Researchers looked at 1,088 pairs of twins in order to study the interaction between their genes and their sleeping habits and the subsequent effect on body mass index (BMI). They found that sleeping for less than seven hours a night was associated with increased BMI and greater genetic influences on BMI. Overall, the heritability of BMI (the proportion of variance attributed to genetic factors) was twice as high for twins who slept for less than seven hours as for twins who spent longer than nine hours asleep each night.
When asked to comment on the findings, principal investigator Dr Nathaniel Watson, from the University of Washington, said that short sleep may provide "a more permissive environment for the expression of obesity-related genes. Or it may be that extended sleep is protective by suppressing expression of obesity genes". That means that if two people carry the same gene that increases their susceptibility to weight gain, getting plenty of sleep at night could make all the difference in determining whether or not they will actually be overweight.
Of course, if you're trying to lose weight or maintain a healthy weight, your sleeping habits are not all you need to address. A healthy diet, with limited amounts of sugar, saturated fat and salt, as well as plenty of fruit and vegetables, is important for achieving an appropriate weight for your height. Additionally, you should try to take plenty of exercise, as this helps to create a healthy energy balance and will increase your chances of losing weight more quickly.