Just about a year ago, this blog addressed the relationship between soy and cognitive function, a controversial topic given some of the older epidemiologic findings.1,2 The blog post ended by referring to a recent review of the literature that concluded: “The evidence to date is not sufficient to make any recommendations about the association between dietary intake of soy isoflavones and cognition in older adults.”3 While that statement remains true, two new studies, one an epidemiologic study and the other an intervention study, suggest the evidence is moving in the direction of soy exerting cognitive benefits.
The aforementioned epidemiologic study included 1,105 Taiwanese participants aged 65 and over who completed the Short Portable Mental Status Questionnaire (SPMSQ), which measured cognitive function.4 In addition to filling out the SPMSQ, all participants provided extensive information on their dietary habits by filling out a food frequency questionnaire and by indicating the foods they consumed within the past 24 hours. Of the more than 1,000 participants, 85.6% reported eating soyfoods at least once per day.
The researchers divided the men and women in this study into three groups according to their soy intake: none, <1 time per day or ³1 time per day. After adjusting for a wide range of variables that could impact cognition, the results indicated that in comparison to not consuming soy, those who ate soy less than 1 time per day were 43% (relative risk, 0.57; 95% confidence interval: 0.32, 1.03) less likely to be cognitively impaired and those eating soy at least daily were 55% (relative risk, 0.45; 95% confidence interval: 0.25, 0.81) less likely to be cognitively impaired. The latter finding was statistically significant. The major limitation of this epidemiologic study is its cross-sectional design.