studies suggest that high intake of
, and carotenoids (
—are associated with a reduced incidence of cataracts.
However, this by itself does not prove that the use of antioxidant supplements can prevent cataracts. Only
studies can do that. (For information on why the double-blind design is so important, see
Why Does This Database Rely on Double-blind Studies?
) Unfortunately, the results of several large studies of this type were not encouraging.
In an enormous, double-blind, placebo-controlled trail involving almost 40,000 female healthcare professionals, use of natural
at a dose of 600 mg every other day over a 10-year period failed to have any effect on cataract development.
In another large, 8-year trial, 11,545 physicians aged 50 years and older were randomized to four different treatment groups: vitamin E (400 units) every other day plus vitamin C (500 mg) daily, vitamin E every other day plus placebo daily, vitamin C daily plus placebo, or placebo only.
Neither vitamins E or C had any significant effect on preventing cataracts.
And, in a similar trial, 4,629 older people received either placebo or an antioxidant supplement containing 500 mg of vitamin C, 400 IU of vitamin E, and 15 mg of beta-carotene. The results over more than 6 years showed no effect on the risk of development of cataracts, nor the rate at which existing cataracts progressed to greater severity.
A 5-year double-blind, placebo-controlled study of 798 people in Southern India failed to find benefit with supplemental antioxidants, despite the fact that dietary antioxidant deficiency was common among the people studied.
In addition, a previous double-blind, placebo-controlled study examining the use of beta-carotene or vitamin E alone in male smokers failed to find the supplements effective.
On a more positive note, though, one large study found that beta-carotene supplements helped prevent cataracts in the subgroup of study participants who smoked.
However, no benefits were seen in the group as a whole. In any case, people who smoke are generally not advised to take extra beta-carotene. (For the reasons behind this concern, see the
In another long-term study involving over 1,000 older adults, multivitamin and minerals supplements led to a significant decrease in the development of cataracts compared to placebo over a 9-year period. However, these favorable results were tempered by an inexplicable increase in the number of a subtype of cataracts (posterior subcapsular) occurring among those taking the multivitamin/mineral supplements.
A very small, 2-year study found some evidence that
may improve visual function in people who already have cataracts.