Clinical Briefs

With Comments from John La Puma, MD, FACP

Nutrient Intake and Risk of Cataract

October 2001; Volume 4; 120

Source: Jacques PF, et al. Long-term nutrient intake and early age-related nuclear lens opacities. Arch Ophthalmol 2001;119: 1009-1019.

To assess the relation between usual nutrient intake and subsequently diagnosed age-related nuclear lens opacities, 478 nondiabetic women ages 53-73 years from the Boston, MA, area without previously diagnosed cataracts were sampled from the Nurses’ Health Study (NHS) cohort.

Usual nutrient intake was calculated as the average intake from five food frequency questionnaires that were collected during a 13- to 15-year period before the evaluation of lens opacities. The duration of vitamin supplement use was determined from seven questionnaires collected during this same period. Nuclear opacity was defined as a nuclear opalescence grade 2.5 or higher using the Lens Opacification Classification System III.

The prevalence of nuclear opacification was significantly lower in the highest nutrient intake quintile category relative to the lowest quintile category for vitamin C (P < 0.001), vitamin E (P = 0.02), riboflavin (P = 0.005), folate (P = 0.009), beta-carotene (P = 0.04), and lutein/zeaxanthin (P = 0.03). After adjustment for other nutrients, only vitamin C intake remained significantly associated (P = 0.003 for trend) with the prevalence of nuclear opacities. The prevalence of nuclear opacities was significantly lower (P < 0.001) in the highest vitamin C intake quintile category relative to the lowest quintile category (odds ratio [OR], 0.31; 95% confidence interval [CI], 0.16-0.58).

There also were statistically significant trends of decreasing the prevalence of nuclear opacities with increasing duration of use of vitamin C (P = 0.004 for trend), vitamin E (P = 0.03 for trend), and multivitamin (P = 0.04 for trend) supplements. Only duration of vitamin C supplement use remained significantly associated with nuclear opacities after mutual adjustment for use of vitamin E (P = 0.05 for trend) or multivitamin (P = 0.02 for trend) supplements.

The prevalence of nuclear opacities was significantly lower (P = 0.004) for women who used a vitamin C supplement for 10 or more years relative to women who never used vitamin C supplements (OR, 0.36; 95% CI, 0.18-0.72). Plasma measures of vitamins C and E taken at the eye examination also were inversely associated with the prevalence of nuclear opacities.

These results provide additional evidence that antioxidant nutrients play a role in the prevention of age-related nuclear lens opacities.

Comment

The development of most cataracts is now thought to be oxidative in etiology. Though most researchers are uncertain about how much good antioxidant nutrients might do in the prevention of cataract, they’re actively trying to make sense of conflicting reports. And well ahead are patients, who generally are not devouring butternut squash, broccoli, and red bell peppers, but are more than willing to try the multivitamin on sale at CVS (which, by the way, can have real merit).

The Nutrition and Vision Project (NVP) is part of the NHS cohort. This huge epidemiological study is retrospective. It calculates usual nutrient intake, including supplements, from five food frequency questionnaires that were collected during a 13- to 15-year period. Exclusions included those with cataract or diabetes. The cohort was significantly more likely to have fewer pack-years of smoking and was slightly more likely to use vitamin E supplements between 1980 and 1995; the cohort was slightly younger and of a slightly lower body mass index than those excluded—all factors which might bias the results in favor of less cataract formation.

But in the study, there were differences. In the quintile with the lowest nutrient intake for vitamin C (mean, 140 mg), there were the most cataracts; those with the highest intake of vitamin C (mean 362 mg) had the fewest cataracts. The low for vitamin E was 6.7 mg; the high for vitamin E was 91 mg: Cataracts were inversely associated. These levels are based on plasma measurements. In fact, these cataract associations for vitamin C were only true for women with the highest (or the lowest) quintile for more than 10 years, and other antioxidants may contribute.

As the authors say, "a significantly lower risk of opacities is not seen until vitamin C supplements are used for 10 or more years... (and) lutein/zeaxanthin intake above 2.4 mg/d may have a lower risk of nuclear cataract. Lutein and zeaxanthin are the predominant carotenoids found in the human eye lens. However, this association was not clearly independent of the relation between vitamin C and nuclear opacities."

Recommendation

Women at risk for cataract formation may benefit from 300 mg or more of vitamin C daily; given its half-life, it’s advisable to take a day’s vitamin C in divided doses. Two kiwis have double the vitamin C (148 mg) of an average navel orange (75 mg), but the same number of calories. Red and yellow sweet bell peppers have 4-6 times as much vitamin C as green peppers. And they may well be just as good as tablets for cataract prevention. Or better.