Calcium supplementation increases stature and bone mineral mass of 16- to 18-year-old boys.

Randomized, placebo-controlled trial in healthy male sixth-form students aged 16 to 18 years from Cambridge, UK. Randomization was stratified by customary physical activity level and college, and the active calcium group included 73 participants with 70 in placebo in the final dataset.

Daily oral calcium supplementation with orange-flavored chewable calcium carbonate tablets providing 1000 mg elemental calcium per day, given as two Calcichew-500 tablets. Participants were asked to take one tablet mid-morning and one in the evening, away from meals, for about 12 to 13 months versus placebo.

Calcium supplementation produced a clear positive effect on skeletal growth and bone mineral accretion in late-adolescent boys. Compared with placebo, the supplement group had greater height gain by 0.4%, P = 0.0004, about 7 mm, along with higher lean mass by 1.3% and whole-body BMC by 1.3% (both P = 0.02). Bone gains were also seen at key sites, including lumbar spine BMC 2.5% (P = 0.004), hip total BMC 2.3% (P = 0.01), femoral neck BMC 2.4% (P = 0.02), and intertrochanter BMC 2.7% (P = 0.01). There were no significant effects on body weight, fat mass, or fat fraction, and no side effects were reported.

Single-center study in healthy, predominantly white adolescent boys, which limits generalizability. Follow-up was relatively short and the intervention effect on some bone outcomes was reduced after adjustment for skeletal size, suggesting part of the benefit was mediated by growth rather than direct mineralization alone. Compliance was variable, and subgroup interactions by physical activity and testosterone complicate interpretation.