Vitamin C and Cataract Risk in Women

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Vitamin C is an antioxidant that plays many important roles in the body, including infection control, the preservation of tissue health, and the production of hormones and brain chemicals. Years ago, Nobel laureate Linus Pauling advocated megadoses--1,000-2,000 mg per day--to fend off colds and prevent cancer. Studies have found no benefit from such massive doses, but a different line of research suggests that just a little extra might be a good thing for women's eyes.

CATARACT AND VITAMIN C
Cataract is a clouding of the eye's lens that causes progressive loss of vision. It affects more than half of all Americans over age 65. Several studies, including the Nurses' Health Study, have associated vitamin C with reduced risk for nuclear cataract, the most common type and the one associated with aging. We know less about how antioxidants, and vitamin C in particular, affect the development of cortical cataract and posterior subscapsular cataract (PSC), which often develop in diabetics. Now, however, research by the Nutrition and Vision Project (NVP), a cooperative effort of Harvard and Tufts University scientists, has found that women who consume higher-than-recommended doses of vitamin C may lower their risk for more than one type of cataract.

THE STUDY
The NVP used data from a group of 492 women, ages 53-73, participating in the Nurses' Health Study. NVP scientists investigated each woman's nutrient intake and cataract incidence, analyzing food and supplement information over a 13-15 year period prior to a detailed eye examination. Results appeared in the March 2002 American Journal of Clinical Nutrition.

Researchers found early cataracts--before visual symptoms--in more than 50% of the eyes examined. But women under age 60 with a daily vitamin C intake of 352 mg or more were 57% less likely to develop cortical cataracts than those whose intake was less than 140 mg/day. And women under age 60 who had taken vitamin C supplements for at least 10 years had a 60% lower risk for such cataracts. Vitamin C intake itself did not seem to affect the risk for PSC. Only nonsmokers with high intakes of other antioxidants had fewer of them, which suggests a possible role for vitamin C because smoking reduces blood levels of vitamin C.

WHAT IT MEANS
Any protective effect of vitamin C probably occurs well above the Recommended Dietary Allowance (RDA) of 75 mg/day for women, about the amount in an orange. (The RDA for women who smoke is 110 mg/day.) NVP subjects who consumed 352 mg of vitamin C or more per day usually took supplements.

Other studies on this subject have produced mixed results, so scientists aren't ready to recommend specific nutrient levels for cataract prevention. But while we await further evidence, boosting our vitamin C intake from both food and supplements to around 500 mg/day is probably a good idea. Discuss it with your clinician, especially if you have an increased risk for kidney stones.

Where Cataracts Form
DIAGRAM: Nuclear cataract occurs at the lens center (nucleus). Cortical cataract forms in the intermediate cells (cortex) of the lens. And posterior subcapsular cataract (PSC) starts under the outer membrane (capsule) at the back of the lens.

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