The prospective Rotterdam Study involved 5,395 people over age 55 with no dementia at baseline. All of the participants, who lived in one section of the Rotterdam area, provided dietary information when the study began in 1990.
The researchers previously reported a similar association of vitamin E intake with a lower risk of dementia and Alzheimer's disease over six years of follow-up among the cohort.
The current study found that after 9.6 years of follow-up, 465 of the participants had developed dementia; 365 of these cases were classified as Alzheimer's disease.
Higher baseline vitamin E consumption correlated with lower long-term risk of dementia in models minimally adjusted for age only and those adjusted for age, education, apolipoprotein genotype, total caloric intake, alcohol and smoking habits, body mass index, and use of supplements (both P=0.02 for trend).
Dietary surveys indicated that margarine was by far the biggest contributor to vitamin E intake at 43.4%, followed by sunflower oil at 18.5%, butter at 3.8%, and cooking fats at 3.4%.
Participants with vitamin E intakes in the top third, averaging 18.5 mg per day, were 25% less likely to develop dementia of any kind over almost 10 years of follow-up than those in the bottom third, who averaged only 9.0 mg per day. Higher baseline vitamin E consumption correlated with lower long-term risk of dementia (both P=0.02 for trend).
While the top versus bottom tertile comparison was significant, the middle group with vitamin E intake averaging 13.5 mg per day was no less likely to develop dementia than the lowest intake group.
For Alzheimer's disease alone, the multivariate-adjusted risk was 26% lower among those with the highest intake compared with the lowest (95% confidence interval 3% to 44%, P=0.03 for trend). But intermediate intake again appeared to have no impact.
Other antioxidants — vitamin C, beta-carotene, and flavonoids — held no significant associations with dementia or Alzheimer's disease risk (multivariate adjusted P=0.50 to >0.99 for trend).
Sensitivity analyses excluding participants who reported taking supplements at baseline showed similar results.
The researchers noted that the vitamin intakes seen in the study were consistent with a typical Western diet but cautioned about the possibility of residual confounding in the observational results.