Vitamin E and Alzheimer's

Summarized by Robert W. Griffith, MD
April 15, 2005

Introduction

Lots of people take vitamin E supplements, sometimes in the hope of preventing Alzheimer's disease. Recently, however, reports have appeared that show that while a high intake of vitamin E from food sources is linked to a decrease in the occurrence of Alzheimer's, the same is not the case for vitamin E supplements. Vitamin E is composed of 4 different forms of tocopherol (alpha, beta, gamma, and delta), whereas vitamin E supplements usually consist of alpha-tocopherol only. Chicago scientists have therefore studied the possibility that one or more of the non-alpha tocopherol forms might possess a protective effect. The results of their work are reported in the American Journal of Clinical Nutrition, and are summarized here.

What was done

Community residents in the Chicago area aged 65 and over had been involved in a study of food intake and Alzheimer's disease from 1993 to 2002. Over 6,000 residents participated; 62% were white and 38% were black.

In-home interviews were done every 2 years, along with tests of mental ability ('cognitive function'). In addition, some participants were selected at random for physical examination for the presence of diseases (including Alzheimer's) at baseline, and at 2 subsequent interviews.

All the subjects completed food-frequency questionnaires after just over one year into the study. As there was no link found between vitamin E supplements and Alzheimer's in an earlier study, the analysis was limited to food intake only. Some questionnaires had to be eliminated because they reported totally implausible calorie intakes (e.g. over 4,000 calories a day).

The total vitamin E intake included various forms of tocopherol, but was expressed as an 'alpha-tocopherol equivalent' amount. The subjects were classified into five groups, or quintiles, according to their levels of vitamin E intake.

What was found

At baseline, there were no differences between the five quintiles apart from their varying amounts of vitamin E intake.

There were 162 Alzheimer's disease cases in the 1000+ participants who had been clinically examined; and there was decreased mental ability in over 3700 additional subjects, based on cognitive function tests.

Using the occurrence of Alzheimer's disease in the different quintiles, it was shown that higher dietary vitamin E intake was linked to a lesser risk of developing Alzheimer's. After adjusting for differences in age, gender, education levels, and fat intake, there was a 26% reduction for every 5 milligram per day increase in vitamin E intake.

Similarly, higher vitamin E intake was linked to a slower decline in cognitive function over 6 years of follow-up. The decline was about 8.7% per year less for every 5 milligram increase in vitamin E intake.

What about the different tocopherols? The daily intakes of alpha, delta, and gamma tocopherols were significantly linked to a lesser risk of Alzheimer's disease: there were reductions of 34% for alpha, 40% for gamma, and 25% for delta, for every 5 mg/day increased intake, respectively. Beta-tocopherol wasn't linked in this way.

Slower declines in cognitive function were significantly linked to increased alpha and gamma tocopherol intake, but not to the other two tocopherols. Additional analyses showed that the benefits of alpha and gamma were uninfluenced by the amounts of saturated or trans-fatty acids in the diet.

What this means

The findings of this study suggest that the protection offered by dietary vitamin E against Alzheimer's and cognitive decline may be due to the combined intake of the alpha and gamma tocopherol forms. The main sources of vitamin E are vegetable and seed oils. Alpha tocopherol is found in greater amounts in sunflower and wheat germ oils, and gamma tocopherol in com and soybean oils. Of course, proof of the importance of both forms can only come from careful clinical studies in which different groups of participants are given supplements containing one, or the other, or both tocopherols. Such studies will take time. Until their results are available, make sure you eat a good mixture of healthy foods, including plenty of oils from vegetables and seeds.

Source

• Relation of the tocopherols forms to incident Alzheimer disease and to cognitive function. MC. Morris, DA. Evans, CC. Tangney,  et al., Am J Clin Nutr, 2005, vol. 81, pp. 508--514

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