Calcium and Bone Density in Adolescents
Supplementing with calcium during the time of rapid growth that occurs around puberty can have a small beneficial effect on bone density three to four years later, and might therefore help prevent osteoporosis in later life, suggests a pair of studies in the American Journal of Nutrition (2005;81:168–74 and 175–88).
Preventing osteoporosis, a condition characterized by low bone density and increased risk of bone fracture, is currently approached in two ways: maximizing bone density at the time in life when it reaches its peak (about 25 years old) and minimizing bone loss after menopause. A number of nutrients can influence bone density by stimulating proper use of calcium by the body; however, adequate calcium intake and exercise remain the cornerstones of osteoporosis prevention. The effect of calcium supplementation in preventing bone loss after menopause is well established.
It has been suggested that increasing calcium intake during the growth spurt that occurs around puberty might increase the peak bone density in young adulthood. Several studies have found that children and adolescents who supplement with calcium lay down more bone during the time of growth around puberty than those who don’t, but a lasting effect on osteoporosis risk in adulthood has not been demonstrated.
In the first of the two studies, 354 girls between ages 8 and 13 who were consuming less than 1,480 mg of calcium per day were randomly assigned to receive either 1,000 mg of calcium per day (from calcium citrate-malate) or placebo for four years. Physical exams and bone density measurements were done every six months, and diet and exercise questionnaires were given at these visits. The average amount of calcium eaten in food was found to be 830 mg per day over the course of the study; because the girls taking supplements used an average of 66% of the amount they were asked to take, their total calcium intake was boosted to about 1,500 mg per day. The girls who received calcium had significantly higher bone density than the girls who received placebo after four years. A three-year extension of the study enlisted 187 of the original participants. They continued to take their assigned calcium or placebo. At the end of this extension, the beneficial effect of calcium was statistically significant in the hand bones, as well as the forearm bones of tall girls and those with the highest calcium intake (averaging 1,353 mg per day), but not in the wrist bones nor in total body bone density.
In the second study, 96 girls participated in a follow-up study that took place several years after a one-year trial on calcium supplements and bone density. The participants were adolescent girls who had begun having menstrual cycles before entering the study and had low dietary calcium intake (less than 800 mg per day). They were first randomly assigned to receive either 1,000 mg of calcium per day (from calcium carbonate) or placebo for one year. At the end of that trial, girls taking calcium had had significantly greater increases in bone density than girls receiving placebo. In the follow-up study, bone density was measured about three and a half years after supplementation ended and was compared with measurements from the beginning of the original study. The increase in bone density continued to be greater in the girls who had received calcium than those who had received placebo, but this difference was only statistically significant in a subgroup of girls who had taken at least 75% of the supplemental calcium they had been asked to take.
The results of both studies suggest that calcium supplementation in girls who are near the onset of puberty might have a lasting benefit on bone density. This effect was noted both in the case of girls continuing to take calcium and in girls who stopped. Long-term studies are needed to determine whether calcium supplementation at puberty affects peak bone density, which typically occurs 10 to 15 years later.
Maureen Williams, ND, received her bachelor’s degree from the University of Pennsylvania and her Doctorate of Naturopathic Medicine from Bastyr University in Seattle, WA. She has a private practice in Quechee, VT, and does extensive work with traditional herbal medicine in Guatemala and Honduras. Dr. Williams is a regular contributor to Healthnotes Newswire.
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