Girls and young women who devote much time to the Internet, get too little sleep or regularly drink alcohol are more likely than their peers to put on excess weight, a new study suggests.

The researchers, who followed more than 5,000 girls between 14 and 21 years old for 1 year, found that the more spare time girls spent on the Internet, the more their body mass index (BMI) increased.

Similar patterns were seen when the researchers looked at alcohol consumption and sleep. In the latter case, lack of sleep was linked to greater gains in BMI - a measure of weight in relation to height.