Screen time linked to weaker bones

June 24, 2015

Topic: orthopaedic injury

Spending a lot of time in front of a screen is not doing any favors for adolescents' bone health.

Spending a lot of time in front of a screen is not doing any favors for adolescents' bone health. Researchers from Arctic University collected data as part of the Tromso Fit Futures Study in Norway. The findings revealed that girls may have a little bit of an advantage over adolescent boys, who were found to have weaker bone density. The findings were published in the journal BMJ Open.

A question of lifestyles
The researchers believe that young women may have a higher bone density than men because their fat distribution is different, protecting the bones better. The study authors examined 961 adolescents between the ages of 15 and 17 in 2011. Two years later, they checked in with 688 of these individuals. The researchers asked the participants several questions about their lifestyle, including whether they smoked and drank, how much time they spent on the computer or watching television, and what they ate on a weekly basis. The study authors were hoping to discover whether nutrition had any impact on bone growth and orthopaedic injuries. Certain beverages, such as milk, can benefit the bones. Others, such as soft drinks, can weaken them.

The questionnaire also asked about regular physical activity and how frequently the teens exercised. The researchers categorized the activity into their amount of sitting, walking, cycling and their time dedicated to intense workouts and recreational sports. They measured the adolescents' bone density in a few different places: the hip, the thigh bone and the average for the whole skeleton. Participants' height and weight were measured too. 

"The men had greater bone density loss than women, especially if they spent a lot of time sitting on the weekends."

Making comparisons
Overall, the results revealed that boys spent more time in front of screens than girls. During the week, boys would spend an average of four hours each day in front of some type of screen. On the weekends, they spent five hours a day in front of a screen. Comparatively, girls spent about three hours in front of some sort of screen during the week and four hours on the weekend. Yet the data was not as simple as it appeared. The participants who were more sedentary on the weekends were actually more active during the week, investing about four hours into recreational sports or intense exercise.

Regardless, the data indicated that men had greater bone density loss than women, especially if they spent a lot of time sitting on the weekends. Adolescent girls who were less active during the weekends only had weaker bones at the femoral neck, or the thigh bone. The findings also showed that the more time spent in a chair or on a couch, the greater the bone density loss was. If boys spent two hours or less sitting at a screen over the weekend, their femoral bones were stronger. 

Conversely, the greater amount of screen time gave girls a higher bone density. Girls who spent between four and six hours in front of a screen during the weekend had a higher bone density, and girls who were more active actually had a lower bone density. 

The researchers found all of the same data two years later. So why were the results so different? The study authors noted it may have something to do with differences in hormone amounts and fat distribution between boys and girls. 

One 2014 study examined the relationship between body weight and bone density in women and discovered that lean mass may actually be able to protect the bones from weakening. However, if the weight becomes too great, it could weaken women's bones. The findings were published in the International Journal of Preventative Medicine. So, if active teen girls with relatively lean mass are sedentary on the weekends, it may not hurt their bones as much as boys. 

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