Sleep more than 8 hours to stay slim
Adding a few hours sleep to your night may prevent you from gaining weight.
A new study has found that sleeping more than nine hours a night appears to suppress genetic factors that lead to weight gain.
In contrast, getting too little sleep seems to have the opposite effect.
Previous research has shown an association between poor sleep and obesity, but the new findings reveal a complex interaction between sleep and genetic factors linked to body weight.
Scientists made the discovery after studying 1088 pairs of identical and non-identical twins.
Twin studies help researchers unravel genetic and environmental influences. Only identical twins share the same genes, and are therefore subject to the same genetic effects, so differences between them are likely to be due to environmental factors.
The study found heritability of body mass index (BMI) - a measurement relating weight and height - was twice as high for short than for long sleepers.
For twins sleeping less than seven hours a night, genetic factors accounted for 70 per cent of differences in BMI. In twins averaging more than nine hours' sleep, only 32 per cent of weight variations could be attributed to genes.
''The results suggest that shorter sleep provides a more permissive environment for the expression of obesity related genes," WAtoday quoted Nathaniel Watson, from the University of Washington, who led the US study, as saying.
''Or it may be that extended sleep is protective by suppressing expression of obesity genes," he stated.
The scientists suggested hectic modern western lifestyles might contribute to obesity.
''Modern society with its ubiquitous technology often can cause misalignment between sleep need and sleep actualisation. This frequently has adverse consequences for cognitive (mental) function and metabolic, cardiovascular, and immunologic health," they wrote.
''Indeed, over the past century habitual sleep duration has dropped 1.5 hours per night and since 2001 the percentage of US adults getting at least eight hours of sleep per night on weeknights has fallen from 38 per cent to 27 per cent.
''Evidence is mounting that chronically reduced sleep times are associated with obesity," they added.
Sleep may influence weight by affecting hormones, glucose metabolism and inflammation, they said.
Some studies have associated long sleep duration with heart disease, insulin resistence (a precursor to diabetes) and early death.
''We did not observe this in our sample, but our sample is much younger than those used in studies that established these adverse associations,'' the researchers noted.
The findings were published on Monday in the journal, Sleep.