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Cognitive improvement after 6 weeks of soy supplements in postmenopausal women is limited to frontal lobe function

File, Sandra E. BSc, PhD, DSc1; Hartley, David E. BSc, PhD1; Elsabagh, Sarah BSc, PhD1,3; Duffy, Rosanna BSc, PhD2; Wiseman, Helen BSc, PhD2

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Objective: To assess the effects of 6 weeks of treatment with soy supplements on mood, menopausal symptoms, and cognition in postmenopausal women not taking other forms of hormone therapy.

Design: In a double-blind, placebo-matched parallel groups study, 50 postmenopausal women (aged 51-66 y) were randomly allocated to receive daily treatment with a soy supplement (Novasoy, 60 mg total isoflavone equivalents/day) or matching placebo capsules. They were tested at baseline before treatment began and after 6 weeks of treatment in tests of attention, memory, and frontal lobe function, and completed questionnaires to assess sleepiness, mood, and menopausal symptoms.

Results: After 6 weeks of treatment, there was a significant (P < 0.02) reduction in somatic menopausal symptoms in the group taking soy supplements, but there were no other significant effects of soy on menopausal symptoms or mood. On the test of nonverbal short-term memory, the soy group showed greater improvement than the placebo group (P < 0.03), but there were no effects of soy on long-term memory, category generation, or sustained attention. However, the soy treatment produced significantly better performance on the two tests of frontal lobe function, those of mental flexibility (simple rule reversal, P < 0.05; complex rule reversal, P < 0.03) and of planning ability (P < 0.05).

Conclusions: The results suggest that the main improvement after 6 weeks of soy supplementation was in frontal lobe function. Significant improvements in the same three measures of frontal lobe function were previously found after 12 weeks of soy supplements in postmenopausal women. The effects of soy on memory seem less robust.

Six weeks of treatment with soy supplements has beneficial effects on measures of frontal lobe function (mental flexibility and planning) in postmenopausal women. In addition, a reduction in somatic menopausal symptoms is seen in soy-treated women.

From the 1Psychopharmacology Research Unit, Centre for Neuroscience, Hodgkin Building, King's College London, Guy's Campus, London, UK; 2Department of Nutrition & Dietetics, Franklin-Wilkins Building, King's College London, UK; and 3The School of Pharmacy, Brunswick Square, London, UK.

Received February 3, 2003; revised and accepted April 13, 2004.

This study was supported by a grant from the Dunhill Medical Trust.

Address correspondence to: David Hartley, Psychopharmacology Research Unit, Center for Neuroscience, Hodgkin Building, King's College London, Guy's Campus, London SE1 1UL, UK. E-mail: David.2.Hartley@kcl.ac.uk

©2005The North American Menopause Society