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. CONCLUSION: 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. CLASSIFICATION OF EVIDENCE: 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.

Soy and alfalfa phytoestrogen extracts become potent low-density lipoprotein antioxidants in the presence of acerola cherry extract.

Postmenopausal women have an increased risk of coronary heart disease. Oxidation of low-density lipoprotein (LDL) has been implicated in atherogenesis, and the presence of modified LDL (LDL(-)) in plasma appears to represent LDL oxidation in vivo. Because previous studies have demonstrated a strong antiatherogenic effect of estrogen due to its antioxidant activity and similar antioxidant activity was found for specific isoflavones derived from soy extract, the antioxidant activity of a phytoestrogen extract derived from soy and alfalfa was studied. Copper-mediated LDL oxidation was inhibited in the presence of soy and alfalfa extracts, and this effect was further enhanced in the presence of acerola cherry extract, which is rich in ascorbic acid. Male rabbit aortic endothelial cells pretreated with soy extract were resistant to the toxic effects of high levels of LDL and LDL(-), and a lesser, but significant protection, was also afforded by alfalfa extract. Cell-mediated oxidation of LDL, measured by LDL(-) formation, was inhibited in the presence of soy extract but not alfalfa extract. However, in the presence of acerola cherry extract, both soy and alfalfa extracts potently inhibited the formation of LDL(-). These findings show that acerola cherry extract can enhance the antioxidant activity of soy and alfalfa extracts in a variety of LDL oxidation systems. The protective effect of these extracts is attributed to the presence of flavonoids in soy and alfalfa extracts and ascorbic acid in acerola cherry extract, which may act synergistically as antioxidants. It is postulated that this synergistic interaction among phytoestrogens, flavonoids, and ascorbic acid is due to the "peroxidolitic" action of ascorbic acid, which facilitates the copper-dependent decomposition of LDL peroxides to nonradical products; this synergy is complemented by a mechanism in which phytoestrogens stabilize the LDL structure and suppress the propagation of radical chain reactions. The combination of these extracts markedly lowers the concentrations of phytoestrogens required to achieve significant antioxidant activity toward LDL.

Synergistic inhibition of LDL oxidation by phytoestrogens and ascorbic acid.

Increasing evidence indicates that oxidative modification of low-density lipoprotein (LDL) is an important determinant in atherogenesis, and following menopause, the incidence of coronary heart disease is as prevalent in women as it is in men. Estrogen has been demonstrated to inhibit the susceptibility of LDL to be oxidized, and more recently the use of phytoestrogens has been considered for estrogen replacement therapy. In this study the antioxidant activity of the three major phytoestrogens: genistein, daidzein, and equol were measured in terms of LDL oxidative susceptibility. Increasing levels of genistein, daidzein, and equol inhibited LDL oxidation, and this inhibitory effect was further enhanced in the presence of ascorbic acid. The synergism exhibited by these compounds is of clinical importance to phytoestrogen therapy since the efficacy of phytoestrogens as effective antioxidants is evident at concentration well within the range found in the plasma of subjects consuming soy products. However, this synergism, combined with the low reactivity of the phytoestrogens with peroxyl radicals, suggests that an antioxidant mechanism other then free radical scavenging reactions account for the phytoestrogen antioxidant effect. A structural basis for inhibition of LDL oxidation involving interaction of the phytoestrogens with apoB-100 is postulated.

Effect of supplementary antioxidant vitamin intake on carotid arterial wall intima-media thickness in a controlled clinical trial of cholesterol lowering.

BACKGROUND: There is accumulating experimental, epidemiological, and clinical evidence of an association between anti-oxidant vitamin intake and reduced risk of coronary heart disease. Using data from the Cholesterol Lowering Atherosclerosis Study (CLAS), we explored the association of self-selected supplementary antioxidant vitamin intake on the rate of progression of early preintrusive atherosclerosis. METHODS AND RESULTS: CLAS was an arterial imaging trial in which nonsmoking 40- to 59-year-old men with previous coronary artery bypass graft surgery were randomized to colestipol/niacin plus diet or placebo plus diet. The rate of progression of early preintrusive atherosclerosis was determined in 146 subjects using high-resolution B-mode ultrasound quantification of the distal common carotid artery far wall intima-media thickness (IMT). From the nutritional supplement database, 22 subjects had an on-trial average supplementary vitamin E intake of > or = 100 IU per day (high users) and 29 subjects had an average on-trial supplementary vitamin C intake of > or = 250 mg per day (high users). Within the placebo group, less carotid IMT progression was found for high supplementary vitamin E users when compared with low vitamin E users (0.008 versus 0.023 mm/y, P = .03). No effect of vitamin E within the drug group was found. No effect of vitamin C within the drug or placebo group was found. CONCLUSIONS: Supplementary vitamin E intake appears to be effective in reducing the progression of atherosclerosis in subjects not treated with lipid-lowering drugs while the process is still confined to the arterial wall (early preintrusive atherosclerosis).

Serial coronary angiographic evidence that antioxidant vitamin intake reduces progression of coronary artery atherosclerosis.

OBJECTIVE: To explore the association of supplementary and dietary vitamin E and C intake with the progression of coronary artery disease. DESIGN: A subgroup analysis of the on-trial antioxidant vitamin intake database acquired in the Cholesterol Lowering Atherosclerosis Study, a randomized, placebo-controlled, serial angiographic clinical trial evaluating the risk and benefit of colestipol-niacin on coronary artery disease progression. SETTING: Community- and university-based cardiac catheterization laboratories. SUBJECTS: A total of 156 men aged 40 to 59 years with previous coronary artery bypass graft surgery. INTERVENTION: Supplementary and dietary vitamin E and C intake (nonrandomized) in association with cholesterol-lowering diet and either colestipol-niacin or placebo (randomized). OUTCOME: Change per subject in the percentage of vessel diameter obstructed because of stenosis (%S) determined by quantitative coronary angiography after 2 years of randomized therapy on all lesions, mild/moderate lesions (< 50%S), and severe lesions (> or = 50%S). RESULTS: Overall, subjects with supplementary vitamin E intake of 100 IU per day or greater demonstrated less coronary artery lesion progression than did subjects with supplementary vitamin E intake less than 100 IU per day for all lesions (P = .04) and for mild/moderate lesions (P = .01). Within the drug group, benefit of supplementary vitamin E intake was found for all lesions (P = .02) and mild/moderate lesions (P = .01). Within the placebo group, benefit of supplementary vitamin E intake was not found. No benefit was found for use of supplementary vitamin C exclusively or in conjunction with supplementary vitamin E, use of multivitamins, or increased dietary intake of vitamin E or vitamin C. CONCLUSIONS: These results indicate an association between supplementary vitamin E intake and angiographically demonstrated reduction in coronary artery lesion progression. Verification from carefully designed, randomized, serial arterial imaging end point trials is needed.