Writing in The Journal of Clinical Endocrinology & Metabolism, lead author Thomas Carpenter and his co-workers looked at the effect of a daily supplement of 300 mg magnesium and found significant increases in the bone mineral content, particularly in the hip bone.
While several studies have reported positive effects of magnesium on bone mineral density in adults, Carpenter said that no interventional study has focussed on adolescents, a key age group in bone formation that may have long-term implications, particularly in osteoporosis development.
Osteoporosis is characterized by low bone mass, which leads to an increase risk of fractures, especially the hips, spine and wrists. An estimated 75 million people suffer from osteoporosis in Europe, the USA and Japan.
Women are four times more likely to develop osteoporosis than men.
Potential reduction of osteoporosis has traditionally been a two-pronged approach by either attempting to boost bone density in high-risk post-menopausal women by improved diet or supplements, or by maximising the build up of bone during the highly important pubescent years.
About 35 per cent of a mature adult's peak bone mass is built-up during puberty.
The prospective, placebo-controlled, randomised, one-year double-blind trial involved healthy Caucasian girls (age range 8-14), with participants recruited from the 120 volunteers with daily dietary magnesium intakes lower than 220 milligrams.
The girls were randomly assigned to receive either two doses of elemental magnesium (as magnesium oxide) to give a total daily dose of 300 mg, or placebo for one year. Bone mineral content (BMC) changes in specified sites (total hip, femoral neck, Ward's area, and lumbar spine) were measured.
The researchers report: "Significantly increased accrual in integrated hip BMC occurred in the Mg-supplemented vs. placebo group. Trends for a positive Mg effect were evident in the pre- and early puberty and in mid-late puberty."
Carpenter reports that, on average, the girls consumed at least 73 per cent of the capsules.
"Oral Mg oxide capsules are safe and well tolerated. A positive effect of Mg supplementation on integrated hip BMC was evident in this small cohort," concluded the researchers.
Dietary sources of magnesium include green, leafy vegetables, meats, starches, grains and nuts, and milk. Earlier dietary surveys show that a large portion of adults do not meet the RDA for magnesium (320 mg per day for women and 420 mg per day for men).
Source: The Journal of Clinical Endocrinology & Metabolism Volume 91, Number 12, Pages 4866-4872 "A Randomized Controlled Study of Effects of Dietary Magnesium Oxide Supplementation on Bone Mineral Content in Healthy Girls" Authors: T.O. Carpenter, M.C. DeLucia, J.H. Zhang, G. Bejnerowicz, L. Tartamella, J. Dziura, K. Falk Petersen, D. Befroy and D. Cohen