Teenage girls who are too thin may face major problems with their bones, including osteoporosis, new research indicates. It is already known that the amount of muscle in the body is related to bone growth. However these new findings show that fat mass is also important for the building of bones, particularly in girls.

The findings come from the ‘Children of the 90s’ project, an ongoing health research project being carried out by the University of Bristol. More than 14,000 pregnant women enrolled in the study in the early 1990s and the health and development of their children has been followed in detail ever since.

Over 4,000 young people aged 15 took part in this latest study. Sophisticated scanning techniques calculated the shape and density of their bones, as well as how much body fat they had. Those with higher levels of fat tended to have larger and thicker bones.

This was particularly marked in the girls of the study. For example, in girls, a five kilogram increase in fat mass was associated with an 8% increase in the circumference of the tibia – one of the lower leg bones. As girls tend to have higher levels of fat than boys, even when they are at a normal weight, these findings suggest that fat plays an important role in female bone development.

The researchers emphasised that building strong bones in the early years is particularly important for females, as they are three times more likely to develop osteoporosis. Women also suffer two to three times more hip fractures than men.

“There is a good deal of pressure on teenage girls to be thin, but they need to be aware that this could endanger their developing skeleton and put them at increased risk of osteoporosis,” commented lead researcher, Prof Jon Tobias.