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CAN TAKING ANTIOXIDANTS REALLY PREVENT ALZHEIMER DISEASE? (May 2003) Two articles in the June 26, 2002 Journal of the American Medical Association suggest the answer is yes. One is from Rotterdam, the Netherlands, and the other was conducted in the United States. The Rotterdam investigators followed 5,363 men and women, average age 68 years, for six years; the Chicago Health and Aging Project studied 815 men and women, age 65 years and older, over a seven-year period. Their conclusions were: Rotterdam: "high dietary intake of vitamin C and vitamin E may lower the risk of Alzheimer disease". Chicago: "this study suggests that vitamin E from food, but not other antioxidants, may be associated with a reduced risk of Alzheimer Disease". In the Rotterdam study, in the highest vitamin C and vitamin E intake groups, the risk of developing Alzheimer’s was reduced by 34 to 43 percent. In the Chicago study, it was 64 percent reduction for vitamin E from foods, but no reduction for vitamin E from supplements. Commentary: Before anyone gets too excited, here are the problems with drawing too many conclusions from these two perfectly good and well-conducted studies: - One showed benefit from vitamin C, the other did not - The Rotterdam study did not find significant reduction initially, but did for vitamin C after adjusting extensively for other variables (such as education, smoking, energy intake). Vitamin E was of borderline significance after all the adjusting. Usually significance is found before adjusting, and often lessened by adjusting. This reversal of the usual pattern mandates a bit of caution in drawing conclusions. - In the Chicago study, the only group with clear statistically significant reduction in risk was the top 20 percent (top quintile) of vitamin E intake. There was no real dose-response (that is, no increasing benefit as intake increased). If it was the top quintile of vitamin E intake who benefitted, why didn’t vitamin E supplements, (which provide a lot more vitamin E than the diet) reduce the risk of Alzheimer’s? One explanation offered for the finding of a benefit from vitamin E in food, but not in supplements, is that there are two active forms of vitamin E, alpha and gamma. In the diet, vitamin E is in both alpha and gamma forms, whereas in supplements, it is only alpha; it is possible, therefore, that the reduced occurrence of Alzheimer’s from dietary vitamin E, but not from supplements, was due to the gamma form. Of course, before worrying about that possibility, there has to be better evidence that vitamin E in any form reduces the risk of Alzheimer’s. - In the Chicago study, only those negative for a certain genetic pattern benefitted from vitamin E. In the Rotterdam study, even though statistically not significant, there was a definite suggestion of greater benefit from vitamins E and C among those positive for that same genetic pattern. - Neither study found benefit from Beta carotene, but, in the Rotterdam study, the only significant reduction in risk of Alzheimer’s among smokers was found for dietary Beta carotene and flavonoids, not vitamins C and E. These studies then have substantial inconsistencies within and between them. That is also true when comparing them to the few previous studies. One previously published study showed vitamin C supplement use reduced risk and another found no benefit from either vitamin E or vitamin C. These studies are well conducted and do suggest that including lots of antioxidants in the diet might reduce the risk of Alzheimer’s., but there are just too many inconsistencies to allow any judgements or recommendations, at present. Of the antioxidants, vitamins C and E look the most interesting.
We need real intervention studies in which older people are randomized to high or low antioxidant diets and also to vitamin supplements or no supplements, and then are followed for five to ten years. Some have suggested studies should be limited to giving high dosage supplements of vitamins C and E, but we do not know if supplements actually reduce risk of Alzheimer’s; any benefit might be restricted to foods high in antioxidants rather than supplements. The foods have a huge number of potentially beneficial substances other than vitamins E and C, so any benefit might be due to some of these other constituents. The bottom line is: everything is preliminary; lots of inconsistencies; lots of questions; no conclusions possible; no recommendations possible But, Of course, you should eat lots of fruits, vegetables, grains, and nuts that supply plenty of antioxidants and lots of other potentially valuable nutrients. Engelhart, M.J., et al. Dietary intake of antioxidants and risk of Alzheimer Disease Morris, M.C., et al. Dietary intake of antioxidant nutrients and the risk of incident Alzheimer disease in a biracial community study Journal of the American Medical Association. Vol 287 (June 26) Pgs 3223-3237. 2002.
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