Vitamin E Offers No Protection from Cataracts

By John Gever
BOSTON, 04 may 2008-- Ten years of vitamin E supplements were associated with no effect on cataract development among middle-age and older women, researchers here found.
Among 37,675 participants in the Women's Health Study, involving women 45 and older, 1,159 of those taking vitamin E supplements and 1,217 of those taking placebo developed cataracts, reported William G. Christen, D.Sc., of Brigham and Women's Hospital, and colleagues in the May issue of Ophthalmology.
That worked out to a relative risk of 0.96 (95% CI 0.88 to 1.04), the researchers said.
The Women's Health Study randomized health professionals to 600 IU of vitamin E or placebo every other day, and to 100 mg of aspirin or placebo every other day. Early participants also took beta-carotene. The primary endpoints involved cardiovascular events and cancer. The study began in 1993 and is ongoing.
Because cataracts are thought to arise from oxidative damage to the lens, a number of prospective trials have examined whether vitamin E supplements can prevent them.
None of them identified a benefit, but the longest follow-up in those studies was 6.5 years. Cataracts are slow to develop, and finding a benefit from vitamin E may require a longer trial, Dr. Christen and colleagues said.
Mean follow-up in the Women's Health Study was 9.7 years, with data through March 2004 analyzed in the study.
Participants completed annual questionnaires, which included an item asking whether they had a new diagnosis of cataract or had undergone a cataract extraction.
Those with "yes" answers were asked to give consent for their ophthalmologists or optometrists to be consulted. These professionals then were asked to submit detailed information on the participants' diagnosis and treatment.
Dr. Christen and colleagues obtained adequate information for more than 91% of participants reporting new cataracts.
The data failed to show any effect of vitamin E on subgroups of participants, stratified by age or type of cataract (nuclear sclerosis, cortical, or posterior subcapsular).
Nor did stratification by risk factor reveal a benefit for vitamin E.
Risk factors analyzed in the study included smoking status, alcohol use, body mass index, hypertension, hyperlipidemia, diabetes, menopausal status, use of hormone replacement therapy, parental history of early heart attack, and current multivitamin use.
The only risk-factor subgroups that came close to a significant benefit from vitamin E were those with a parental history of early heart attack (RR 0.80, P=0.08), those with body mass index less than 25 (RR 0.91, P=0.10), and those with hypertension (RR 0.91, P=0.16).
Dr. Christen and colleagues said the apparent lack of effect, while consistent with earlier trials, does not absolutely rule out the possibility that anti-oxidant treatment could help prevent cataracts.
Other researchers have suggested that a barrier forms by middle age that prevents anti-oxidant molecules from reaching the lens nucleus.
"If real, such a barrier might have contributed to the null findings," Dr. Christen and colleagues wrote.
Poor participant compliance seemed unlikely to explain the findings. Thus "averaged throughout the trial, compliance (defined as taking at least two-thirds of the study capsules) was 75.8%, with no difference between the active and placebo groups (P=0.64)," they wrote.
Confounding factors not taken into account in the study design and bias in measuring cataract formation were also possible, though unlikely, the researchers said.
Dr. Christen and colleagues noted that several large ongoing trials are also testing anti-oxidants for preventing eye disease, including the Physicians' Health Study II, a male counterpart to the Women's Health Study.
Data from the large Nurses' Health Study in 2005 found that participants taking vitamin E supplements had slower progression of cataracts. However, that was a retrospective analysis derived from nutrient intake questionnaires, and participants decided on their own whether to take supplements.
The Women's Health Study analysis was funded by the National Institutes of Health. The Women's Health Study is sponsored by the National Heart, Lung, and Blood Institute.
No potential conflicts of interest were reported.

Primary source: OphthalmologySource reference:Christen W, et al "Vitamin E and age-related cataract in a randomized trial of women" Ophthalmology 2008; 115: 822-29.