As part of the Integrative Cardiac Health Project at Walter Reed Army Medical Center, researchers analyzed the sleep, activity and energy expenditures of 14 nurses who had volunteered for a heart-health program at the Walter Reed, where the nurses were employed. The program included nutritional counseling, exercise training, stress management and sleep improvement.
Each participant wore an actigraphy armband that measured total activity, body temperature, body position and other indices of activity and rest.
"When we analyzed our data by splitting our subjects into 'short sleepers' and 'long sleepers,' we found that short sleepers tended to have a higher BMI, 28.3 kg/m2, compared to long sleepers, who had an average BMI of 24.5. Short sleepers also had lower sleep efficiency, experienced as greater difficulty getting to sleep and staying asleep," said lead investigator Arn Eliasson, M.D.
Surprisingly, overweight individuals tended to be more active than their normal weight counterparts, taking significantly more steps than normal weight individuals: 14,000 compared to 11,300, a nearly 25 percent difference, and expending nearly 1,000 more calories a day—3,064 versus 2,080.
However, those additional energy expenditures did not manifest in reduced weight.
"We found so many interesting links in our data. It opens up a number of possibilities for future investigation," said Eliasson. "Primarily, we want to know what is driving the weight differences, and why sleep and weight appear to be connected."
He postulates that getting less sleep might disrupt natural hormonal balances—for example, reducing the amount of leptin, otherwise known as the satiety hormone—and could thereby cause those individuals to eat more. Stress may also play a role in both reducing the length and quality of sleep and increasing eating and other behaviors that may result in weight gain.
"Higher perceived stress may erode sleep. Stress and being less rested may cause these individuals to be less organized than normal weight individuals, meaning they would have to make more trips and take more steps to accomplish the same tasks. This might add to their stress and encourage other unhealthy behaviors like stress eating," said Dr. Eliasson.
"It would be fascinating to know the results of a carefully designed study that controlled for the many influences on weight gain, while varying sleep parameters and measuring hormonal mediators of appetite and metabolism," said Dr. Eliasson. "We are planning further studies to evaluate the role of stress in sleep and metabolism."