All age groups lack vitamin D in blood.

While calcium is a hot seller these days, its partner in physiology, vitamin D, has been largely neglected. The body needs vitamin D to absorb calcium, but since people can get the vitamin from sunlight and various foods fortified with it, most of them assume they get enough.

Unfortunately, they're often wrong -- and the consequences can affect them right down to the bone.

Previous research on vitamin D has focused primarily on elderly people, who face a serious risk from a deficiency. Now, a Massachusetts team reports that younger people often lack sufficient amounts as well. This deficiency has been linked to osteoporosis, or brittle bone disease, because the body extracts calcium from bone when it doesn't have enough vitamin D on hand to absorb adequate calcium from food.

Researchers tested blood samples taken from a total of 290 consecutive patients arriving at Massachusetts General Hospital during March and September 1994. Fifty-seven percent had insufficient vitamin D, report Joel S. Finkelstein of Harvard Medical School and Massachusetts General Hospital in Boston and his colleagues in the March 19 New England Journal of Medicine.

Most housebound people and people over age 65 were found deficient, a result that mirrors past studies. Elderly people tend to lack vitamin D in their diets and get outside less often than younger people.

Surprisingly, 42 percent of the 77 healthy, nonelderly people tested also showed a deficiency. These people, whose age averaged 44, had come to the hospital with complaints, such as chest pains, that turned out not to stem from medical problems.

Since thinning bone isn't apparent until a fracture occurs, these younger people wouldn't notice any effects of vitamin D deficiency, says Michael Parfitt of the University of Arkansas for Medical Sciences in Little Rock.

The researchers took blood samples at two times of year in order to explore the effect of sunlight. In March, nearly two-thirds of the people tested were deficient in vitamin D. In September, half lacked a proper amount.

The Institute of Medicine's Food and Nutrition Board recommends 200 International Units (IUs) of vitamin D daily for people age 19 to 50 and more for older folks. Multivitamin pills typically contain at least 400 IUs, yet nearly half of the 54 people in the study who reported taking multivitamins daily were deficient in vitamin D, as determined by measurements of 25-hydroxyvitamin D, a hormone derived from the vitamin. "We can't tell you why so many people are deficient," says Finkelstein.

The study raises the possibility that recommended intakes of vitamin D are too low, even though they were raised just last year, says endocrinologist Robert D. Utiger in an editorial accompanying the report. Milk infant formula, and some margarines and cereals are fortified with vitamin D, but the amounts are inconsistent. "Fortification of other foods should be considered," Utiger suggests.

Whether people should be screened for vitamin D deficiency or advised to take more vitamin D is still an open question, says Harvard endocrinologist and study coauthor Melissa K. Thomas.

The researchers used a conservative measure of vitamin D deficiency, says Bess Dawson-Hughes, an endocrinologist at the U.S. Department of Agriculture Nutrition Center at Tufts University in Boston. They chose as a minimum safe concentration 15 nanograms of 25-hydroxyvitamin D per milliliter of blood serum. Even people with 25 to 30 nanograms per milliliter could be mildly deficient, Dawson-Hughes says. "The magnitude of the problem is substantial."