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Soy and Cognitive Function: Latest Results

The effect of soyfoods on cognition has been a topic of some controversy. Because soybeans contain isoflavones, which are phytoestrogens, some researchers have theorized that they could prevent cognitive decline that occurs with aging as estrogen is believed to do. However, the results from a Hawaiian population study published in the year 2000 linked soy consumption with greater risk of cognitive impairment (White et al., 2000).

A number of studies since then have challenged the findings from Hawaii. Recently, an expert panel organized by the North American Menopause Society concluded that clinical research suggests soy could favorably impact cognition in women younger than 65, with little effect in older women (2011). The panel also emphasized the need for further research, and especially for larger and longer studies.

That call has been answered with a study by investigators from Stanford University and the University of Southern California Keck School of Medicine (Henderson et al., 2012). In this three-year study, 350 healthy postmenopausal women received either 25 g of soy protein or 25 g of milk protein daily. The soy protein provided 91 mg of isoflavones, the amount found in 3–4 servings of traditional soyfoods. At the end of the study, women who had consumed soy protein showed more improvement in tests of visual memory—the ability to recall pictures. Generally, however, there were no differences between the groups in terms of global cognitive function.

The study is important because of its size and duration. These findings refute concerns that soyfoods could be harmful for cognitive function, although they don’t support the theory that they are protective. However, the study did show heart-health benefits for younger postmenopausal women in that their progression of subclinical atherosclerosis, an indicator of stroke and heart disease risk, was markedly reduced in response to soy intake (Hodis et al., 2011).

It is not clear to me that additional research is justified unless there is reason to believe that a different soy product than the one used in the study in question (isolated soy protein) would have a different effect. And I don’t think that is the case. Having said that, the study in question did find soy improved visual memory and that equol-producers (a bacterially-derived metabolite of the soy isoflavone daidzein) are perhaps more likely to benefit from isoflavones than non-producers. These two issues may be worthy of investigation.

Mark MessinaMark Messina
Adjunct Associate Professor
Department of Nutrition, School of Public Health
Loma Linda University
Executive Director, Soy Nutrition Institute

 

References

Henderson, V.W., St. John, J.A., Hodis, H.N., et al., 2012. Long-term soy isoflavone supplementation and cognition in women: A randomized, controlled trial. Neurology 78: 1841-8.

Hodis, H.N., Mack, W.J., Kono, N., et al., 2011. Isoflavone soy protein supplementation and atherosclerosis progression in healthy postmenopausal women: a randomized controlled trial. Stroke 42: 3168-75.

North American Menopause Society, 2011. The role of soy isoflavones in menopausal health. Menopause 18: 732-53.

White, L.R., Petrovitch, H., Ross, G.W., et al., 2000. Brain aging and midlife tofu consumption. J Am Coll Nutr 19: 242-55.

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