July 24 (HealthDay News) -- New moms who can't zip up their pre-pregnancy jeans might not be catching enough zzzs.
Getting a good night's sleep, in fact, may be just as important as diet and exercise for shedding baby weight.
One study of new mothers found that those who slept five or fewer hours a day six months after giving birth were three times as likely to hold onto those extra pounds as were women who got seven or more hours of sleep.
Short sleep duration "stood out as an independent risk factor" for weight retention, said Erica P. Gunderson, a research scientist and epidemiologist at Kaiser Permanente in Oakland, Calif., who worked on the study.
For many women, postpartum weight retention is a serious issue because it can lead to long-term weight gain. Some studies show that up to 20 percent of women retain at least 11 pounds at six to 18 months after giving birth, Finnish researchers reported.
Lifestyle factors that lead to postpartum weight retention -- including a woman's diet, physical activity and sleep patterns -- have not been well studied, researchers report. But as every bleary-eyed new mother knows, slumber is frequently disrupted or cut short in the first year after a baby's birth.
"Sleep deprivation can cause changes in the levels of hormones involved in appetite regulation," explained Dr. Sirimon Reutrakul, a clinical associate in medicine at the University of Chicago Medical Center.
"Keep in mind, though, that there are multiple factors involved in causing postpartum women to sleep less," she said. "These include just having a newborn, having other small children at home, possible postpartum depression, illness of the newborns, if any, work, etcetera," she said.
In Gunderson's study, the sleep and weight retention patterns of 940 Massachusetts women were analyzed. A year after giving birth, 124 of the women had retained 11 or more of the pounds they had put on during their pregnancy.
Short sleep duration was associated with a threefold higher risk of substantial weight retention, when compared with women who got seven hours of sleep. How long a woman breast-fed, however, was not a significant factor.
Dr. Truls Ostbye, a professor and vice chairman of research in the Department of Community and Family Medicine at Duke University Medical Center, is currently leading a study designed to promote weight loss in overweight women after childbirth. Preliminary data from that study show that "women who sleep less at six weeks lose less weight from six weeks to 12 months," Ostbye said.
But the relationship between sleep and weight loss isn't that simple. After adjusting for the fact that heavier women lose less weight and sleep less, "the effect of sleep on weight loss nearly goes away," he said.
"The relationship between obesity and sleep is there," he added, "but it is as likely that less sleep is a result of obesity as the other way around."
Advising women to get more sleep may not get to the root of their sleep-deprivation problem, Reutrakul said, "although stressing the importance of a good night's sleep is a good idea."
SOURCES: Erica P. Gunderson, Ph.D., research scientist and epidemiologist, Kaiser Permanente, Oakland, Calif.; Sirimon Reutrakul, M.D., clinical associate, medicine, Section of Endocrinology, University of Chicago Medical Center, Chicago; Truls Ostbye, M.D., Ph.D., M.P.H., professor and vice chairman, research, Department of Community and Family Medicine, Duke University Medical Center, Durham, N.C.; Nutrition Journal; American Journal of Preventive Medicine; American Journal of Epidemiology