Long-term soy isoflavone supplementation and cognition in women

Neurology

Jun 2012

DOI: 10.1212/WNL.0b013e318258f822

Citations:109

Influential Citations:5

Interventional (Human) Studies

Enhanced Details

Methods

Design: randomized, double-blind, parallel-group, placebo-controlled trial. Participants: healthy postmenopausal women, aged 45-92 years. 350 randomized (175 ISP, 175 placebo); 313 with baseline and end cognitive data included in intention-to-treat analyses.

Intervention

Daily 25 g of isoflavone-rich soy protein (ISP) for 2.5 years; ISP contained 91 mg aglycone weight isoflavones (52 mg genistein, 36 mg daidzein, 3 mg glycitein); administered as powder or bar form.

Results

Global cognition did not differ between ISP and placebo after 2.5 years (mean standardized change 0.42 vs 0.31; difference 0.11, 95% CI -0.13 to 0.35). Visual memory favored ISP (mean difference 0.33, 95% CI 0.06 to 0.60). No significant differences in other cognitive factors or tests; younger postmenopausal women showed no clear benefit. Post hoc analyses suggested a non-significant trend for 5–10 years postmenopause to show greater improvement with ISP. Surgically menopausal women on ISP performed worse than those on placebo (mean difference -0.78; 95% CI -1.53 to -0.02). Consistent equol producers showed a nonsignificant trend toward greater improvement (approx. 0.34; 95% CI -0.04 to 0.72). Overall, there is Class I evidence that long-term ISP does not improve global cognition in healthy postmenopausal women; possible domain-specific (visual memory) benefit requires replication. High soy intake at this level appears safe for memory, with uncertain applicability to younger women, men, or equol producers.

Limitations

Subgroup analyses (e.g., surgically menopausal status, equol producer status) were underpowered; cognitive outcomes were secondary endpoints; generalizability may be limited to healthy postmenopausal women.

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. show less