Age and Ageing Advance Access originally published online on December 2, 2008
Age and Ageing 2009 38(1):86-93; doi:10.1093/ageing/afn227
A preliminary study of the safety, feasibility and cognitive efficacy of soy isoflavone supplements in older men and women
1 Section of Geriatrics and Gerontology, Department of Medicine, University of Wisconsin, Madison, WI 53705, USA
2 Geriatric Research, Education and Clinical Center (GRECC), William S. Middleton Memorial Veterans Hospital, Madison, WI 53705, USA
3 Department of Biostatistics and Medical Informatics, University of Wisconsin, Madison, WI 53792-4675, USA
4 Wisconsin Alzheimer's Institute, University of Wisconsin, Madison, WI 53719, USA
5 Department of Pathology and Laboratory Medicine, Cincinnati Children's Hospital Medical Center, and Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH 45267, USA
Address correspondence to: C. E. Gleason, Madison VA GRECC (11G), 2500 Overlook Terrace, Madison, WI 53705, USA. Tel: (+1) 608 256 1901, Ext. 11518; Fax: (+1) 608 280 7165. Email: ceg{at}medicine.wisc.edu
Background: a small number of reports exist on the cognitive effects of soy isoflavones, the findings from which are mixed. Isoflavone efficacy is dependent upon conversion of glycosides contained in soy foods and supplements to the biologically active aglycons. Of particular interest is the production of the metabolite, equol, which is dependent upon intestinal microflora and an integrous digestive system, both being altered by age and age-associated conditions. Unfortunately, few studies enrolled adults over the age of 70, and none included older men.
Objective: we examined safety, feasibility and cognitive efficacy of soy isoflavone administration in older nondemented men and women (age 62–89 years).
Design and Methods: in this randomised, placebo-controlled, double-blind pilot study, subjects ingested either 100 mg/day soy isoflavones (glycoside weight) or matching placebo tablets for 6 months.
Results: active and placebo-treated subjects exhibited a comparable side-effect profile. Plasma levels of genistein and daidzein (P < 0.001), but not equol, increased with isoflavone administration. While similar at baseline, the two groups differed across 6 months of treatment on 8 of 11 cognitive tests administered. Isoflavone-treated subjects improved on tests of visual-spatial memory (P < 0.01) and construction (P = 0.01), verbal fluency (P < 0.01) and speeded dexterity (P = 0.04). Placebo-treated participants were faster than isoflavone-treated subjects on two tests of executive function (P < 0.05).
Conclusions: these data suggest that administration of 100 mg/day of isoflavones was well tolerated. Plasma genistein and daidzein levels, but not equol, increased with isoflavone administration. Finally, data support the potential cognitive effects of soy isoflavones in older adults.
Keywords: cognitive ageing, phytoestrogen, isoflavone, equol, genistein, daidzein, elderly
Received 7 December 2007; accepted in revised form 10 July 2008.