A one-year trial of soy protein supplements with isoflavones produced no beneficial effects on cognitive function in postmenopausal women age 60 years or older, according to an article in the July 7th issue of the Journal of the American Medical Association. The one-year trial also found no benefits on bone mineral density or plasma lipids.

The abrupt decrease in estrogen after menopause is associated with acceleration of several processes linked to aging, including declines in bone mineral density and cognitive function and an increase in low-density and total cholesterol. Isoflavones, estrogen-like compounds naturally occurring in plant foods, have been suggested as an alternative for traditional estrogen therapy with fewer adverse effects.

Sanne Kreijkamp-Kaspers, M.D., Ph.D., and her Dutch colleagues conducted a study with 202 healthy postmenopausal women aged 60 to 75 years between April 2000 and September 2001. Women were randomized to 25.6 grams soy protein containing 99 mg of isoflavones or placebo (total milk protein as a powder), each of which could be mixed with food or beverages on a daily basis for 12 months. Cognitive testing, bone mineral density, and plasma lipids were tested at baseline and at the final visit, one year later.

"In this longer-term, relatively large double-blind, placebo-controlled , randomized trial, we did not find any effect of soy protein supplementation, which naturally contains large amounts of isoflavones, on cognitive function, bone mineral density, or plasma lipids in the relevant population of aging women," the authors reported.

Timing of the supplementation may provide an explanation for the difference in findings from this study compared to previous ones that were more promising, the authors wrote: "…the most pronounced effects of estrogen on cognitive function have been reported in perimenopausal women, and not in late postmenopausal women. With respect to bone, it has been suggested that it is easier to prevent changes or losses after menopause than reverse them when they have already taken place. The influence of the timing of supplementation needs to be elucidated in further research."