Activity patterns and sleep cycles affect heart disease and type 2 diabetes

Wake/sleep cycles cause metabolic differences and change our body’s preferences for energy sources, according to new research published in Experimental Physiology.

Researchers from Rutgers University, New Jersey, USA found this out night owls have a reduced ability to use fat for energy, which means that fat can accumulate in the body and increase the risk of type 2 diabetes and cardiovascular disease. On the other hand, “night owls” (people who prefer to be active later in the day and at night) use less fat for energy at rest and during exercise.

Meanwhile, people who get up early who prefer to be active in the morning rely more on fat for energy and are more active during the day with higher levels of aerobic fitness than “night owls”.

The authors of the work classified the participants ( n = 51) into two groups (early and late) according to their “chronotype”, that is, 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- and nutrition-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 an incline challenge in which the incline was increased by 2.5% every two minutes until the participant reached the point of exhaustion.

More fat for energy

Early risers have been found to use more fat for energy both at rest and during exercise than night owls. The early risers were also more insulin sensitive. Night owls, on the other hand, were resistant to it, meaning their bodies needed more of it to lower blood sugar levels, and their bodies preferred carbohydrates for energy over fat. This group’s impaired ability to respond to insulin to promote fuel use can be detrimental, indicating an increased risk of type 2 diabetes and/or heart disease. The reason for this change in metabolic preferences between early risers and night owls is still unknown and needs further investigation.

The lead author, Prof Stephen Malin, from Rutgers University, New Jersey, USA, explained in this regard that “differences in fat metabolism between ‘early birds’ and ‘night owls’ indicate that our body’s circadian rhythm (wake/sleep cycle) can affect how our bodies use insulin.” A sensitive or impaired ability to respond to the hormone insulin has important health implications.”

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, the authors suggest that it could be used as factor for predicting individual risk of disease.

They also found that early risers were more active and had higher fitness levels than night owls, who were more sedentary during the day.

Finally, the authors of this work believe that more research is needed to investigate relationship between chronotype, exercise and metabolic adaptation to determine whether exercising earlier in the day has greater health benefits.