This research is by far the largest to track the effects of sleep habits on weight gain over a long period of time.
The study also found that lighter sleepers were 15% more likely to become obese compared with women who slept for seven hours a night and the researchers concluded that their findings had nothing to do with light sleepers eating too much, or not taking enough exercise.
Lead researcher Dr Sanjay Patel said: "That may not sound like much, but it is an average amount - some women gained much more than that, and even a small difference in weight can increase a person's risk of health problems such as diabetes and hypertension (blood pressure)."
"Prior studies have shown that after just a few days of sleep restriction, the hormones that control appetite cause people to become hungrier, so we thought that women who slept less might eat more.
"But in fact they ate less. That suggests that appetite and diet are not accounting for the weight gain in women who sleep less."
