Too much TV for boys risks bone health
It's claimed teenage boys who spend too much time in front on the TV or on computers are risking poor bone health.
Researchers in Norway questioned 1,000 students, looking at how much time 15 to 18-year-olds spend sitting in front of screens at the weekend.
They found that boys spent more time than girls did, averaging around five hours a day at the weekend and just under four hours during the week.
The figures for girls showed four hours at weekends and just over three hours during the week.
The study, over a two year period, analysed the school pupils' bone mineral density, along with their height, weight and details of their lifestyles.
Results showed 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.
Report authors said: "Our study suggests persisting associations of screen-based sedentary activities on bone health in adolescence.
"This detrimental association should therefore be regarded as of public health importance and followed closely, since improvement of peak bone mass is possible."
Experts have not yet identified the cause of weaker bone health for boys.
But it is thought excessive sitting contributes to slowing down the metabolism.
This can affect our ability to regulate blood sugar and blood pressure, and metabolise fat - and may cause weaker muscles and bones.
Scientists said that while male adolescents reported longer hours sat watching TV, they are less likely to do anything else at the same time, which means they are often completely still.
It's thought girls tend to perform several activities at once, spending time in front of the TV or computers, as well as on their phones or carrying out other tasks, such as arts and crafts.
Dr Benjamin Jacobs, of the Royal College of Paediatrics and Child Health (RCPCH), said: " "This large important study adds further weight to the Royal College of Paediatrics and Child Health's drive to support paediatricians and others, to promote healthy lifestyles for young people in the UK.
"There are a number of ways they can do this - adequate exercise, screen time limited to less than four hours a day and appropriate vitamin D supplements to improve the bone health and general health of children in the UK."