People who stay up later at night could be more at risk of developing type 2 diabetes and heart disease, according to a new study.
New research, by scientists at Rutgers University in New Jersey, found that "early birds" who go to sleep and wake up earlier have differently programmed body clocks which allow them to process fat easier.
Because these people are more active during the day, they use more fat as an energy source compared to those who rise later in the day - so for "night owls", fat builds up in the body easier.
This means there is a greater risk of developing diseases such as type 2 diabetes and heart disease, researchers in the US have suggested.
The study, which was published in the medical journal Experimental Physiology, examined 51 adults who were obese.
They were divided up into two groups - early birds and night owls - based on a factor called a chronotype, which is our body's natural desire to go to sleep and wake up at certain times.
The participants were then examined for a week, with researchers taking note of their activity patterns and how they used their energy whilst exercising and resting.
Also following a calorie-controlled diet and refraining from alcohol and caffeine, the participants had to fast for 10-12 hours overnight during the study.
The results showed that people in the early bird group burned more fat during exercise and rest than night owls, and that they were more sensitive to insulin. It also suggested that night owls relied more on carbs as a source of energy, rather than fat.
This means that people who stay up later need more insulin to lower their blood sugar levels, which puts them more at risk of developing diabetes.
It's not yet known what causes the shift in metabolic preference between early birds and night owls, but Professor Steven Malin, a senior author on the study, says it could be down to their sleeping times and circadium rhythms.
He told the Physiological Society : "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."
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