Are you a night owl or a morning lark? Some people naturally gravitate to staying up late, and while genetics do play a major role in establishing your body clock, some research is suggesting later bedtimes could be bad for your health. A new large-scale observational study involving data from nearly half a million people has found that night owls have a 10 percent higher risk of dying sooner than those with a preference for getting to bed early.

The study tracked 433,268 subjects for six-and-a-half years. Aged between 38 and 73, the subjects were divided into four, self-reported categories: definite morning type, moderate morning type, moderate evening type, or definite evening type.

Even after adjusting for a variety of variables, including smoking, body mass index and pre-existing health ailments, the "definite evening type" was associated with a 10 percent higher risk of mortality than the "definite morning type." Night owls were also seen to have higher rates of diabetes and psychological or neurological disorders.

How to interpret these results is where the biggest debate of the study lies. A fascinating side detail noted in the paper was that the reported overall sleep duration between the different categories was similar. This means that those that went to bed later at night were still reporting the same overall amount of sleep as those going to bed early. This data point would eliminate the initial presumption that less sleep could be determining the differences in health effects between the groups.

"It could be that people who are up late have an internal biological clock that doesn't match their external environment," hypothesizes co-lead author Kristen Knutson. "It could be psychological stress, eating at the wrong time for their body, not exercising enough, not sleeping enough, being awake at night by yourself, maybe drug or alcohol use. There are a whole variety of unhealthy behaviors related to being up late in the dark by yourself."

One interesting idea raised in the paper is the proposal that night owls have a higher morbidity rate due to greater exposure to artificial light and, as a result, lower levels of melatonin. It's a compelling hypothesis, backed up by some research linking low levels of melatonin to higher rates of diabetes and some cancers.

The research team is now looking forward to further study that will try to find out if shifting night owls to earlier sleep schedules results in overall health improvements. The big question is whether many of the negative health effects associated with night owl behavior are simply due to the fact that the world is more set up for morning types, and those night behaviors simply clash with social realities and work shifts.

"If we can recognize these chronotypes are, in part, genetically determined and not just a character flaw, jobs and work hours could have more flexibility for owls," says Knutson. "They shouldn't be forced to get up for an 8 a.m. shift. Make work shifts match peoples' chronotypes. Some people may be better suited to night shifts."

Knutson and the team suggest several tips for night owls that could help optimize their health, including regimented bed times, better awareness of negative nighttime lifestyle behaviors (such as late-night eating), and trying to get exposure to as much morning and daylight as possible.

The study was published in the journal Chronobiology International.

Source: Northwestern University via EurekAlert