VITAMINS AND CATARACTS:
DO THEY OR DON’T THEY PREVENT CATARACTS

(January 2003)

There are three types of cataracts that are located in different parts of the lens of the eye. Those in the outer part of the lens are called posterior subcapsular; inside those are the cortical cataracts, and those most central are called nuclear. Of the three, posterior subcapsular occurs the least frequently. Cortical and posterior subcapsular cataracts in relation to diet and vitamin supplements are analyzed in a report in the March 2002 issue of the American Journal of Clinical Nutrition. The investigators studied 492 nurses, ages 53 to 73 years, who had been followed for at least seventeen years. Food intake and vitamin use were determined multiple times during the study period.

A total of 86 posterior subcapsular and 246 cortical cataracts were detected. The investigators found no relationship between any antioxidants or vitamins and likelihood of developing cataracts when they analyzed all the cataracts together. Then, they did a lot of sub-analyses and found that vitamin C, if taken in dosages of 360 or more milligrams a day, far over the recommended 70 milligrams a day, reduced risk of cortical cataracts by almost 60 percent in women under age 60.. However, among women taking 240 to 360 milligrams, the risk actually appeared increased (more than doubled). This finding was given less weight because, when the women were divided into five groups (quintiles) according to vitamin C intake, the trend of increasing dosages of vitamin C reducing cataract risk was statistically significant (despite the increased risk in the second highest dosage quintile). Women under age 60 taking vitamin C containing supplements for at least five years showed a 67 percent reduction in cortical cataracts, but women over age 60 taking vitamin C supplements for five to nine years had a doubled risk of cortical cataracts..

The other finding was that for those who never smoked cigarettes (but not for anyone who ever smoked even a little bit), an increase in total carotenoid intake (alpha and beta carotenes, lycopenes, lutein/zeaxanthin) reduced posterior subcapsular cataract risk by 66 percent. The reduction in risk of posterior subcapsular cataracts with increasing folic acid intake was even greater (more than 70 percent).

The authors concluded "our results support a role for vitamin C in diminishing the risk of cortical cataracts in women less than age 60 years and for carotenoids in diminishing the risk of posterior subcapsular cataracts in women who have never smoked.

Commentary: This remains a muddled area. It makes sense that antioxidants could reduce risk of cataracts because the lens of the eye is exposed to oxidant stress. But, there are huge inconsistencies among the various studies. Some show no benefits at all from antioxidants and among the studies that do show benefit, there is little consistency about which antioxidants are providing the benefit - vitamin C, vitamin E, folic acid, beta carotene, other carotenoids (lutein, xeaxanthin, alpha carotenoids) all have been found to protect in some studies and do nothing in other studies. (For example, see Archives for a solid multicenter study recently reviewed titled "Antioxidants, zinc, and prevention of age-related blindness").

In this study, there are puzzling inconsistencies. Why did vitamin C reduce risk only in women under 60 years of age? Why are there discrepancies such as the increased risk for women under age 60 taking the second highest dosage of vitamin C? Why in women over age 60 using vitamin C supplements for five to nine years should there be an increased risk?

It also appears the authors analyzed cataracts by eyes, not persons; so, if a woman had a cataract in both eyes or two cataracts in one eye, they were considered separately. That could markedly bias the results.

Cataracts are a huge problem. Almost one-half of persons over 75 years of age will lose some vision because of cataracts; and cataract surgery is the single greatest surgical cost in Medicare.

But,

At present, there is still no dietary or dietary supplement prescription that will predictably reduce the likelihood of developing any type of cataract. It still makes sense to have a good amount of antioxidants in your diet and, if there is any question about getting enough folic acid in the diet, a folic acid supplement (400 or 800 micrograms) is strongly recommended.

Taylor, A., et al. Long-term intake of vitamins and carotenoids and odds of early age-related subcapsular lense opacities. American Journal of Clinical Nutrition. Vol 75 (March) Pgs 540-549. 2002.