Antioxidant or Multivitamin Supplements to Prevent Cataracts

Cataracts are a direct result of oxidative stress, free radical damage to the normally transparent crystallin proteins that make up your lenses. The oxidative stress can come from hyperbaric oxygen therapy, artificial UV rays of tanning beds, the natural UV rays of the sun, or other forms of high energy radiation. For example, all 21 studies of health care workers exposed to x-rays, like those who do angiograms, found higher rates of cataracts, 15 of which significantly so.

If cataracts are caused by oxidation, how about eating more antioxidants? The body concentrates vitamin C in the lens at levels 50-fold higher than the blood to defend against oxidative attack. Experiments in which samples of eye fluid are taken during cataract surgery after vitamin C supplementation confirm that changing what goes into our mouth can change what ends up in our eyes, but does that translate into lower risk?

Those eating diets with a higher total antioxidant content due tend to have lower risk of age-related cataract. The same could be said for the intake of some individual antioxidants—vitamin C, beta carotene, and lutein/zeaxanthin—but not others (vitamin A, vitamin E, or alpha carotene). For vitamin C, both intake and blood levels correlated with lower cataract risk. Those getting about two oranges worth a day appeared to have approximately 40 percent lower risk. Researchers concluded that dietary vitamin C intake “should be advocated for the primary prevention of cataract,” mirroring similar advice from a meta-analysis on dietary lutein/zeaxanthin and cataract risk: “ophthalmologists should counsel individuals to increase consumption of lutein-rich foods, such as dark-green leafy vegetables.” Why not just recommend antioxidant supplements instead?

While vitamin C intake from foods is associated with lower cataract risk, vitamin C intake from supplements may not be. A red flag was raised by the Swedish Mammography Cohort study that followed about 25,000 middle-aged and older women for years. Those who reported taking vitamin C supplements were 25 percent more likely to end up getting cataract surgery. That number rose to 38 percent in women 65 and older, and 46 percent for women taking vitamin C for more than 10 years. A similar prospective study on men found the same thing. To see if the apparent increased risk is due to the supplements themselves, or just something about the type of people who would choose to take such supplements, you’ve got to do an interventional trial. By randomizing people to take something whether they would choose to or not separates the effect of the actual substance with any factors attached to the motivation.

More than 10,000 physicians were randomized to take vitamin C, vitamin E, or neither (placebos) for eight years. No effect was found for either. A combination of vitamins C, E, and beta carotene also failed to affect the rate of cataract formation. Why did antioxidant-rich foods appear to help but antioxidant-rich supplements fail? Maybe the supplement studies didn’t last long enough? (It may take decades for cataracts to manifest). Or, maybe the doses were too high? Or, maybe because there are other protective components of antioxidant-rich foods, or the multiplicity of compounds in whole foods working together.

Or, maybe there’s a threshold effect such that supplementation would only work in the context of dietary deficiency? For example, consider the case of the greens nutrients lutein and zeaxanthin, the only carotenoids present in the human lens. So, perhaps it’s no surprise that beta carotene failed to help. Lutein and zeaxanthin supplementation also failed but only among those getting enough in their diet. Those with the lowest baseline intake did appear to benefit from supplementation. Those with an inadequate baseline intake of greens would also presumably benefit from just eating more greens.

Taking supplements just as an “insurance policy” is a common sentiment heard in the context of multivitamin and multimineral supplements. In the Age-Related Eye Disease Study, study participants were offered a multivitamin/mineral supplement. The two-thirds that decided to take it did tend to get fewer cataracts but again, maybe it’s just something about the people that would make that choice. An interventional trial in a nutritionally-deprived population in China found that those randomized to a multivitamin/mineral supplement experienced a 36 percent drop in the risk of developing cataracts compared to the placebo group. To see if this might translate into better nourished populations, randomized controlled trials were performed in the U.S. and Italy.

Male physicians in the U.S. randomized to a multivitamin/mineral supplement for about a decade were 9 percent less likely to develop cataracts than those randomized to placebo. In Italy, men and women randomized to the same multivitamin/mineral supplement (Centrum) for about a decade had a 34 percent lower risk of developing or worsening center-of-the-lens (nuclear) cataracts, but 100 percent greater risk (doubled risk) for developing or worsening back-of-the-lens (posterior subcapsular) cataracts. Though posterior cataracts are faster growing, nuclear cataracts are so much more common that there were fewer cataract problems overall in the supplement compared to placebo group, but the opposite effects of the multivitamin on the development of the two different types of cataracts, concluded the researchers, “prevent us from making recommendations….”