Vitamin E could play a key part in fighting Alzheimer's disease, according to a recent study of the effects of various antioxidants.
The study, published in the 26 June issue of the Journal of the American Medical Association (JAMA), suggests that a diet rich in foods containing vitamin E may help protect some people against the disease - but not when taken as a supplement.
The study was conducted by Martha Clare Morris of the Rush Institute for Healthy Aging at Rush-Presbyterian-St.Luke's Medical Center in Chicago. A related study by Morris and her colleagues, published in the July 2002 Archives of Neurology, also associated vitamin E with protection against more general cognitive decline.
JAMA also reports on a similar study carried out in the Netherlands, which showed that high levels of vitamins C and E in the diet could help protect against the onset of Alzheimer's.
Morris and her colleagues focused on 815 people who were already part of the Chicago Health and Aging Project (CHAP), a study of a large, diverse community of people age 65 and older. All participants were free of dementia at the start of the study and followed for an average of 3.9 years. At an average of 1.7 years from their baseline assessment, participants completed a questionnaire, asking them in detail about the kinds and quantities of foods consumed in the previous year.
Some 131 participants had been diagnosed with Alzheimer's by the end of the study period, when researchers examined the relationship between intake of antioxidants, including dietary and supplemental vitamins E and C, beta carotene and a multivitamin, and the development of the disease. The most significant protective effect was found among people in the top fifth of dietary vitamin E intake (averaging 11.4 IU/d), whose risk of Alzheimer's was 67 per cent lower when compared to people in the group with the lowest vitamin E consumption from food (averaging 6.2 IU/d). The recommended dietary allowance of vitamin E is 22 IU/d.
Morris' team found no significant change in risk of Alzheimer's when the vitamin E was taken as a supplement, or from the other antioxidants and the multivitamin. There was some evidence, though not statistically significant, that increased intake of dietary vitamin C and beta carotene was moving in a "protective direction," the researchers said.
Morris stressed that further research was necessary before any concrete statement could be made about the effects of vitamin E on Alzheimer's, adding that it would be interesting to focus on the link between the vitamin and the apoE status of the sufferers. ApoE is a protein associated with the increased risk of Alzheimer's, and Morris' study suggested that the effects of the vitamin were most pronounced among individuals without the apoE risk factor.
She added that the difference between the effects of dietary and supplemented vitamin E also needed further investigation, as it could be that the supplements simply took longer to take effect than the dietary sources. Another possible explanation might be variations in the forms of vitamin E; most vitamin E supplements consist of alpha tocopherol while foods are generally more rich in gamma tocopherol. These forms of vitamin E scavenge different types of free radicals, with one possibly more important than another in potentially reducing risk of cognitive decline, she said.