According to the paper, there was an approximate 2 percent increase in whole-body BMD for every 100 milligram per day increase in magnesium.

"Higher magnesium intake through dietary change or supplementation may provide an additional strategy for the prevention of osteoporosis," researchers conclude.

Osteoporotic fractures are a significant health problem in aging adults, Dr. Kathryn M. Ryder, of the University of Tennessee, Memphis, and colleagues note in their report. Given the high prevalence of low BMD and fracture, small improvements in BMD may have a large public health effect,

Magnesium is a "lesser-studied" component of bone that may play a role in calcium metabolism and bone strength, they add.

Ryder's group examined magnesium intake from supplemental and dietary sources in relation to BMD in a total of 2038 black and white subjects between the ages of 70 and 79 years enrolled in the cross-sectional Health, Aging, and Body Composition Study.

They used a semiquantitative food frequency questionnaire to assess dietary intake of magnesium and standard tests to measure BMD.

Less than 26 percent of the study sample met the RDA for magnesium, the investigators report.

White and black women reported a similar intake of food magnesium, but because of more frequent magnesium-containing supplement use, white women had a higher total mean intake. Compared to black men, white men reported higher food magnesium, use of magnesium-containing supplements, and total magnesium intake.

After multivariate adjustment, magnesium intake was positively associated with BMD in white, but not black, men and women. The lack of an association in black men and women may be due to differences in calcium regulation or in nutrient reporting, the researchers suggest.

SOURCE: Journal of the American Geriatrics Society, November 2005.