More vitamin C means fewer cataracts.

Women who took vitamin C supplements for at least 10 years proved only 23 percent as likely to develop cataracts as women who received the vitamin only in their diet, a new study finds.

Allen Taylor of the U.S. Department of Agriculture Human Nutrition Research Center on Aging at Tufts University in Boston has been probing the relationship between cataracts and antioxidant vitamins, such as vitamin C, for more than a decade. Initially working with eye tissue in the laboratory, he and his colleagues have shown that vitamin C can slow the chemical reactions that make certain lens proteins clump together, causing cataracts. The group then demonstrated that giving animals the vitamin retarded cataract development.

Now, in the October American Journal of Clinical Nutrition, the scientists describe evidence that the human eye derives similar benefits from vitamin C.

The new study, headed by USDA epidemiologist Paul F. Jacques, recruited local women from the Nurses' Health Study. This Harvard University project has been charting diet and disease in more than 120,000 women since 1972.

The researchers identified some 56- to 71-year-olds who in the early 1980s had taken vitamin C supplements and others who had not. Of the women, 165 supplement users took eye tests, as did 136 women with no added vitamin C.

Though none of the women had been diagnosed with cataracts, 188 showed at least early signs of the disease. Sixty percent of these early cataracts appeared in women who had never taken supplements; moreover, the risk of cataracts decreased as the duration of supplementation increased. The mean dietary intake of vitamin C for women not taking supplements was 130 milligrams per day-about twice the recommended amount but less than one-third the average of women taking supplements.

A few other studies have found signs that antioxidant supplements inhibit cataract formation, Jacques notes, but they suffered from potential bias because the women knew whether they had cataracts before answering questions about diet. Previous studies also tended to collect dietary data just once, rather than repeatedly over a decade.

The new study suggests that the protective effect of long-term vitamin C supplements "could be quite strong," notes Julie A. Mares-Perlman of the University of Wisconsin-Madison Medical School in an accompanying editorial. However, she adds, with only about 25 women in the long-term supplement group, there were too few to establish the magnitude of benefits.

A larger, planned follow-up of randomly selected participants in the nurses' study should resolve this issue, Jacques says, as well as whether other antioxidants--such as vitamin E and carotenoids--offer similar protection.