March 19, 1998
Diet and Exercise
Osteoporosis
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Articles from The New York Times archives have not been edited to reflect the most recent research. Consult your health professional for the most up-to-date information. Osteoporosis Linked to Vitamin D Deficiency
By JANE E. BRODY
A new study strongly suggests that widespread deficiencies of vitamin D may play a big role in causing the bone-wasting disease osteoporosis among older Americans.
The researchers attributed vitamin D deficiencies to two factors of growing importance: insufficient dietary intake and inadequate exposure to sunlight, which stimulates production of vitamin D in the skin.
The study findings, being published today in The New England Journal of Medicine, suggest not only that millions of American adults lack enough vitamin D in their blood to protect their bones but also that newly upgraded recommendations for vitamin D intake may be inadequate to prevent osteoporosis in many older people. Although calcium is the main nutrient of concern for preventing osteoporosis, vitamin D also plays an important role.
Deficient levels of vitamin D were found in the blood 37 percent of those who reported consuming the newly recommended amounts of 400 international units (I.U.) a day for people 51 to 70 years old and 600 international units for those over 70. The previous recommendation for all adults had been 200 international units.
The study was conducted by Dr. Melissa K. Thomas and colleagues at Massachusetts General Hospital among 290 hospitalized patients, who might be expected to have lower--than average levels of vitamin D in their blood. And indeed more than half of them did. Using a conservative measure of deficiency, Dr. Thomas said 57 percent of the patients were deficient, including 22 percent who were severely deficient in this essential nutrient.
Asked whether the findings in hospital patients could be applied to the general population, Dr. Thomas said that although the percentage of people with vitamin D deficiency might be somewhat lower in healthy people, the problem was still likely to be widespread. Dr. Thomas based this judgment on a separate analysis of vitamin D levels among 44 patients who were younger and healthier and had none of the usual risk factors that might cause a vitamin D deficiency. Yet she found that 42 percent of them were deficient.
The results of this and other studies suggest that at least for adults living at northern latitudes where essentially no vitamin D is made in the skin all winter, a dietary supplement of 800 international units a day may be needed to stave off a chronic deficiency. In an editorial accompanying the new report, Dr. Robert D. Utiger, a specialist in endocrinology, pointed out that low vitamin D levels had been found in 46 percent of those who reported taking multivitamins, most of which contain 400 international units of vitamin D.
Vitamin D aids in the absorption of dietary calcium, but its most important role is in maintaining normal blood levels of calcium. In the patients labeled deficient, levels of vitamin D in the blood were low enough to cause calcium to be removed from their bones to supply the blood. Adults deficient in vitamin D cannot properly mineralize their bones, which gradually come to resemble a rubbery framework without cement.
A recent study of 3,270 healthy elderly French women showed that a dietary supplement of calcium plus 800 international units of vitamin D a day decreased the risk of hip fractures by 43 percent in just two years.
Dr. Michael Horlick, chief of endocrinology at Boston University Medical Center, said there was now enough evidence to conclude that "vitamin D deficiency is an unrecognized epidemic in our middle-aged and older population -- both in patients and in healthy people throughout the year." For example, in a recent study he did among 160 Bostonians 49 through 83 years old who visited the hospital clinics, 40 percent were deficient in vitamin D.
Dr. Horlick's studies have shown that the American diet is an unreliable and generally poor source of vitamin D. The only major dietary source is milk that has been fortified with vitamin D, supposedly at a minimum level of 400 international units in each quart. But he said he found that "no more than 20 percent of milk samples throughout the nation contained at least 320 I.U. per quart and 15 percent of skim milk samples had no detectable vitamin D at all, even though the label said they were fortified with vitamin D."
"About 90 percent of the vitamin D in most people comes from casual exposure to sunlight," Dr. Horlick said. "But the concern about cancer risk has limited people's exposure to sunlight."
Speaking of a sun protection factor, he added, "If you religiously apply sunscreen with an S.P.F. of 8 to your exposed skin, you will make no vitamin D."
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