Teen sport protects bones
“Playing ball games as a teenager can cut the chances of going on to suffer from brittle bones,” says The Daily Telegraph. The newspaper says weight-bearing sport strengthens the bones and keeps them healthy for a further 40 years.
The newspaper’s claims are based on a Japanese study on 46 post-menopausal women. Researchers asked the women to recall what types of exercise they did during adolescence and compared the results to bone scans. They found that women who had performed weight-bearing sports had a higher mineral content in their bones.
This size and design of this study mean it cannot prove that exercise has caused the differences in the womens’ bones. There are many other factors that might be responsible for improving bone health including diet, that the researchers did not take into account when analysing their data.
However, apart from the risk of injuries that can occur during ball sports (and other vigorous exercise), it seems sensible to suggest that weight bearing exercise can improve bone strength and many other aspects of health.
Where did the story come from?
This research was conducted by Dr T. Kato and colleagues from Suzuka University of Medical Science, the Japan Institute of Sports Sciences and Chukyo University in Japan. Their work was funded by the Japanese Ministry of Education and Sciences.
The study was published in a peer-reviewed medical journal, the British Journal of Sports Medicine .
What kind of scientific study was this?
This was a cross sectional study in which 46 post-menopausal women were asked what sports they participated in between the ages of 12 and 18 years. From their responses, they were grouped as either participating in weight-bearing sports or not.
The health of the women’s bones was assessed by measuring bone mineral density (BMD) in their lower back and hip regions. This was done using a painless, non-invasive scan. They also measured the area and the perimeter of the mid thigh bone.
Researchers then compared the BMD and other bone measurements between the two exercise groups and discussed any differences.
What were the results of the study?
The researchers report that those in the weight bearing group had significantly greater bone mineral density in the lumbar spine (lower back) and femoral neck (hip) than those women in the non-weight bearing sport group.
What interpretations did the researchers draw from these results?
The researchers conclude that their results suggest that weight-bearing activities during adolescence can affect bone structure and that these effects may be preserved for up to 40 years.
What does the NHS Knowledge Service make of this study?
This is a very small study with several shortcomings including its design. As it was a cross sectional study, it cannot prove causation (that one thing causes another). Many other factors, aside from what sport the women did when they were young, may play a part in bone health.
Shortcomings to note about this study:
Although the researchers collected information on diet (albeit post-menopausal diet) and other information such as smoking status, medication, fracture history and bone disease, they do not use this information in their analysis, taking into account only age and weight of the women.
The questionnaire asked about sporting habits 40 to 60 years previously and it is possible that memory of such activities differs between women who are healthier compared to those who are not. This would have introduced bias into the study.
- Although there are several features of the two groups of women that are broadly similar at the start, for example age, height, weight, calcium and years since menopause, the researchers do not describe the women in terms of other risk factors, for example smoking.
- The difference in bone density was reported as a difference in grams rather than as the more usual T score, which gives an indication of the strength of bones relative to healthy, young women.
The study essentially compared bone characteristics between 16 women who reported participating in ‘weight-bearing sports’ in their youth with 30 who had not. The association that was found is not surprising as participation in vigorous activity may just mean that they generally have better health. The design and analyses of this study cannot prove this.
Many factors are involved in bone health, including genetics, diet (importantly calcium intake) and lifestyle. This study advocates participation in sports when young, which is no bad thing given that the benefits of exercise on health throughout life are well known.
