Scientific Study Proves: Researchers Guess 99% of the time,

Published: Tuesday, April 1, 2008 | 12:24 AM ETCanadian Press: Helen Branswell, THE CANADIAN PRESS

TORONTO - People interested in holding or reaching a healthy weight might want to apply a lesson from Goldilocks when it comes to how much sleep they get.

A new study suggests there is a just right amount of sleep, with people who get too little and those who get too much actually putting on weight as a consequence.

The study, conducted by obesity researchers at Laval University in Quebec City, showed that people who slept five to six hours a night and people who averaged nine to 10 hours a night put on more weight when followed over a six-year period as compared to people who got the recommended seven to eight hours of shut-eye.

The study, published Tuesday in the journal Sleep, fits with a number of recent scientific articles that suggest a U-shaped relationship may exist between sleep duration and body mass index, the height-to-weight measure used to differentiate between healthy and unhealthy weights.

"Everything that we've seen in the last few years regarding this issue says yes, if you're getting seven to eight hours of sleep at night, you have the best chance of not gaining weight and maintaining your own weight," said Donna Arand, an experimental psychologist with the Sleep Disorders Center at Kettering Hospital in Dayton, Ohio.

"And if you're getting a lot less than that or a lot more than that, you're hurting yourself and it's going to be an uphill battle."

The Laval researchers followed 276 adults aged 21 to 64 years who were enrolled in the Quebec Family Study. More than half were drawn from families where at least one parent and one offspring were obese by BMI measures.After the researchers adjusted for age, gender and BMI levels at the start of the study, short sleepers and long sleepers were more likely to gain weight over the six-year period.Short sleepers gained an average of 1.98 kilograms more than average sleepers and long duration sleepers gained an average of 1.58 kilograms when compared to the optimal length sleepers.

The study cannot provide definitive answers to why those who were getting too little or too much sleep were more likely to gain weight.But senior author Angelo Tremblay, who holds a Canada Research Chair in physical activity, nutrition and energy balance, said the thinking is that sleep deprivation disrupts the production of hormones that regulate the body's appetite. Too little sleep appears to increase production of ghrelin - the hormone that tells us we're hungry - and decrease production of leptin, the hormone that tells us we're full."So if there is an increase in the hormone that is known to increase appetite you expect also an increased hunger level," he said from Quebec City.

Why then would too much sleep produce the same problem as too little? Tremblay said some researchers believe long sleepers are actually bad sleepers - that they stay in bed for longer because they haven't had high quality sleep.Arand, who was not involved in the study, said this type of work suggests that sleep management should play a role in weight management - though she admitted the world's dieting woes won't be solved by telling people to aim for optimal sleep times."It's not as easy as just doing that," said Arand, who is a spokesperson for the American Academy of Sleep Medicine."But I think that is a major component of it. If you're not getting enough sleep, everything else you're doing is working against your body's other desire, to eat more and increase caloric intake."

Tremblay said that while in theory more sleep should lead to better weight control, one would need to figure out why these people aren't sleeping the right amount in the first place. "For many people, they are not choosing to be short sleepers.""OK, there are probably some individuals who are working so hard they're cutting in on their sleep time. But there are others for whom sleep duration is a real problem," he said.