Men receiving daily supplements of the isoflavones performed significantly better in tests of their working memory, report scientists from the University of South Australia and the University of Adelaide in the British Journal of Nutrition.
The beneficial effects may be related to the oestrogenic effects of the isoflavones, said the researchers, noting that the improvements were in cognitive processes “which appear dependent on oestrogen activation”.
Researchers, led by Peter Howe, recruited 34 healthy men to participate in their 12-week double-blind, placebo-controlled cross-over trial. The men were randomly assigned to receive a daily dose of 116 mg soy isoflavones, providing 68 mg daidzein, 12 mg genistein, and 36 mg glycitin, or placebo for 6 weeks. They were subsequently crossed-over to the other intervention for the following 6 weeks.
Tests of memory, mental function, and visual-spatial processing performed before and after the supplementation period showed that the isoflavone supplements were associated with improved spatial working memory; “a test in which females consistently perform better than males”, said the researchers.
Indeed, men receiving the isoflavones required 18 per cent fewer attempts to correctly complete the tasks, committed 23 per cent fewer errors, and achieved the tasks in 17 per cent less time than they did during the placebo phase.
However, the researchers note that the soy had no apparent effect on either auditory or episodic memory, executive function, or visual-spatial processing.
“Isoflavone supplementation in healthy males may enhance cognitive processes which appear dependent on oestrogen activation,” they stated.
Commenting on the possible mechanism, Howe and his co-workers noted that it has already been reported that females “perform better in certain memory-related tasks than males”. This has been attributed to differences in circulating oestrogen levels. The female hormone interacts with certain receptors in the hippocampus, frontal lobe and cortex of the brain that play a role in mental function.
Remembering other studies
Previously, Italian scientists reported that isoflavone supplements may improve both mood and mental function in post-menopausal women - a group of women with reduced levels of oestrogen (Fertility and Sterility, Vol. 85, pp. 972-978), while French researchers reported that increased intakes of flavonoids, of which isoflavones are on such sub-category, may reduce the loss of cognitive function that occurs naturally with age (American Journal of Epidemiology, Vol. 165, pp. 1364-1371).
Source: British Journal of Nutrition
Published online ahead of print, First View article, doi:10.1017/S0007114509990201
“Soya isoflavone supplementation enhances spatial working memory in men”
Authors: A.A. Thorp, N. Sinn, J.D. Buckley, A.M. Coates, P.R.C. Howe