Effect of a calcium and exercise intervention on the bone mineral status of 16-18-y-old adolescent girls.

Four-group intervention study in healthy 16 to 18-year-old female students from two sixth-form colleges in Cambridge, United Kingdom. A total of 131 of 144 recruited participants completed the study; baseline group characteristics were not significantly different.

Active calcium-supplemented participants received 1000 mg/day elemental calcium as calcium carbonate (Calcichew-500), given orally as 2 chewable tablets per day, one midmorning and one late afternoon, for 15.5 months. The calcium regimen was tested in a 2x2 factorial study with or without a supervised exercise program.

Calcium supplementation improved bone mineral status at several skeletal sites, with larger effects in more compliant participants. Among good compliers, effects were seen for whole body BMC 0.8 ± 0.3%, lumbar spine 1.9 ± 0.5%, ultradistal radius 1.3 ± 0.6%, total hip 2.7 ± 0.6%, femoral neck 2.2 ± 0.7%, and trochanter 4.8 ± 0.9%. Exercise had no significant intention-to-treat effect on size-adjusted BMC overall, but participants attending >50% of sessions showed increases at total hip 1.4 ± 0.7% and trochanter 2.6 ± 1.2%. No interaction between calcium and exercise was detected, suggesting additive rather than synergistic effects.

Per-arm sample sizes were modest, especially for subgroup and compliance analyses. Exercise adherence was limited, with only a minority attending more than half of sessions, which weakens interpretation of the exercise findings. The trial did not assess fracture outcomes or whether the bone benefits persisted after supplementation ended.