The Erasmus Medical Center team believe that dietary antioxidants might counteract the detrimental effects of oxidative stressors, such as the free radicals produced by smoking. A previous study had shown that patients taking vitamin E supplement had a slower progression of Alzheimer's disease than patients taking placebo.
Dr Marianne Engelhart and colleagues investigated whether intake of a range of antioxidants from food - including beta-carotene, flavonoids, vitamin C and vitamin E - was associated with Alzheimer's disease risk. The team studied 5,395 individuals aged 55 and older who were free of dementia at baseline. The participants were re-examined twice during the six-year follow-up period and were continuously monitored for incident dementia and dietary intake. Over the course of the study, 197 of the participants developed dementia and, of these, 146 were diagnosed with Alzheimer's disease.
To evaluate the associations of dietary intake of antioxidants with risk of Alzheimer's disease the researchers controlled for factors such as age, sex, alcohol intake, education, smoking habit, body mass index, calorific intake and cardiovascular comorbidity. After adjusting for these variables, the team found that high intake of vitamins C and E was linked to a lower Alzheimer's risk, and that the protective effect of the antioxidants was greatest in current smokers.
Dr Engelhart and colleagues believe there may be several mechanisms behind the protective effect of antioxidants. Firstly, antioxidants may decrease the level of oxidative stress in the brain, thereby reducing the amount of DNA damage, neuronal cell death and beta-amyloid aggregation. Secondly, antioxidants may reduce the risk of atherosclerosis - a known risk factor for dementia.
The team said that further research is needed to understand the relationship between Alzheimer's disease risk and dietary antioxidant intake. In an accompanying editorial in the Journal of the American Medical Association, Dr Daniel Foley from the US National Institute on Aging and Dr Lon White from the Pacific Health Research Institute, Hawaii, said that the findings were inconclusive, but that the hypothesis "makes sense". "We continue to hope that when the final answer is established, it will be that the development of Alzheimer's disease can be delayed or prevented by dietary intake," they said. Reference: Engelhart et al, JAMA 2002;287:3223-3229
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