Findings from a Rutgers University study suggest that people who are night owls are at an increased risk of type 2 diabetes and cardiovascular disease.
The research identified that our activity patterns and sleep cycles could significantly influence our risk of type 2 diabetes and heart disease, finding that wake/sleep cycles cause metabolic differences and change our body’s preference for energy sources.
The researchers discovered that people who stay up late – otherwise known as night owls – had a reduced ability to use fat for energy, meaning fat may accumulate and increase the risk of type 2 diabetes and cardiovascular disease.
The research is published in Experimental Physiology.
What are metabolic differences?
Metabolic differences reveal how well certain people can utilise insulin to glucose uptake by the cells for storage and energy use. People who are active in the morning – early birds – rely on fat more as an energy source and have higher anaerobic fitness than night owls. Contrastingly, night owls use less fat for energy at rest and during exercise.
Increasing risk of type 2 diabetes and heart disease
For their study, the researchers divided participants into two groups – night owls and morning owls – based on their chronotype, which is our natural ability to seek activity and sleep at different times. They then employed advanced imaging to examine body mass and composition, insulin sensitivity, and breath samples to assess fat and carbohydrate metabolism.
The participants were monitored for a week to analyse their activity patterns during the day. They consumed a calorie and nutrition-controlled diet and fasted overnight to mitigate the dietary impact on the results.
To test fuel preference, they were examined at rest before performing two 15-minute bouts of exercise – one moderate and one high-intensity session on a treadmill. Their aerobic fitness levels were analysed during an incline challenge where the incline was increased by 2.5% every two minutes until the participants became too exhausted to continue.
The results illuminated that early birds used more fat for energy at rest and during exercise than night owls and were more sensitive to insulin. In contrast, night owls were insulin resistant, so their bodies needed more insulin to lower blood glucose levels, and their bodies also preferred carbohydrates as an energy source instead of fats. Night owls’ inability to respond to insulin can be harmful as it indicates a greater risk of type 2 diabetes and heart disease.
Professor Steven Malin, the senior author of the study from Rutgers University, concluded: “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.”
