Night owls are more susceptible to diabetes and heart disease

Those who stay up later have a reduced ability to use fat for energy.


Undoubtedly, patterns of our activities and sleep cycles have a significant impact on our health. A new study by Rutgers University, New Jersey, USA, found wake/sleep cycles cause metabolic differences and alter our body’s preference for energy sources. The study suggests that people who are night owls tend to have a reduced ability to use fat for energy, increasing the risk for type 2 diabetes and cardiovascular disease.

People who are early birds rely more on fat as an energy source. They are more likely to be active during the day with higher aerobic fitness levels. In contrast, people who are night owls use less fat for energy at rest and during exercise.

The study involved 51 participants, which were classified into two groups (early and late) based on their ‘chronotype.’ The chronotype is our natural propensity to seek activity and sleep at different times.

They could assess participants’ body mass and body composition using advanced imaging. They also evaluated insulin sensitivity and breath samples to measure fat and carbohydrate metabolism.

The activity patterns of the participants were evaluated throughout a week of monitoring.

To minimize the impact of diet on the outcomes, they had to fast overnight while following a calorie and nutrition-controlled diet. To study fuel preference, they were tested 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% every two minutes until the participant reached a point of exhaustion.

Researchers discovered that early birds burn more fat for energy during exercise and rest than night owls. Additionally, early birds were more insulin sensitive. Contrarily, night owls are insulin resistant, which means their bodies prefer carbohydrates to fats as an energy source and need more insulin to drop blood glucose levels. 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 and/or heart disease. The cause for this shift in metabolic preference between early birds and night owls is unknown and needs further investigation.

Senior author Professor Steven Malin, Rutgers University, New Jersey, USA, said: “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. This observation advances our understanding of how our body’s circadian rhythms impact our health. Because chronotype 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.”

“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.”

Journal References:

  1. Early Chronotype with Metabolic Syndrome favors Resting and Exercise Fat Oxidation in Relation to Insulin-stimulated Non-Oxidative Glucose Disposal. Experimental Physiology. DOI: abs/10.1113/EP090613
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