A Canadian study has shown that people who sleep for an average of 7-9 hours per night are less likely to put on weight than those who have very little or lots of sleep.

The in depth study, which was published in the April 2008 issue of Sleep magazine, took a sample of 276 adults between the ages of 21 and 64.

Those chosen to take part in the study were carefully selected to create a fair test. The participants reported their own sleep habits over a course of 6 years. Half of those chosen also had one parent and one child with at a body mass index (BMI) of at least 32.

BMI is a ratio of one’s weight in kilograms in relation to their height in meters squared. A ration between 18.5 and 25 is considered healthy, 25 to 30 is overweight, and over 30 is obese.

The sleep patterns were broken into three groups: short (5-6 hours), average (7-8 hours), and long (9-10 hours).

Jean-Philippe Chaput, MSc, of Laval University, Quebec City said: "Current treatments for obesity have been largely unsuccessful in maintaining long-term weight loss, suggesting the need for new insight into the mechanisms that result in altered metabolism and behaviour and may lead to obesity."

The results of the study showed that those who slept for a short period gained 1.98 kg more over a 6 year period, than those who had an average sleep, and generally those who slept for a long time gained 1.58 kg more. After 6 years, those who slept for long or short periods were more likely to gain 5 kg by 35% and 25% respectively.

These results also indicate the potential risk of obesity for those who do not sleep for an average length of time. Short sleepers are 27% more likely to become obese than average sleepers, and those who sleep for a long time have a 21% increased risk.

The study’s limitations include a small, non-random sample, use of self-reported questioners and not controlling for conditions such as breathing disorders during sleep, insomnia and depression that may affect normal sleep patterns.

The authors concluded that long and short sleeping times predict an increased risk of future weight and fat gain in adults and should therefore be considered as one of the factors that can lead to weight gain and obesity.

L.W.