Soy-based products have long been touted as a treatment for menopausal symptoms.  However, many of the clinical studies measuring the effectiveness of dietary sources of soy isoflavones (e.g., soy beverages, soy powder) for the treatment of menopausal vasomotor symptoms (i.e., hot flushes, night sweats) have been negative.  Less is known about the effects of soy on cognition.  A large clinical trial suggests that soy may not have any positive effects on cognition in postmenopausal women.

In this double-blind, placebo-controlled trial, the Women’s Isoflavone Soy Health (WISH) trial, 350 healthy postmenopausal women were randomized to receive either soy supplements or placebo (milk protein). The soy supplement contained 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). Cognitive ability was estimated at baseline with the Wechsler Test of Adult Reading.  Cognitive functioning was compared between the two groups at 2.5 years.

Adherence to the study protocol (monitored by assessment of blood and urine soy isoflavones at 6-month intervals) was nearly 90% for both groups. 313 women (age range, 45–92; mean age, 61) were included in an intention-to-treat analysis.  The two groups did not differ significantly on a composite score of global cognition. Secondary analyses revealed a small effect on visual memory scores but no significant differences on other cognitive subscores.

The WISH trial is the largest study, and the longest in duration, assessing the effects of soy isoflavones on cognition.  Its findings are consistent with previous clinical trials, including a large study of Dutch women (60–75 years) treated with isoflavones for one year.  While some have hypothesized that younger postmenopausal women may benefit from soy products more than older postmenopausal women; however, in the WISH study, women younger than 60 and women within 5 years of menopause did not show any benefits from soy supplements in terms of cognitive functioning.  These results indicate that soy isoflavone supplementation is unlikely to improve cognitive functioning in postmenopausal women of any age.

Ruta Nonacs, MD PhD

Henderson VW, St John JA, Hodis HN, et al. Long-term soy isoflavone supplementation and cognition in women: A randomized, controlled trial. Neurology 2012 Jun 5; 78:1841.