Are you an owl or a lark? The former feel more energy in the afternoon, it is difficult for them to go to bed, but also to get up early. However, the latter are able to get up very early and quickly become active. In addition to the benefits or inconveniences that activity patterns and sleep cycles can bring to your daily life, new research shows that they can affect your risk of diseases such as type 2 diabetes and heart disease.
The study, published in Experimental Physiology, found that sleep/wake cycles cause metabolic differences and change our body’s preferences for energy sources. Thus, those who stay awake later show a reduced ability to use fat for energy, meaning that it can accumulate in the body and increase the risk type 2 diabetes and cardiovascular disease.
Metabolic differences are based on how well you can use insulin each group in order to promote the uptake of glucose by cells for energy storage and use.
Early risers rely more on fat for energy and are more active during the day with higher levels of aerobic fitness than night birds. While the latter use less fat for energy at rest and during exercise.
Researchers from Rutgers University (New Jersey, USA) classified 51 participants into two groups based on their chronotype (our natural tendency 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 throughout the day. They ate a calorie-controlled diet and had to fast overnight to minimize the diet’s impact on the results. To study fuel preferences, they were tested at rest before completing two 15-minute bouts of exercise: one moderate-intensity session and one high-intensity treadmill session. Aerobic fitness levels were assessed by a challenge where the incline was increased by 2.5% every two minutes until the participant reached the point of exhaustion.
The researchers found that people with the lark profile use more fat for energy both at rest and during exercise than night owls. Early risers were also more insulin sensitive. However, night owls are insulin resistant, meaning their bodies need more insulin to lower blood sugar levels, and their bodies prefer carbohydrates for energy over fat. This group’s poor ability to respond to insulin and promote fuel use can be detrimental, indicating an increased risk of type 2 diabetes and/or heart disease. The reason for this difference in metabolic preferences between early risers and night owls is still unknown and needs further investigation.
“Differences in fat metabolism between early risers and night owls show that our body’s circadian rhythm (wake/sleep cycle) can affect how our bodies use insulin.” Impaired ability to respond to the hormone insulin has important consequences for our health. This observation improves our understanding of how our body’s circadian rhythms affect our health. Since chronotype appears to influence our metabolism and hormone action, we hypothesize that chronotype can be used as predictor of risk of the individual’s disease,” says Professor Stephen 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 birds, who are more sedentary during the day.” More research is needed to find out relationship between chronotype, exercise and metabolic adaptation to establish whether exercising earlier in the day has greater health benefits,” concludes Professor Malin.