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'Night Owls' at Greater Risk of Diabetes Despite Late Morning Sleep

So-called “night owls,” people who stay up late and get up late in the morning, are at increased risk of developing diabetes compared to “larks,” or early risers. Researchers found this to be the case, even when the two groups spent the same number of hours asleep.

It doesn’t matter if they sleep the same number of hours. People who don’t go to bed until well after midnight develop more health problems than people who go to bed and wake up early.

That’s the finding of a new study by researchers in Korea.

It all has to do the with the body’s 24-hour clock, or circadian rhythm, according to Orfeu Buxton, a neuroscientist in the Division of Sleep Medicine at Harvard Medical School, who was not involved in the study.

“It prepares the body for certain functions at an appropriate time of day," said Buxton. "It turns out that eating in the morning is something that our body’s physiology seems to be ready for. And we tend to shut down in the later evening. So if we are eating then, that is the food that is more likely to cause metabolic problems or potbelly.”

The Korean researchers compared the health habits and metabolism of slightly more than 1,600 participants, ages 47-59. The group was divided according to their so-called chronotype or sleep-wake cycle.

About one-third of the participants were identified as morning chronotypes and 95 were classified as evening chronotypes. The rest of the participants were somewhere in the middle between very early risers and those who stayed up late.

The night owls had higher levels of body fat and fats in their blood and more muscle wasting than the larks, even though the evening chronotypes tended to be younger.

Buxton said people who do shift work, whose work hours start later in the day, were more likely to have the characteristics that put them at increased risk for diabetes.

“Some of the things that went with sleeping at a later time, in this sample in particular, were having a more sedentary lifestyle, not getting enough exercise, smoking and eating more of the day’s food later in the day," he said. "I mentioned before that breakfast is healthier than eating your food later in the day. Here they repeat that finding that we know.”

The study was published in the Journal of Clinical Endocrinology & Metabolism.