Vitamins C and E may prevent cataracts.

Vitamins C and E May Prevent Cataracts

A Canadian epidemiologic study suggests vitamin C and vitamin E supplements help prevent cataracts in humans. The new findings, which seem to coroborate vitamin C-related results from a similar U.S. study, represent the first time researchers have shown a relationship between vitamin E intake and cataract prevention in humans, says study coauthor James McD. Robertson at the University of Western Ontario in London.

If confirmed, the work could lead to a "tremendous" public health benefit, says Allen Taylor of the USDA Human Nutrition Research Center on Aging in Medford, Mass. "If you could delay cataract formation by just 10 years, you would eliminate the need for half of the cataract extractions," he says. Cataracts, which can lead to blindness, afflict 20 percent of people between the ages of 60 and 75 in the United States, prompting half a million surgical procedures each year, Robertson says.

Animal studies have suggested a biological basis for the epidemiologic findings. Last year, Robertson's colleague John R. Trevithick and his team showed that diabetic -- and therefore cataractprone -- rats given high dietary levels of vitamin E had less lens-protein leakage than did controls, indicating reduced cataract formation in the treated rats. And experiments with guinea pigs have demonstrated that vitamin C boosts the amount of ascorbic acid in the eye, helping to stop cataract formation (SN: 6/28/86, p.410). Now that epidemiologic observations suggest these results may apply to humans, a clinical intervention trial appears warranted, Robertson says.

Robertson, Trevithick and Allan P. Donner compared the self-reported supplemental vitamin intake, general health, education and other demographic characteristics of 175 cataract patients over the age of 55 living in southwestern Ontario with those of 175 age- and sex-matched cataract-free adults. The scientists found that the only significant difference between the two groups, other than the presence of cataracts, was that the cataract-free individuals had taken at least 400 international units (one regular capsule) of vitamin E and/or a minimum of 300 milligrams of vitamin C per day over the last five years. They assumed the patients and controls ate similar diets because of similar backgrounds.

People who took only vitamin E supplements had about 50 percent less cataract risk than those who took no vitamins. Those taking vitamin C alone showed a 70 percent risk reduction, the researchers say. They hesitate to draw conclusions about the advantage of taking both vitamins, because very few of the study's subjects did so. Their report is scheduled to appear this fall in the ANNALS OF THE NEW YORK ACADEMY OF SCIENCES.

Cataracts form when proteins oxidize in the lends of the eye, aggregating into opaque clumps. The lens harbors enzymes that counter the process, but these also oxidize as the eye ages. Vitamins E and C are antioxidants, and so prevent lens proteins from clumping.

Recent research in Japan has demonstrated that the shorter-lived, water-soluble vitamin C works to rejuvenate the eye's supply of the fat-soluble vitamin E, which is oxidized -- and so becomes inactive -- when it neutralizes the free radicals that might otherwise cause cataracts, Trevithick says. Sunlight, X-rays, diabetes and steroids all may contribute to the risk of cataracts, Robertson told SCIENCE NEWS.