Night owls or early risers? These are the ones with the highest risk of diabetes and heart disease

Are you an owl or a lark? The former feel more energy towards the afternoon, it is difficult for them to go to bed, but also to get up early. The latter, however, are capable of getting up very early and quickly becoming active. Beyond the upsides or downsides that activity patterns and sleep cycles can bring to your day-to-day life, new research now suggests they may influence our risk of diseases like type 2 diabetes and heart disease.

The study, published in Experimental Physiology, found that sleep/wake cycles cause metabolic differences and alter our body’s preference for energy sources. Thus, those who stay up later show a reduced ability to use fat for energy, which means that it can accumulate in the body and increase the risk type 2 diabetes and cardiovascular disease.

The metabolic differences are based on how well you can use the insulin each group with the goal of promoting glucose uptake by cells for energy storage and use.

People who are early risers rely more on fat for energy and are more active during the day with higher levels of aerobic fitness than night owls. While the latter use less fat for energy at rest and during exercise.

Researchers at Rutgers University (New Jersey, USA) classified the 51 participants into two groups 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.

The participants were monitored for a week to assess their activity patterns throughout the day. They ate a calorie-controlled diet and had to fast overnight to minimize the impact of the diet on the results. To study fuel preference, they were tested at rest before completing two 15-minute bouts of exercise: one moderate-intensity session and one high-intensity session on a treadmill. Aerobic fitness levels were assessed through a challenge in which the incline was raised 2.5% every two minutes until the participant reached the point of exhaustion.

The researchers found that people with a lark profile use more fat for energy both at rest and during exercise than night owls. Early risers were also more sensitive to insulin. Night owls, however, are insulin resistant, meaning their bodies require more insulin to lower blood glucose levels, and their bodies prefer carbohydrates for energy to fats. The poor ability of this group to respond to insulin and promote fuel use can be detrimental, indicating an increased risk of type 2 diabetes and/or heart disease. The cause of this difference in metabolic preference between early risers and night owls is still unknown and needs further investigation.

“The differences in fat metabolism between early risers and night owls show that our body’s circadian rhythm (wake/sleep cycle) could influence how our bodies use insulin. An impaired ability to respond 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 influence our metabolism and the action of hormones, we suggest that chronotype could be used as a predictor of risk of an individual’s disease,” says Professor Steven Malin of Rutgers University, New Jersey, USA, and lead author of the study.

“We also found that early risers are more physically active and have higher fitness levels than night owls, who are more sedentary during the day. More 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,” Professor Malin concludes.


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