Two weeks ago reports warned of vitamin C's previously unknown potential to do serious harm in large doses. Now in a letter published in today's issue of the New England Journal of Medicine, researchers decribe the deleterious effects of overdoing it with other vitamins. Michael Holick, director of the Bone Health Care Center at Boston University Medical Center, and his colleagues review the case of a 42-year-old man hospitalized for symptoms of hypercalcemia, or excessive levels of calcium in the blood. The condition most commonly results from a malignancy or parathyroid disease but, in this instance, the patient had accidentally taken too much vitamin D.

The man had used an over-the-counter supplement containing vitamin D for two years before his hospitalization, at which point his serum level was more than 10 times the healthy upper limit. When the man stopped taking the supplements, his vitamin D levels slowlyover the course of 30 monthsreturned to normal. When doctors examined the supplements the patient took, as well as others they purchased separately, they were surprised to find that these pills contained 26 to 430 times the amount of vitamin D claimed on the label. "That's 78 to 1,302 times the recommended safe upper limit of 2000 IU [International Units]," Holick says. "Our intention is not to frighten people who take supplements but to make them aware that these products are not FDA approved and thus are not as stringently regulated as products that are."