Night owl sleep pattern puts you at risk

Are you an early bird or a night owl? Our activity patterns and sleep cycles can influence our risk of developing diseases, such as type 2 diabetes and heart disease. New research published in Experimental Physiology finds that wake/sleep cycles cause differences in metabolism and alter the body’s preference for energy sources. Researchers have found that those who spend time late have a reduced ability to use fat for energy, which means that fat may build up in the body and increase the risk of type 2 diabetes and cardiovascular disease.

The metabolic differences related to how well each group was able to use insulin to enhance cells’ uptake of glucose for storage and energy use. People who are “early birds” (individuals who prefer being 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 “night owls”. On the other hand, people who prefer to be active later in the day and night use less fat for energy at rest and during exercise.

Researchers from Rutgers University, New Jersey, USA categorized participants (n = 51) into two groups (early and late) based on a ‘temporal pattern’ – our natural tendency to seek activity and sleep at different times. They used advanced imaging to assess body mass and 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 reduce the nutritional impact on results. To study fuel preference, they were tested at rest before completing two 15-minute bouts of exercise: a moderate session and a high intensity session on the treadmill. Aerobic fitness levels were tested with an incline challenge in which the incline was raised 2.5% every two minutes until the participant reached the point of exhaustion.

Researchers have found that early birds use more fat for energy at rest and during exercise than night owls. Early birds were also more sensitive to insulin. Night owls, on the other hand, are insulin resistant, which means that their bodies require more insulin to lower blood sugar levels, and that their bodies prefer carbohydrates as an energy source over fats. The ability of this poor group to respond to insulin to enhance fuel use can be detrimental as it indicates an increased risk of type 2 diabetes and/or heart disease. The reason for this shift in metabolic preference between early birds and night owls is not yet known and needs further investigation.

Senior author Professor Stephen Malin, Rutgers University, New Jersey, USA said:

“Differences in fat metabolism between ‘early birds’ and ‘night owls’ show that the body’s circadian rhythm (wake/sleep cycle) can influence how our bodies use insulin. Sensitive or impaired ability to respond to the hormone insulin has major implications for our health.” This observation advances our understanding of how circadian rhythms affect our health. Because temporal pattern appears to influence our metabolism and hormone functioning, we suggest that temporal pattern can be used as a predictor of an individual’s disease risk.”

“We also found that early birds are more physically active and have higher levels of fitness than night owls who are more active throughout the day. Further research is needed to examine the link between chronotype, exercise and metabolic adaptation to determine whether exercise earlier in the day It has even greater health benefits.”


  1. Full research title: Early temporal pattern with metabolic syndrome favoring rest and fat oxidation exercise in relation to insulin-stimulated non-oxidative glucose disposal. link to paper https://physoc.onlinelibrary.wiley.com/doi/abs/10.1113/EP090613
  2. Experimental Physiology publishes research papers that provide new insights into homeostatic and adaptive responses in health, as well as those that advance our understanding of pathophysiological mechanisms in disease. https://physoc.onlinelibrary.wiley.com/hub/journal/1469445X/aims-and-scope/read-full-aims-and-scope
  3. The Physiological Society includes more than 3,000 scientists from more than 60 countries. The Society promotes physiology with the public and Parliament alike. It supports physiologists by organizing global conferences and providing grants for research and also publishes the latest developments in the field in its three leading scientific journals, Journal of Physiology and Experimental Physiology and Physiological Reports. www.physoc.org.
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