Researchers from Brigham and Women's Hospital in Boston found that either sleeping too little or sleeping "against" the body's biological clock increases a person's risk for becoming obese or developing diabetes. The research is published in the journal Science Translational Medicine.
Although the study was small, it is particularly valuable because -- unlike past studies that were only short-term or observational -- this study actually placed people in a controlled environment where researchers were able to change how long they slept and the time of day that they slept (similar to what shift workers might experience).
"We think these results support the findings from studies showing that, in people with a pre-diabetic condition, shift workers who stay awake at night are much more likely to progress to full-on diabetes than day workers," study researcher Orfeu M. Buxton, PhD, a neuroscientist at Brigham and Women's Hospital, said in a statement.
"Since night workers often have a hard time sleeping during the day, they can face both circadian disruption working at night and insufficient sleep during the day," Buxton added. "The evidence is clear that getting enough sleep is important for health, and that sleep should be at night for best effect."
The study included 21 people who were put completely in the hands of the researchers for almost six weeks. The researchers were able to control their diets, their activities and -- most importantly -- their sleep.
Everyone started out the study with 10 hours of sleep at nighttime, and then followed by a three-week period of getting just 5.6 hours of sleep a day, with people going to sleep at all different times of the day. Then, for the end the study, everyone had nine nights of normal sleep time at normal hours.
The researchers found that during the study period when the participants didn't get enough sleep and slept at odd times of the day, they had a decrease in their resting metabolic rate and they also had higher blood sugar levels after they ate (due to the pancreas having a worsened ability to secrete insulin, a risk factor for diabetes).
Extrapolated out, the researchers figured that these body changes could lead to an extra 10 pounds of weight gained each year (assuming people don't exercise more or change their diets to be healthier).