Tofu and Alzheimer’s Disease

By now, you may have heard of the Honolulu Heart Study and the associated study by Dr. White and colleagues. Spurred on by preliminary findings from the study, a link between tofu and alzheimer’s disease was made much of in various media sources. So, should you be concerned about eating tofu? Worried that you’ll “catch” something? Well, we did some research into the subject to see how credible the link is.

Turns out, there’s more to these preliminary results than the superficial comments that arise from it. Here’s an overview of the study with some revealing insights.

Research on Tofu and Cognitive Function is published in April’s issue of the Journal of the America College of Nutrition

Overview

Dr. White and colleagues conducted an observational study utilizing participants of a study established in 1965 for research on heart disease, stroke, and cancer. Food consumption information was available on selected foods from interviews conducted in 1965-1967 and 1971-1974. Cognitive functioning was tested using the Cognitive Abilities Screening Instrument (CASI) in 1991-1993 when participants were aged 71 to 93 years (n=3734). Brain atrophy was assessed using neuroimage and autopsy information for a sample of the participants. Cognitive function information was also analyzed for wives of a sample of study participants who had been living with the participants at the time of their dietary interviews.

Results

Poor cognitive test performance, enlargement of ventricles and low brain weight were significantly associated with higher midlife tofu intake.

Study Conclusion

In this population, higher midlife tofu consumption is associated with indicators of cognitive impairment and brain atrophy in late life. The authors hypothesize that isoflavones may have an adverse effect on brain aging by competing with estrogen.

Inconsistencies in Dr. White’s article:

 

  • The highest tofu consumers had several common traits that could impact cognitive functioning
    • These study participants were older, had fewer years of education, and were born in Japan. They were more likely to retain traditional Japanese dietary practices.
    • These men experienced more strokes than low tofu consumers did.
    • Those autopsied were older at death, shorter, and had higher midlife systolic blood pressure.
  • The authors attempted to address the above issues, but they cannot eliminate the possibility that their results may be due to some other unidentified factor related to both tofu intake and brain aging.
  • This study cannot show cause and effect. Tofu may merely be a marker for some other unfavorable exposure that led to brain aging.
  • The influence of age, education and history of stroke accounted for 27.8% of the variance in CASI scores. Tofu intake only accounted for 2.3 – 3.1% of the variation.
  • We do not know how tofu influences estrogen levels in the brain. In fact, research has not consistently shown that low estrogen levels are related to cognitive function.
  • The results presented in Dr. White’s paper are preliminary. The number of subjects with high tofu consumption was small. The confidence intervals around the odds ratios are wide, indicating the limited precision of these results.
  • Much more research is needed before definitive conclusions can be reached about the role of tofu in cognitive functioning.

White, LR, et al. Brain Aging and Midlife Tofu Consumption, Journal of the American College of Nutrition, Vol. 19, No. 2, 245-252.

In contrast to the White findings, John Robbins points out that “dementia rates are lower in Asian countries (where soy intake is high) than in western countries. We know that the Japanese lifestyle (with its high soy intake) has long been associated with longer life span and better cognition in old age. And we know that Seventh Day Adventists, many of whom consume soyfoods their whole lives, have less dementia in old age than the general population.” Certainly, the cultures where soyfoods are consumed on a regular basis don’t see corresponding raises in levels of Alzheimer’s — certainly it’s never been reported in either Japan or China, for example.

He also points out that a doctor practising in Hawaii followed up on this study by comparing the levels of aluminum (high levels of which are commonly associated with Alzheimer’s) in island and mainland tofu and found much higher levels in the island sources. In fact, he found that aluminum is used in refining some of the sources of soyfoods in Hawaii.

So, do you need to worry about the effects of tofu on your brain? It certainly wasn’t proved by this study and hasn’t been shown by any others. In fact, tofu can form part of a healthy diet that features fruits, vegetables, and reduced amounts of saturated fats. In fact, studies on Alzheimer’s have found links to low levels of folic acid — which can be alleviated by eating more leafy green vegetables. As well, a number of animal studies have indicated that soy protein helps protect the brain from the oxidative damage of free radicals, which one theory suggests is the cause of Alzheimer’s Disease. Another theory is that decreased blood flow to the brain, or ischemia, is the cause of the disease, but animal studies again suggest that soy protein reduces the risk of this damage occurring.