Antioxidants and Age-related Cataracts
February 2000; Volume 23
Source: Brown L, et al. A prospective study of carotenoid intake and risk of cataract extraction in US men. Am J Clin Nutr 1999;70:517-524.
Dietary antioxidants, including carotenoids, are hypothesized to decrease the risk of age-related cataracts by preventing oxidation of proteins or lipids within the lens. We examined the association between carotenoid and vitamin A intakes and cataract extraction in men.
We included U.S. male health professionals (n = 36,644) who were 45-75 years of age in 1986 in this prospective cohort study. Others were subsequently included as they became 45 years of age. A detailed dietary questionnaire was used to assess intake of carotenoids and other nutrients, and was mailed to respondents every two years until and including 1994. Age, smoking, and other potential cataract risk factors were controlled for.
During eight years of follow-up, 840 cases of senile cataract extraction were documented. We observed a modestly lower risk of cataract extraction in men with higher intakes of lutein and zeaxanthin but not of other carotenoids (alpha-carotene, beta-carotene, lyco-pene, and beta-cryptoxanthin) or vitamin A after controlling for other potential risk factors including age and smoking.
Men in the highest fifth of lutein and zeaxanthin intake had a 19% lower risk of cataract relative to men in the lowest fifth (relative risk: 0.81; 95% confidence interval [CI] 0.65-1.01; P for trend = 0.03). Among specific foods high in carotenoids, broccoli and spinach were most consistently associated with a lower risk of cataract. Lutein and zeaxanthin may decrease the risk of cataracts severe enough to require extraction, although this relation appears modest in magnitude.
More than a million cataract extractions are performed annually. Are foods high in lutein and zeaxanthin able to reduce this number and improve vision? Lutein is found in green leafy vegetables, especially spinach and kale, and in broccoli.
A parallel prospective study (Am J Clin Nutr 1999;70:509-516) by the same investigator group examined the dietary recalls of 77,466 nurses from 1980 through 12 years of follow-up. Those with the highest intake of lutein and zeaxanthin had a 22% reduced risk of cataract extraction compared with those in the lowest quintile.
How might antioxidants prevent cataracts? By blocking the oxidative modification of lens protein or by preventing lipid peroxidation within the epithelium of the lens? Why carot-enoids? Lutein and zeaxanthin are accumulated by ocular tissues; when extra lutein and zeaxanthin are taken as supplements, macular pigment increases. What about other carotenoids? In these studies, no other carotenoid made a difference, and neither did vitamin A, whether in supplements or in food.
Weaknesses of this data include the weaknesses of all recalled dietary data (even from middle-aged and elderly health professionals).
Although the lack of randomized controlled data of either supplements or food is real, high antioxidant food consumption may be something people can do to reduce their risk of cataracts. As a reminder about where much of the public is on this, Visionade (stocked with lutein, bilberry, and ginkgo, and blended with blueberry and cranberry juices) is now on the shelves of some health food stores.
More spinach made Popeye strong, and only two servings per week appears to reduce relative risk of cataract extraction. Sauté spinach over high heat with a little olive oil, sliced garlic cloves, and coins of fresh ginger for extra flavor. Hold off on lutein supplements.