Watching a lot of television during childhood and adolescence may affect bone health later in life, a new study has found.

Until now, the effects of watching television on skeletal health have been unclear, but according to these findings, those who consistently watched television in early life had a lower peak bone mass at the age of 20.

Bone mass refers to the amount of bone tissue in the skeleton and this can keep growing until the age of 30, when it reaches what is known as peak bone mass. However, up to 90% of peak bone mass is reached in girls by the age of 18 and in boys by the age of 20.

The higher the peak bone mass the better because a loss of bone mass, which generally occurs as we age, increases the risk of osteoporosis.

Researchers recorded the amount of television watched per week by almost 1,200 young people at the ages of five, eight, 10, 14 17 and 20.

The study found that those who consistently watched more than 14 hours of television per week had lower bone mineral content at the age of 20 compared to those who watched less television.

These results stood even when other factors were taken into account such as calcium intake, vitamin D levels, body mass index and smoking.

"Consistently high TV watching during childhood and adolescence independently predicted reduced peak bone mass at age 20 years. Since attainment of optimal peak bone mass is protective against osteoporosis later in life, reducing sedentary time in children may have long-term skeletal benefits," the researchers concluded.

Details of these findings are published in the Journal of Bone and Mineral Research.