The purpose of this study is to determine whether soy supplementation can reduce hardening of the arteries and cognitive decline in postmenopausal women.

Heart disease is the leading cause of death among women in the United States. Atherosclerosis, a primary cause of heart disease, accounts for more than 485,000 heart attacks and 370,000 strokes each year in American women. Data indicate that a woman's risk of suffering from an atherosclerosis-related cardiovascular event significantly increases after menopause; this risk may be due to reduced estrogen production associated with menopause. Soy isoflavones are plant compounds that are structurally similar to human estrogen. Evidence suggests that soy supplements may provide the same protection against heart disease as estrogen in postmenopausal women. This study will determine the effects of soy supplementation on subclinical atherosclerosis progression and cognitive decline in postmenopausal women.

In this double-blinded, placebo-controlled trial, a total of 350 postmenopausal women were randomly assigned to receive either soy protein supplementation or placebo twice daily for 2.7 years. The initial 2.5-year treatment period was increased to 3 years. The active product, given as two divided doses, was 25 g soy protein containing 85 mg aglycone weight naturally-occurring isoflavones (150 mg total isoflavone) of genistein 45 mg aglycone weight (80 mg total weight), daidzein 35 mg aglycone weight (60 mg total weight), and glycitein 5 mg aglycone weight (10 mg total weight). The primary trial end point was the rate of change in the right distal common carotid artery intima-media thickness (CIMT) by ultrasonography. Participants underwent ultrasonography at baseline and every six months along with laboratory determinations and clinical measurements. Cognitive assessments were completed at baseline and the final follow-up visit (2.5 years).

Inclusion Criteria:

• Postmenopausal, defined as no vaginal bleeding for at least 1 year and serum estradiol level lower than 20 pg/ml

Exclusion Criteria:

• Signs, symptoms or personal history of cardiovascular disease
• Diabetes mellitus or fasting serum glucose of 126 mg/dL or greater
• Fasting plasma triglyceride of 500 mg/dL or greater
• Serum creatinine greater than 2.0 mg/dL
• Uncontrolled hypertension
• Untreated thyroid disease
• Life expectancy less than 5 years
• Current use of hormone replacement therapy (HRT)
• Soy, nut, or related food allergies
• More than 5 alcohol drinks per day or substance abuse

Analysis from participants who had at least one follow-up carotid artery intima-media thickness measurement.

Adverse event data were collected for up to 2.5 years for each participant.

At each clinic visit, participants were queried about the occurrence of events since their last clinic visit.