By Don Rauf
Going to sleep late at night may have a significant negative impact on your health. A new study has found that “night owls” who head to bed late and wake late face a much greater chance of developing diabetes than “early birds.”
In an analysis involving more than 63,000 subjects published September 12 in the Annals of Internal Medicine, “evening people” had a 72 percent greater risk of diabetes. They were also more likely to drink alcohol in higher quantities, have a low-quality diet, get fewer hours of sleep per night, and be current smokers. In addition, their weight, BMI, and physical activity rates were more likely to be in an unhealthy range.
“Overall, the night owls were 54 percent more likely to have an unhealthy lifestyle compared to the early birds,” says the lead study author, Sina Kianersi, PhD, a postdoctoral research fellow at Brigham and Women’s Hospital and Harvard Medical School in Boston. “After we account for health factors such as weight, physical activity and diet, however, their diabetes risk drops from 72 percent to 19 percent. This means that much of the increased risk is due to their unhealthy habits.”
Sleep Habits Themselves May Affect Health Risks
The 19 percent greater diabetes risk due to unhealthy habits is still significant, however, according to Dr. Kianersi. The result suggests that other factors, such as sleep patterns themselves and their effect on metabolism and hormones, may contribute to diabetes risk.
For Sun Kim, MD, an endocrinologist and an associate professor of medicine at Stanford Medicine in California, the findings support previous research showing a link between sleep itself and health outcomes.
“Short sleep duration and/or sleep deprivation [for example] have been associated with increased diabetes risk,” says Dr. Kim, who was not involved in this study. “Although mechanisms are still being investigated, short sleep may increase hormones for appetite and stress and increase inflammation, which can lead to insulin resistance, a known mechanism to worsen glucose control.”
Kianersi adds that his team intends to explore how genetics may help explain this higher risk.
“Recent discoveries actually show that there are more than 350 genetic markers or genetic signs in our DNA that can make us a night owl or an early bird,” he says. “We really want to understand what is the mechanism that increases the risk among night owls even after accounting for their unhealthy habits.”
How Sleep Preferences Make a Difference
For this study, scientists sought to understand how sleep preferences may influence diabetes risk. Every person has a natural inclination for when they prefer to sleep called a “chronotype.” Your chronotype may be early-to-bed, early-to-rise; late-to-bed, late-to-rise; or somewhere in between.
Chronotypes are influenced by genetics and driven by circadian rhythms, the body’s natural processes that are guided by light and dark during a 24-hour period.
Kianersi and his team looked at data from 63,676 female nurses (ages 45 to 62) who self-reported their chronotype and health factors, including diet quality, weight and body mass index, sleep timing, smoking behaviors, alcohol use, physical activity, and family history of diabetes.
The participants, who were followed for eight years, had no history of cancer, cardiovascular disease, or diabetes at the study starting point in 2009.
Just over 1 in 10 of the participants reported having a “definite evening” chronotype, and about 35 percent reported having a “definite morning” chronotype. The remaining population, around half, were labeled as “intermediate,” meaning they identified as neither a morning nor an evening type or as being only slightly more one than the other.
Study authors noted that among participants with the healthiest lifestyles, only 6 percent had evening chronotypes, while among those with the unhealthiest lifestyles, 25 percent were evening chronotypes.
They also found the association between evening chronotype and diabetes risk only in those nurses who worked day shifts and not those who worked overnight shifts.
The authors theorize that this association may be due to work schedules that do not align with a person’s chronotype. The increased diabetes risk, then, may be explained by a mismatch between chronotype and work timing rather than the chronotype itself.
“A potential solution to this could be for individuals to work schedules that align with their personal chronotype to promote a healthier lifestyle,” says Lauren Amaya, PhD, a teaching associate professor and diabetes specialist at Oklahoma State University in Stillwater.
If evening chronotypes are allowed to sleep and wake closer to their circadian clock — for example, by working an evening shift rather than a morning shift — this may lead to a more consistent schedule that better matches their circadian sleep-wake timing, adds Fiona Barwick, PhD, an associate professor of psychiatry and behavioral sciences specializing in sleep medicine at Stanford Health Care in Redwood City, California.
“This may in turn lead to less ‘shift work,’ more sleep, less need for sleep aids, more appropriate meal timing, and a healthier diet — all of which would reduce risk to cardiometabolic health,” says Dr. Barwick.
Change Lifestyle Habits to Lower Risk
While people may be genetically hardwired to be night owls or early birds, the researchers suggest that “evening people” can still take steps to improve the unhealthy habits that raise diabetes risk, such as modifying their diet, losing weight, exercising more, reducing drinking, and quitting smoking.
Dr. Amaya, who was not involved in this research, points out that the study was limited in that it included primarily middle-aged white female nurses with a relatively high level of education and socioeconomic status who did shift work in hospitals.
“It would be interesting to replicate this study with other populations of individuals, such as men, nonwhite racial and ethnic groups, and those from lower socioeconomic statuses, all of which are factors associated with an elevated type 2 diabetes risk,” she says.