Antioxidant vitamin supplementation for preventing and slowing the progression of age-related cataract
Editorial Group: Cochrane Eyes and Vision Group
Published Online: 13 JUN 2012
Assessed as up-to-date: 2 MAR 2012
Copyright © 2012 The Cochrane Collaboration. Published by John Wiley & Sons, Ltd.
How to Cite
Mathew MC, Ervin AM, Tao J, Davis RM. Antioxidant vitamin supplementation for preventing and slowing the progression of age-related cataract. Cochrane Database of Systematic Reviews 2012, Issue 6. Art. No.: CD004567. DOI: 10.1002/14651858.CD004567.pub2.
- Publication Status: New
- Published Online: 13 JUN 2012
Age-related cataract is a major cause of visual impairment in the elderly. Oxidative stress has been implicated in its formation and progression. Antioxidant vitamin supplementation has been investigated in this context.
To assess the effectiveness of antioxidant vitamin supplementation in preventing and slowing the progression of age-related cataract.
We searched CENTRAL (which contains the Cochrane Eyes and Vision Group Trials Register) (The Cochrane Library 2012, Issue 2), MEDLINE (January 1950 to March 2012), EMBASE (January 1980 to March 2012), Latin American and Caribbean Literature on Health Sciences (LILACS) (January 1982 to March 2012), Open Grey (System for Information on Grey Literature in Europe) (www.opengrey.eu/), the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com), ClinicalTrials.gov (www.clinicaltrials.gov) and the WHO International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). There were no date or language restrictions in the electronic searches for trials. The electronic databases were last searched on 2 March 2012. We also checked the reference lists of included studies and ongoing trials and contacted investigators to identify eligible randomized trials.
We included only randomized controlled trials in which supplementation with one or more antioxidant vitamins (beta-carotene, vitamin C and vitamin E) in any form, dosage or combination for at least one year was compared to another antioxidant vitamin or to placebo.
Data collection and analysis
Two authors extracted data and assessed trial quality independently. We pooled results for the primary outcomes, i.e., incidence of cataract and incidence of cataract extraction. We did not pool results of the secondary outcomes - progression of cataract and loss of visual acuity, because of differences in definitions of outcomes and data presentation. We pooled results by type of cataract when data were available. We did not perform a sensitivity analysis.
Nine trials involving 117,272 individuals of age 35 years or older are included in this review. The trials were conducted in Australia, Finland, India, Italy, the United Kingdom and the United States, with duration of follow-up ranging from 2.1 to 12 years. The doses of antioxidant vitamins were higher than the recommended daily allowance. There was no evidence of effect of antioxidant vitamin supplementation in reducing the risk of cataract, cataract extraction, progression of cataract or in slowing the loss of visual acuity. In the pooled analyses, there was no evidence of effect of beta-carotene supplementation in reducing the risk of cataract (two trials) (relative risk (RR) 0.99, 95% confidence interval (CI) 0.91 to 1.08; n = 57,703) or in reducing the risk of cataract extraction (three trials) (RR 1.00, 95% CI 0.91 to 1.10; n = 86,836) or of vitamin E supplementation in reducing the risk of cataract (three trials) (RR 0.97, 95% CI 0.91 to 1.04; n = 50,059) or of cataract extraction (five trials) (RR 0.98, 95% CI 0.91 to 1.05; n = 83,956). The proportion of participants developing hypercarotenodermia (yellowing of skin) while on beta-carotene ranged from 7.4% to 15.8%.
There is no evidence from RCTs that supplementation with antioxidant vitamins (beta-carotene, vitamin C or vitamin E) prevents or slows the progression of age-related cataract. We do not recommend any further studies to examine the role of antioxidant vitamins beta-carotene, vitamin C and vitamin E in preventing or slowing the progression of age-related cataract. Costs and adverse effects should be weighed carefully with unproven benefits before recommending their intake above recommended daily allowances.
Plain language summary
Antioxidant vitamins for preventing and slowing the progression of age-related cataract
A cataract occurs when the normally clear lens in the eye becomes cloudy. Cataracts are the leading cause of correctable reduced vision worldwide. Most cataracts develop slowly with normal aging. However, cataracts also may be related to genetic diseases and medical conditions such as diabetes. Other factors such as poor nutrition, sun damage, radiation, corticosteroids, smoking, alcohol, eye trauma or other eye surgery may influence cataract formation.
Mild or early cataracts may not impair vision. In some cataracts, new eye-glass prescriptions, brighter lighting or magnifying lenses may overcome the vision losses. When these interventions fail to improve poor vision due to cataracts, surgical removal (extraction) is the generally accepted effective treatment. However, cataract surgery is associated with some risks. The estimated annual costs for outpatient, inpatient and prescription drug services related to the treatment of cataract is USD 6.8 billion.
Antioxidant vitamin supplementation has been studied as a means to prevent the formation or to slow the progression of cataract. Results from observational studies have been inconsistent.
The review authors searched for randomized controlled trials in which supplementation with the antioxidant vitamins beta-carotene (provitamin A), vitamin C and vitamin E was compared to inactive placebo or no supplement. Nine trials involving 117,272 adults of age 35 years or older were included in this review. The trials were conducted in Australia, Finland, India, Italy, the United Kingdom and the United States and were of high methodological quality. The doses of antioxidants given in each trial were higher than the recommended daily allowances. The trials provided no evidence of effect of the antioxidant vitamins beta-carotene, vitamin E and vitamin C given alone or in combination on the incidence of cataract, its extraction or progression and on the loss of visual acuity. Some participants (7% to 16%) on beta-carotene developed yellowing of the skin (hypercarotenodermia).