The Linxian cataract studies. Two nutrition intervention trials.

OBJECTIVE

To determine whether the vitamin/mineral supplements used in two cancer intervention trials affected the risk of developing age-related cataracts.

DESIGN

Two randomized, double-masked trials with a duration of 5 to 6 years and end-of-trial eye examinations.

SETTING

Rural communes in Linxian, China.

PARTICIPANTS

In trial 1, 2141 participants aged 45 to 74 years, and, in trial 2, 3249 participants aged 45 to 74 years.

INTERVENTIONS

Multivitamin/mineral supplement or matching placebo in trial 1; factorial design to test the effect of four different vitamin/mineral combinations in trial 2 (retinol/zinc, riboflavin/niacin, ascorbic acid/molybdenum, and selenium/alpha-tocopherol/beta carotene).

MAIN OUTCOME MEASURES

Prevalence of nuclear, cortical, and posterior subcapsular cataracts in treatment groups at end of trials.

RESULTS

In the first trial, there was a statistically significant 36% reduction in the prevalence of nuclear cataract for persons aged 65 to 74 years who received the supplements. In the second trial, the prevalence of nuclear cataract was significantly lower in persons receiving riboflavin/niacin compared with persons not receiving these vitamins. Again, persons in the oldest group, 65 to 74 years, benefited the most (44% reduction in prevalence). No treatment effect was noted for cortical cataract in either trial. Although the number of posterior subcapsular cataracts was very small, there was a statistically significant deleterious effect of treatment with riboflavin/niacin.

CONCLUSIONS

Findings from the two trials suggest that vitamin/mineral supplements may decrease the risk of nuclear cataract. Additional research is needed in less nutritionally deprived populations before these findings can be translated into general nutritional recommendations.