How Screen Time Might Affect Teenage Bones

Bone density in teenage boys may decrease with excessive screen time

(RxWiki News) Some teens act like they can't live without their phones, tablets or computers. But parents may be wise to set screen-time limits.

A new study from Norway found that increased time spent on screen-based activities may be tied to decreased bone density in teen boys.

"Our study suggests persisting associations of screen-based sedentary activities on bone health in adolescence," wrote lead study author Anne Winther, PhD, of the Arctic University of Norway, and colleagues. "This detrimental association should therefore be regarded as of public health importance and followed closely, since improvement of peak bone mass is possible."

Dr. Winther and team studied nearly 1,000 teen boys and girls between 2010 and 2011. All of these boys and girls were between 15 and 17 years of age. A follow-up occurred two years later, when these researchers studied nearly 700 of these patients.

The teens were asked to fill out surveys about their overall screen-based activity and their physical activity during weekdays and weekends. These patients also had their bone density measured at the hip, the thigh and over the entire body.

Dr. Winther and team found that, on weekends, the boys spent more time in front of screens (an average of five hours daily) than girls (an average of four hours daily).

These researchers also found a link between the amount of screen time and the amount of physical activity. As the number of hours of screen time increased, both boys and girls were more likely to be sedentary.

During the initial study, Dr. Winther and team found a link between screen time and an overall decrease in these boys' bone density. This link remained during follow-up two years later, although the link was weaker.

There was no link found between screen time and loss of bone density in girls during the initial study and the follow-up.

“These conflicting results may be related to different factors, as the relationship between fat and bone varies with age and hormones,” Dr. Winther and colleagues wrote.

According to Dr. Winther and team, lowering the amount of time spent in front of screens and upping physical activity may be key to maintaining healthy bone density in teens.

"The relevance of international guidelines’ recommendation of no more than 2 [hours] screen time a day for children and adolescents ... should be discussed thoroughly and compared to the importance of physical activity for bone health," Dr. Winther and colleagues wrote.

This study was published online June 10 in the journal BMJ Open.

The Northern Norway Regional Health Authority funded this research. No conflicts of interest were disclosed.

Review Date: 
June 10, 2015