Exercise, not calcium, may have the strongest effect on growing bones in adolescent girls. In a decade-long study, researchers from the Penn State University College of Medicine in Hershey, USA, found that calcium intake was not related to bone growth or bone strength in young women. But, physical exercise was related to stronger bones and has been found to be the most important modifiable determinant of bone development for young women. At least 15 per cent of the variation in bone strength seen among healthy women can be attributed to exercise. Exercise is also the most important influence on bone development in young men, too. Despite the apparent importance of exercise, teens should not skimp on calcium-rich foods. Parents should continue to encourage teens to consume low-fat dairy products since they are convenient and are wonderful sources of nutrients, minerals and vitamins. The study included 80 young women who were followed for 10 years. When the study began, the girls were around 12 years old, and none had begun menstruating. One of the study's goals was to measure the effects of calcium intake, exercise and oral contraceptives on bone health. The participants of this study were followed for over a decade, with measurements made every 6 months for the first 4 years and yearly thereafter. The study found that the calcium intake, which ranged from 500 milligrams (mg) to 1,900 mg per day, was not significantly associated with bone growth or bone density. The study also showed that the use of oral contraceptives was not related to bone health. Despite some research that has found that women on oral contraceptives have thinner bones, young women who had taken the pill had just as healthy bones as those who had not taken oral contraceptives. But exercise had a direct relation with bone health. The more a teen girl participated in sports, the stronger were her bones. The results of the study support other research showing that exercise during the teen years can have a significant effect on bones. Regular load-bearing exercise, like walking 30 minutes a day, has a positive effect on bone development. Although the brittle-bone disease osteoporosis does not usually strike until late in life, the teen years are an important time for bone development. In fact, girls form 40 per cent of their bone mass during adolescence.
Journal of Pediatrics,
June 2004