Vitamin C supplements and the risk of age-related cataract: a population-based prospective cohort study in women.

BACKGROUND Experimental animal studies have shown adverse effects of high-dose vitamin C supplements on age-related cataract. OBJECTIVE We examined whether vitamin C supplements (approximately 1000 mg) and multivitamins containing vitamin C (approximately 60 mg) are associated with the incidence of age-related cataract extraction in a population-based, prospective cohort of women. DESIGN Our study included 24,593 women aged 49-83 y from the Swedish Mammography Cohort (follow-up from September 1997 to October 2005). We collected information on dietary supplement use and lifestyle factors with the use of a self-administrated questionnaire. Cataract extraction cases were identified by linkage to the cataract extraction registers in the geographical study area. RESULTS During the 8.2 y of follow-up (184,698 person-years), we identified 2497 cataract extraction cases. The multivariable hazard ratio (HR) for vitamin C supplement users compared with that for nonusers was 1.25 (95% CI: 1.05, 1.50). The HR for the duration of >10 y of use before baseline was 1.46 (95% CI: 0.93, 2.31). The HR for the use of multivitamins containing vitamin C was 1.09 (95% CI: 0.94, 1.25). Among women aged > or = 65 y, vitamin C supplement use increased the risk of cataract by 38% (95% CI: 12%, 69%). Vitamin C use among hormone replacement therapy users compared with that among nonusers of supplements or of hormone replacement therapy was associated with a 56% increased risk of cataract (95% CI: 20%, 102%). Vitamin C use among corticosteroid users compared with that among nonusers of supplements and corticosteroids was associated with an HR of 1.97 (95% CI: 1.35, 2.88). CONCLUSION Our results indicate that the use of vitamin C supplements may be associated with higher risk of age-related cataract among women.