Women who take high-dose vitamin C supplements have a higher risk of developing age-related cataracts.

To look into the association of vitamin C supplements and incidence of age-related cataract, researchers examined 24,593 Swedish women, aged between 50 and 80 years. Overall, 59 percent of the 49 to 83 years old otherwise healthy women said they used a dietary supplement. Of these 5 percent only took vitamin C supplements and 9 percent took only multivitamins that contained about 60 milligrams of vitamin C. Of the 1,225 women who took only vitamin C supplements, 143 (nearly 13 percent) had cataracts removed during the study period.

By comparison, cataracts were removed in 878 of 9,974 women who did not use any supplements (roughly 9 percent) and in 252 of 2,259 multivitamin-only users (about 11 percent). Those who reported regular or occasional vitamin C supplementation of about 1000 milligrams per serving were about 25 percent more likely than those who did not take supplements to have age-related cataracts removed. Women who took extra vitamin C for 10 years or longer; or in combination with being 65 years and older, or taking hormone replacement or corticosteroid medications had even higher risk.

The higher cataract risk among the supplement users versus non-users remained evident in analyses that allowed for age by 5-year increments, waist size, education, smoking, alcohol drinking habits, and use of medications such as hormone replacement therapy.

However, the apparent link between vitamin C and cataract risk did not involve vitamin C obtained from fruits and vegetables. The results support cautious use of vitamin C supplements in healthy adults, especially women.