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In an earlier EduFacts ("Vitamin E and Cataracts: Reviewing the Data") we reviewed two reports of case-control studies documenting decreased risk of cataract / opacity with increased dietary intake of vitamin E. The Lens Opacity Case Control Study evaluated total dietary intake of vitamin E (1). Another case-control study of cataract in Canada (2) evaluated vitamin E supplements. These studies each suggested about a 40-45% decreased risk of cataract or opacity with higher vitamin E intake through diet or supplement use.

Although evidence from these retrospective case control studies is compelling, causality is best documented using prospective study designs. Leske and Chylack and co-authors have recently reported the results of an ongoing prospective study of lens opacity risk factors (3). Briefly, the study utilized data collected on the control patients in the earlier case-control study (1) but used a highly detailed grading scale - the LOCS III - to regrade lens photos at the current study baseline, then to grade lenses again every year over a four year period. This system provided precise measurements of opacity grade to determine new opacities and to precisely grade changes in existing opacities. 744 patients were evaluated. The main nutritional findings in this study are summarized in the 2 figures. During follow-up 24% of patients had increases in nuclear opacities in at least one eye. The risk of an increase in nuclear opacity was 0.43 among users of vitamin E supplements relative to non-users - a decrease in risk of 57%. Those with high (vs low) plasma levels of vitamin E had a 42% decreased risk. The authors also reported a "dose" response relationship between vitamin E supplement use and risk of increased opacity in that decrease in risk was greater with longer use of vitamin E.

References

1. Leske MC, Chylack LT Jr, Wu S. The lens opacities case-control study:risk factors for cataract. Arch Ophthalmol 1991;109:244-251.
2. Robertson JM, Donner AP, Trevithick JR. A possible role for vitamins C and E in cataract prevention. Am J Clin Nutr 1991;53:346S-351S.
3. Leske MC. Chylack LT, He Q, et al. Antioxidant Vitamins and Nuclear Opacites. Ophthalmology 1998; 105:831-836.