Teenage boys who spend lots of time in front of the TV or computer screen are at risk of poorer bone health.
A study carried out in Norway found the same did not apply to girls, which it suggested could be explained by their different body fat distribution.
Researchers looked at how much time 15 to 18-year-olds said they spent sitting in front of screens at the weekend, with between four and six hours being the most common amount of time.
This was followed by more than six hours in boys and between two and four hours in girls.
One thousand school pup-ils' bone mineral density was analysed along with their height, weight and details of their lifestyles.
The team found that while girls in the four to six-hour category had the highest bone mineral density, the amount of time spent in front of screens had a negative effect on the bone mineral density of boys.
"Our study suggests persisting associations of screen-based sedentary activities on bone health in adolescence," the study authors said.
While time spent in front of the TV and computer games was linked to lower levels of physical activity, one in five of the girls and 26pc of the boys who said they spent more than four hours a day in front of a screen at the weekend also spent more than fours hours a week doing sport.
The study was led by the UiT Arctic University Norway in Tromso.