Magnesium deficiency may contribute to osteoporosis rise.
Increasing magnesium intake could increase bone density in the elderly and reduce the risk of osteoporosis, suggests a large American study.
"Higher Mg intake through diet and supplements was positively associated with total-body [bone mineral density] BMD in older white men and women. For every 100 mg per day increase in Mg, there was an approximate 2 per cent increase in whole-body BMD," said Kathryn Ryder and colleagues.
Osteoporosis is characterized by low bone mass, which leads to an increase risk of fractures, especially the hips, spine and wrists. An estimated 10 million people suffer from osteoporosis in the US alone, while another 34m are believed to have low bone mass, which puts them at risk of developing the disease.
Women are four times more likely to develop osteoporosis than men.
More than 2,000 volunteers aged 70 to 79 took part in the cross-sectional American study by completing a food-frequency questionnaire. All supplements and dietary intakes of magnesium were calculated from ingredients databases.
The authors did not identify the exact role of magnesium, but suggested it may be via calciotropic hormones, by acting as a buffer against acidic Western diets, or by substituting for calcium in the bones.
Magnesium intake was positively associated with BMD in white, but not black, men and women. These observations could be due to racial difference in calcium regulation or nutrient responses.
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).
Responding to this study, a spokesperson for the UK-based charity, the National Osteoporosis Society, said: "Although there have been previous studies into the effect of magnesium on bone density, it is always encouraging to learn of studies which help build upon our knowledge of bone health."
"Some research has suggested that a low magnesium level may be a risk factor for osteoporosis although magnesium deficiency is, in fact, very rare in humans. As yet there is no evidence that magnesium supplementation reduces fracture risk," she said.
For healthy bones the Society recommends a mixed, well-balanced calcium-rich diet and regular weight-bearing exercise.
The study was published in the Journal of the American Geriatric Society (November, Vol 53, No 11, pp 1875-1880).
Related Article: Getting Enough?
Last year, the National Academy of Sciences announced new recommended intakes for magnesium.
- Women need 310 mg a day (ages 19 through 30) or 320 mg (over 30)
- Men need 400 mg (19 through 30) or 420 mg (over 30)
How much magnesium are you getting? And is it enough to keep you from running short?
"Unfortunately, there isn't a reliable test of magnesium deficiency that's widely available," says the University of Southern California's Robert Rude. "About all a primary care physician can do is measure the level of magnesium in the blood. But that doesn't tell you if the level of magnesium is adequate within the cells, which is where it's critically important."
"I think that magnesium should be obtained from the diet, if possible," says Jerry Nadler of the City of Hope Medical Center in Duarte, California. "That's because many magnesium-rich foods are the healthier foods to eat." But if someone can't get enough from food (see "Magnesium Counts," p. II), "then taking a magnesium supplement clearly is better than nothing."
Multivitamin and mineral supplements seldom contain a day's recommended dose of magnesium, simply because the 300 or 400 mg necessary won't fit into a pill small enough for most people to swallow. So if you want more than 25 percent or so of a day's supply from a supplement, you'll probably need to buy it separately.
Don't worry about how the magnesium is bundled-whether it comes in an oxide, chloride, or any other form. "There's no convincing evidence that one is better-absorbed than another," says Connie Weaver of Purdue University. And don't be afraid to get your calcium and your magnesium in a single supplement. "Calcium doesn't interfere with magnesium absorption, as some people believe," says Weaver.
But not all magnesium supplements are equal. Dolomite (a naturally occurring calcium-magnesium combination) is more likely to contain lead than other kinds of magnesium.
Can you get too much magnesium? "Taking too much from magnesium-confining antacids or drugs causes diarrhea," says magnesium expert Mildred Seelig. "So most people find out quickly when they've exceeded a safe dose."
No cases of magnesium toxicity from food have ever been reported, says the National Academy of Sciences. As for supplements, the NAS recommends a ceiling of 350 mg a day as a Tolerable Upper Intake Level (UL).
Related Article: The Bottom Line
- The average American gets too little magnesium from food. The richest sources are legumes, nuts, whole grains and wholegrain breads and cereals, and some vegetables.
- Too little magnesium in the diet could increase the risk of diabetes, high blood pressure, heart disease, and stroke, but the evidence isn't conclusive.
- With the possible exception of treating migraines, there's no good evidence that getting more than the recommended levels of magnesium (see "Getting Enough?") - from food or supplements - provides any additional benefits.
COPYRIGHT 1998 Center for Science in the Public Interest
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