Long-term soy isoflavone supplementation and cognition in women
What this study found
Long-term ISP did not improve global cognition in healthy postmenopausal women. The primary global cognition outcome at 2.5 years was not significant: mean standardized difference 0.11, 95% CI -0.13 to 0.35, p = 0.36. Visual memory showed a favorable secondary effect for ISP (mean standardized difference 0.33, 95% CI 0.06-0.60), but other cognitive factors and individual tests were not significantly different. Overall, the findings do not support ISP for global cognitive benefit in this population.
- Study & population
- Randomized, placebo-controlled trial in healthy postmenopausal women, including natural and surgical menopause, conducted at the University of Southern California in Los Angeles.
- Intervention
- The active intervention was 25 g/day of isoflavone-rich soy protein (ISP) taken orally as powder or bar form for 2.5 years, providing 91 mg/day aglycone-weight isoflavones (total isoflavone equivalents 154 mg/day; genistein 52 mg, daidzein 36 mg, glycitein 3 mg).
- Key limitation
- Attrition reduced the analyzed sample relative to randomization in both arms, and cognitive benefit was limited to a secondary endpoint.
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Open PDFOriginal 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.