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Multi-Nutrient Supplements and Cataract
A number of prospective epidemiologic studies have reported a lower occurrence of cataract in regular users of multi-vitamin and mineral supplements (1-3).
The Physicians' Health Study noted significantly fewer self-reported cataracts or confirmed cataract surgery in multi users during 5 years of follow-up. The Longitudinal Study of Cataract found that regular multi users reduced their risk of nuclear opacification by one-third. Finally, taking a multi for 10 years or more was reported to lower the risk of nuclear and cortical cataracts in the Beaver Dam Eye Study. In contrast, the Nurses' Health Study found no association between multi-supplement use and incidence of cataract extraction (4).
The cataract portion of the AREDS trial also failed to show an effect of high dose antioxidants on the risk of development or progression of lens opacities. However, a recent prospective cohort analysis of AREDS has found that consistent use of a multi-vitamin and mineral supplement may delay the progression of lens opacities (5).
Study Design and Methods
There were 4596 participants enrolled in the AREDS cataract trial, half of whom were assigned to high-dose antioxidants and half to no antioxidants. Two-thirds of the subjects elected to take a multi vitamin and mineral supplement containing RDA-level potencies that was offered to all participants.
Lens photographs at baseline and at 5 to 6 years follow-up were compared. An "any" lens opacity event was defined as the occurrence of change from baseline of specified amounts of nuclear, cortical, or posterior subcapsular opacity, or the performance of cataract surgery.
The AREDS researchers used a propensity score approach to provide a means of adjusting for selection bias that may have occurred with the elective use of the multi supplement and for confounding. The use of propensity scores tends to produce unbiased estimates of treatment effects. It balances the covariates between treatment groups, much as trials use randomization to achieve balance. Risk of progression to a lens event was assessed by odds ratios (OR) with 95% confidence intervals (CI).
With adjustment for propensity score and baseline covariates, the risk of development of or progression to any cataract was reduced by 16% in regular multi takers (OR = 0.82, CI = 0.71-0.95, p = 0.025). For nuclear cataract, a 25% risk reduction was observed in the multi-supplement users (OR = 0.75, CI = 0.61-0.91, p = 0.004). (See Table)
There was a similar reduction in risk of cortical lens events, although significance was not reached. No beneficial effect was seen for posterior subcapsular opacities.
Individual nutrients have been linked to a lower risk of various cataract types including vitamins C and E, lutein, and the B-vitamins riboflavin and thiamin. Rather than supplementing with only a few, high-dose antioxidants, it may be that supplementation with a broad-spectrum of nutrients is a more effective strategy. The NEI in fact, is currently supporting a controlled trial of more than 1000 subjects in Italy to assess the effect of multi use on development and progression of cataracts. Median follow-up is 7 years, with completion likely this year. References
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