (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 than “nighters”.

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

Researchers from Rutgers University, New Jersey, USA, classified the participants (n=51) into two groups (early and late) based on their “chronotype”: our natural propensity to seek activity and sleep at different times.

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 throughout the day. They ate a calorie- and nutrition-controlled diet and had to fast overnight to minimize the impact of diet on the results.

To study fuel preference, they were tested at rest before completing two 15-minute exercise sessions: one moderate-intensity and one high-intensity session on a treadmill.

Aerobic fitness levels were tested using an incline challenge where the incline was increased by 2.5% every two minutes until the participant reached a point of exhaustion.

The researchers found that early birds use more fat for energy both at rest and during exercise than night owls. The early birds were also more sensitive to insulin. Night owls, on the other hand, are insulin resistant, meaning their bodies need more insulin to lower blood glucose levels, and their bodies favored carbohydrates as an energy source over fats

The researchers found that early birds use more fat for energy both at rest and during exercise than night owls. The image is in the public domain

This group’s impaired ability to respond to insulin to promote fuel use can be harmful, indicating an increased risk of type 2 diabetes and/or heart disease. The cause of this shift in metabolic preference between early birds and night owls is still unknown and requires further investigation.

Lead author Professor Steven Malin of Rutgers University, New Jersey, USA, said:

“Differences in fat metabolism between ‘early birds’ and ‘night birds’ show that our body’s circadian rhythm (wake/sleep cycle) could affect how our body uses insulin. A sensitive ability or altered response to the hormone insulin has important implications for our health.

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

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“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 during the day has greater health benefits.”

About this circadian rhythm and health research news

Author: Alanna Orpen
Source: The Physiological Society
Contact: Alanna Orpen – The Physiological Society
Image: The image is in the public domain

Original Research: Open access
“Early chronotype with metabolic syndrome favors fat oxidation at rest and exercise relative to insulin-stimulated nonoxidative glucose disposal” by Steven Malin et al. Experimental physiology


Summary

Early chronotype with metabolic syndrome favors fat oxidation at rest and exercise relative to insulin-stimulated nonoxidative glucose disposal

New findings

  • What is the central question of this study? Chronotype reflects differences in circadian-mediated hormonal and metabolic profiles. But does resting and/or exercise fuel use differ in the early and late chronotype with respect to insulin sensitivity?
  • What is the main finding and its significance? Early chronotypes with metabolic syndrome used more fat during rest and exercise regardless of aerobic fitness compared to late chronotypes. Early chronotypes were also more physically active throughout the day. Greater fat use was linked to non-oxidative glucose disposal. These findings suggest that early chronotypes have differences in fuel selection that are associated with type 2 diabetes risk.

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