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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.
GLOSSARY
- CI=
- confidence interval;
- ISP=
- isoflavone-rich soy protein;
- WISH=
- Women's Isoflavone Soy Health
Footnotes
Study funding: Supported by the National Center of Complementary and Alternative Medicine, the Office of Dietary Supplements, and the Office of Research on Women's Health (NIH grant U01-AT001653). Solae LLC (St. Louis, MO) provided study products without charge.
WISH Research Group Coinvestigators are listed on the Neurology® Web site at www.neurology.org.
Supplemental data at www.neurology.org
- Received November 8, 2011.
- Accepted January 31, 2012.
- Copyright © 2012 by AAN Enterprises, Inc.
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