Skimping on sleep, is unhealthy, but it doesn't make people fat, according to a new study.
"We hoped we were going to find good evidence for that," Dr. Diane S. Lauderdale told Reuters Health, "because it was such an interesting, intriguing, novel idea, with some reasons to think biologically it made sense. But we found nothing."
Chronic sleep deprivation is thought to be a risk factor for weight gain. While several studies have linked higher body mass index (BMI) to shorter nightly sleep, most have been cross-sectional, meaning they looked only at a single point in time — making it hard to prove whether sleeping too little leads to weight gain or vice versa, Lauderdale and her colleagues explain in the American Journal of Epidemiology.
Also, they say, most studies have relied on people's own estimations of how much they sleep at night, which are notoriously inaccurate.
To address this problem, Lauderdale, of the University of Chicago, and colleagues had people wear a wristwatch-like movement-tracking device called an actigraph, which can measure sleep duration as well as sleep fragmentation, or how often a person wakes up during the night.
They looked at 612 people participating in a long-running study of heart disease risk, all of whom were in their 40s.
While shorter sleep duration was indeed associated with higher BMI, as was more fragmented sleep, adjusting for ethnicity and socioeconomic status weakened the relationship.
And people who slept less at the study's outset were no more likely to gain weight during the five-year follow-up period.
Lauderdale and her team also found that the link between shorter sleep times and higher BMI was much weaker for people who did not snore, and much stronger for those who did.
"We were really surprised to find that the effect we were seeing in the whole study population was being driven by the very strong effect among the subset who snored," the researcher said in an interview. "We don't really know quite what it means."
Sleep apnea, in which a person wakes up gasping for breath several times during the night, has been linked to obesity, she added, but "snoring is not a very accurate marker of apnea."
While most people with sleep apnea snore, Lauderdale explained, not everyone who snores has sleep apnea. Snoring could be a particularly good indicator of apnea for heavier people, which might explain the findings, she added.
The findings need to be confirmed in other groups of people, the researcher said, and it would also be helpful to use a "good clinical diagnosis of apnea" to separate out those with a real sleep disorder from people who are simply snorers.
The new findings are "a major step forward for the field," Dr. Sanjay R. Patel of Case Western Reserve University in Cleveland, Ohio, writes in an editorial accompanying the study.
Research should now delve more deeply into the type of sleep people are getting, and whether this is influenced by BMI or vice versa, he adds.
SOURCE: American Journal of Epidemiology, October 1, 2009.