Abstract
Background: In a previous trial, treatment with soy isoflavones was
associated with improved nonverbal memory, construction abilities, verbal fluency, and
speeded dexterity compared to treatment with placebo in cognitively healthy older
adults.
Objective: The current trial aimed to examine the potential cognitive
benefits of soy isoflavones in patients with Alzheimer’s disease.
Methods: Sixty-five men and women over the age of 60 were treated with
100 mg/day soy isoflavones, or matching placebo capsules for six months.
APOE genotype was determined for all participants. Cognitive outcomes
and plasma isoflavone levels were measured at baseline, and at two additional time points:
three and six months after baseline.
Results: Of the sixty-five participants enrolled, thirty-four (52.3% ) were
women, and 31 (47.7% ) were APOE
ɛ4 positive. Average age was 76.3 (SD = 7.2) years. Fifty-nine (90.8% )
subjects completed all study visits. Plasma isoflavone levels increased in subjects
treated with soy isoflavones compared to baseline and to placebo, although intersubject
variability in plasma levels was large. No significant differences in treatment effects
for cognition emerged between treatment groups or genders. Exploratory analyses of
associations between changes in cognition and plasma isoflavone levels revealed an
association between equol levels, and speeded dexterity and verbal fluency.
Conclusions: Six months of 100 mg/day treatment with soy isoflavones did not
benefit cognition in older men and women with Alzheimer’s disease. However, our results
suggest the need to examine the role of isoflavone metabolism, i.e., the ability to
effectively metabolize soy isoflavones by converting daidzen to equol when attempting to
fully clarify the cognitive effects of isoflavones.
