Long-term Soy Isoflavone Supplementation and Cognition in Women: A Randomized, Controlled Trial

Neurology. 2012 Jun 5;78(23):1841-8. doi: 10.1212/WNL.0b013e318258f822.

Abstract

Objective: To determine the cognitive effects of long-term dietary soy isoflavones in a daily dose comparable to that of traditional Asian diets.

Methods: In the double-blind Women's Isoflavone Soy Health trial, healthy postmenopausal women were randomly allocated to receive daily 25 g of isoflavone-rich soy protein (91 mg of aglycone weight of isoflavones: 52 mg of genistein, 36 mg of daidzein, and 3 mg glycitein) or milk protein-matched placebo. The primary cognitive endpoint compared between groups at 2.5 years was change from baseline on global cognition, a composite of the weighted sum of 14 neuropsychological test score changes. Secondary outcomes compared changes in cognitive factors and individual tests.

Results: A total of 350 healthy postmenopausal women aged 45-92 years enrolled in this trial; 313 women with baseline and endpoint cognitive test data were included in intention-to-treat analyses. Adherence in both groups was nearly 90%. There was no significant between-group difference on change from baseline in global cognition (mean standardized improvement of 0.42 in the isoflavone group and 0.31 in the placebo group; mean standardized difference 0.11, 95% confidence interval [CI] -0.13 to 0.35). Secondary analyses indicated greater improvement on a visual memory factor in the isoflavone group (mean standardized difference 0.33, 95% CI 0.06-0.60) but no significant between-group differences on 3 other cognitive factors or individual test scores, and no significant difference within a subgroup of younger postmenopausal women.

Conclusion: For healthy postmenopausal women, long-term dietary soy isoflavone supplementation in a dose comparable to that of traditional Asian diets has no effect on global cognition but may improve visual memory.

Classification of evidence: This study provides Class I evidence that long-term dietary supplementation with isoflavone-rich soy protein does not improve global cognition of healthy postmenopausal women.

Publication types

  • Comparative Study
  • Randomized Controlled Trial
  • Research Support, N.I.H., Extramural

MeSH terms

  • Aged
  • Aged, 80 and over
  • Cognition / physiology*
  • Dietary Supplements*
  • Double-Blind Method
  • Female
  • Humans
  • Isoflavones / administration & dosage*
  • Memory / physiology*
  • Middle Aged
  • Postmenopause / drug effects
  • Postmenopause / psychology
  • Soybean Proteins / administration & dosage*
  • Time Factors
  • Women's Health* / statistics & numerical data

Substances

  • Isoflavones
  • Soybean Proteins