Night owls - the human variety, that is - are more prone to developing diabetes and other health issues than early-to-bed, early-to-rise types, a new study suggests.
And that's true even if they log the same number of hours of sleep when they do turn in, the researchers say.
The study in South Korea compared the chronotype - someone's natural sleep cycle - of people who stayed up late at night and then slept in with those who turned in at a more normal time and woke up earlier.
"Regardless of lifestyle, people who stayed up late faced a higher risk of developing health problems like diabetes or reduced muscle mass than those who were early risers," says endocrinologist Nan Hee Kim of the Korea University College of Medicine, lead author of the study appearing in the Journal of Clinical Endocrinology & Metabolism.
It may be the result of the tendency of night owls to experience poorer sleep quality and to more commonly engage in unhealthy behaviors such as late night snacking, smoking and a generally sedentary lifestyle, Kim says.
In addition, many night owls aren't getting sufficient sleep because they choose to stay up late but still have to wake up early for work, the researchers say.
The study analyzed the sleeping habits of 1,620 people, from ages 47 to 59, who participated in the Korean Genome Epidemiology Study.
They filled out questionnaires regarding their sleep-wake cycles, the quality of their nightly sleep, and information on their lifestyles, including exercise.
The researchers then took blood samples to gauge the participants' metabolic health, plus tests to measure body fat.
The researchers identified 480 participants as morning chronotypes, 95 as evening chronotypes, with the rest of the study participants falling somewhere between the two extremes.
Although generally younger, the evening chronotypes - the night owls - displayed elevated levels of fats in their body and bloodstream compared with the morning types, the researchers found.
They also showed a greater tendency to have a condition known as sarcopenia, in which the body slowly loses muscle mass, they reported.
People who stayed up late were 1.7 times more likely to have Type 2 diabetes, the researcher found, or high blood pressure, elevated blood sugar levels and abnormal cholesterol levels, which can increase a person's risk of cardiovascular disease or diabetes.
Because many younger people are night owls, "the metabolic risk associated with their circadian preference is an important health issue that needs to be addressed," Kim says.
While a person's circadian rhythm - their biological clock - is largely influenced by genetics, gender, age and their sleeping environment, it can be altered using internal or external cues such as light, exercise or eating behaviors, the researchers explain.