Adolescents in many developing countries do not consume sufficient calcium in their diet to protect bones against the common condition osteoporosis.
In the UK for example, the latest National Diet and Nutrition Survey revealed that 19 per cent of girls and 9 per cent of boys aged between 15-18 years are not getting enough calcium from their diets, increasing their risk of failing to achieve their peak bone mass (at age 20-25) and consequently, of developing osteoporosis later in life.
However the effects of short-term calcium supplementation on peak bone mass in adolescent girls have not been completely defined, according to a team from the Technion-Israel Institute of Technology and the Rambam medical center.
In a previous double-blind, placebo-controlled, calcium-supplementation study, the researchers demonstrated that girls with low calcium status that took 1000 mg of calcium carbonate each day for a year increased bone mineral acquisition.
In a new follow-up study, completed 3.5 years after the end of the supplementation period, they found that those who had taken supplements tended to have a greater accretion of total-body bone mineral density than the control group.
They write in this month's American Journal of Clinical Nutrition (vol 81, no 1, pp168-174) that the calcium group (17 subjects) had a compliance rate of at least 75 per cent during the intervention study.
In another study in the same journal however (pp175-188), US researchers report that calcium-supplementation effects vary over time.
They carried out a randomized clinical trial on 354 females in puberty with a mean dietary calcium intake of 830 mg per day. The calcium-supplemented group received an additional 670 mg per day.
All of the primary outcomes - proximal radius bone mineral density (BMD), total-body BMD, and metacarpal cortical indexes - were significantly larger in the supplemented group than in the placebo group at the year four endpoint.
However, at the year seven endpoint, this effect vanished for total body BMD and distal radius BMD, write the researchers.
Longitudinal models for total body BMD and proximal radius BMD showed a highly significant effect of supplementation during the pubertal growth spurt and a diminishing effect thereafter.
"These results may be important for both primary prevention of osteoporosis and prevention of bone fragility fractures during growth," they conclude.