Long-term soy isoflavone supplementation and cognition in women: a randomized, controlled trial.
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.


CONCLUSIONS
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.


METHODS
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.
Departments of Health Research and Policy (Epidemiology) and Neurology and Neurological Sciences, Stanford University, Stanford, CA, USA.
V W
VW
Henderson
J A
JA
St John
H N
HN
Hodis
N
N
Kono
C A
CA
McCleary
A A
AA
Franke
W J
WJ
Mack
D000368:Aged; D000369:Aged, 80 and over; D003071:Cognition / Q000502:physiology*; D019587:Dietary Supplements; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007529:Isoflavones / Q000008:administration & dosage*; D008568:Memory / Q000502:physiology*; D008875:Middle Aged; D017698:Postmenopause / Q000187:drug effects / Q000523:psychology; D030262:Soybean Proteins / Q000008:administration & dosage*; D013997:Time Factors; D016387:Women's Health / Q000706:statistics & numerical data
D007529:Isoflavones; D030262:Soybean Proteins