Clinical Briefs: Cataract and Antioxidants
Clinical Briefs: Cataract and Antioxidants
With Comments from John La Puma, MD, FACP
Source: A randomized, placebo-controlled, clinical trial of high-dose supplementation with vitamins C and E and beta carotene for age-related cataract and vision loss: AREDS report no. 9. Arch Ophthalmol 2001;119: 1439-1452.
Experimental and observational data suggest that micronutrients with antioxidant capabilities may retard the development of age-related cataract.
To evaluate the effect of a high-dose antioxidant formulation on the development and progression of age-related lens opacities and visual acuity loss, participants were randomly assigned to receive daily oral tablets containing antioxidants (vitamin C, 500 mg; vitamin E, 400 IU; and beta carotene, 15 mg) or no antioxidants. Participants with more than a few small drusen also were randomly assigned to receive tablets with or without zinc (80 mg of zinc oxide) and copper (2 mg of cupric oxide) as part of the age-related macular degeneration trial. Baseline and annual (starting at year 2) lens photographs were graded at a reading center for the severity of lens opacities using the Age-Related Eye Disease Study (AREDS) cataract grading scale.
Primary outcomes were an increase from baseline in nuclear, cortical, or posterior subcapsular opacity grades or cataract surgery, and at least moderate visual acuity loss from baseline (³ 15 letters). Primary analyses used repeated-measures logistic regression with a statistical significance level of P = 0.01. Serum level measurements, medical histories, and mortality rates were used for safety monitoring.
Fifty-six percent of the participants were female, 96% were white, and the median age was 68 years. Of 4,757 participants enrolled, 4,629 (ages 55-80 years) had at least one natural lens present and were followed up for an average of 6.3 years. No statistically significant effect of the antioxidant formulation was seen on the development or progression of age-related lens opacities (odds ratio, 0.97, P = 0.55). There also was no statistically significant effect of treatment in reducing the risk of progression of any of the three lens opacity types or the need for cataract surgery. For the 1,117 participants with no age-related macular degeneration at baseline, no statistically significant difference was noted between treatment groups for at least moderate visual acuity loss. No statistically significant serious adverse effect was associated with treatment.
Use of a high-dose formulation of vitamin C, vitamin E, and beta carotene in a relatively well-nourished older adult cohort had no apparent effect on the seven-year risk of development or progression of age-related lens opacities or visual acuity loss.
Comment
In contrast to the study of age-related macular degeneration (AMD), but founded in part on the same theory (i.e., that cataract formation is an oxidative process that might respond to antioxidant supplementation), this study examined cataracts.
The methods, of course, were the same as in the AREDS study. One quarter of the total participants in the AREDS study were in this cataract prevention arm.
Beta carotene for smokers and former smokers was recognized as potentially injurious, and 117 (2.5% of all participants and 24% of the current smokers) of the participants stopped taking the study medications after being informed of the potential danger. Intention-to-treat analyses were performed on the original grouping.
Disappointingly, no change in visual effect, cataract (regardless of the type of opacity) development, cataract surgery, or other eye events was detected. The only adverse effect noted that was statistically significantly different than placebo was "yellow skin" (from the beta carotene).
As a side note, participants in the antioxidant treatment arms less frequently reported chest pains (19.8% vs. 22.8%, P = 0.01), and were hospitalized significantly less frequently for chest pain, abdominal pain, vasovagal episode, and fever. Conversely, the relative risk estimate of overall mortality among the antioxidant group is in the direction of harm (relative risk = 1.06; 99% confidence interval, 0.84-1.33), but was not significant.
It could be argued that AREDS studied the wrong antioxidants for this purpose—several prospective studies now associate benefit from lutein and zeaxanthin, carotenoids that are stored in the lens. But this information is presented with the benefit of hindsight.
Recommendation
Patients trying to prevent or treat cataract or avoid cataract surgery with supplementation of vitamins C, E, zinc, and beta carotene should be redirected. Those that want to continue should examine supplementation with lutein and zeaxanthin instead.
La Puma J. Cataract and antioxidants. Altern Med Alert 2002;5:24.Subscribe Now for Access
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