A study published in the American Journal of Clinical Nutrition (January 2005 81(1):168-174) shows that teenage girls who take calcium supplements for only a year can effect increases in bone mineral density for years afterward. It is widely recognized that calcium is necessary for strong bone formation. However, what is unique to this study is that once discontinuation of the supplement occurs, the effect can last up to 3.5 years. The importance of strong bones is seen later in life when osteoporotic fractures become a major cause of morbidity. Research has shown that building a peak bone mass early in life is the best preventative factor in osteoporosis (first three decades). Limiting bone loss after menopause is also important.
Previous studies have shown that calcium supplementation in postmenarcheal girls, who have low calcium intakes, can indeed increase bone mineral density. However, there have been conflicting studies on whether this effect is sustained once supplements are withdrawn. In the present study, researchers followed up ninety seven girls who had taken part in a prior intervention study where they had been divided into two groups: one given 1000mg supplements of calcium and one given placebo for 1 year. The follow-up took place 3.5 years after the termination of the initial intervention study.
The results showed that the calcium-supplemented group tended to have a greater accretion of total-body bone mineral density (TBBMD) than did the control group. The researchers point out that there was no additional accretion of bone mineral density after the supplementation ended. They also state that, "Longer-term calcium-supplementation studies in adolescents are necessary to confirm whether high calcium intakes can improve peak bone mass." Nevertheless, this is an important study highlighting that calcium does indeed have long-term effects on bone, lasting at least >3 years.
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