- Click here for explanation of classification scheme.

To clarify the feasibility and potential cognitive efficacy of a soy isoflavone supplement in older adults.

• Men and women
• Age>60 years
• Cognitively healthy
• Free of major medical, neurological, and psychiatric illnesses
• Postmenopausal and not on hormone therapy for at least six months prior to enrollment (females).

• Those with cognitive impairment
• Those with major medical, neurological or psychiatric illnesses.

Recruitment

Participants were recruited from the community; no details on recruitment were provided but were noted to be available at another source.

Design

Randomized placebo-controlled trial 

At baseline, subjects were randomized to receive either capsules containing 100mg per day of purified glycosidic isoflavones (approximately 85% daidzein and genistein) or a matching placebo capsule. Baseline assessment included neuropsychological evaluation, collection of blood samples for isoflavone and hormone assays, and safety laboratory testing, symptom interview, and brief medical evaluation. Subjects completed a standardized and validated food frequency questionnaire, estimating weekly intake of dietary soy isoflavones.

At the start of their research visit, subjects' nonfasting blood samples were drawn for analysis of isoflavones (genistein, daidzein and equol), estrogen (17β-oestradiol), luteinising hormone, and safety laboratory tests (amylase, lipase, and phosphate) Study procedures were repeated at months one, three, and six. Two months following the completion of study medication at month six, subjects returned for a final visit, limited to neuropsychological evaluation and safety laboratory tests.

The neuropsychological measures including sampling memory, attention and executive function (higher order cognitive abilities, such as planning, organizing, and reasoning) following standardized testing procedures.

Blinding used 

This study was described as double-blinded. No other information on blinding was provided.

Intervention

100mg per day of purified glycosidic isoflavones

Statistical Analysis

To examine the feasibility of isoflavone administration, plasma levels of isoflavones were drawn and data on side-effects, safety tests, and and adherence were presented. To examine cognitive effects, neuropsychological data were compared for an effect of soy administration across visits. The effect of soy isoflavone withdrawal was also examined by comparing neuropsychological performance at months six and eight.

Nonparametric methods were employed for all comparisons. P-values were computed for categorical subject characteristics using Pearson's chi-square test, and for continuous subject variables using the nonparametric Wilcoxon rank-sum test. P-values adjusted for age and education for treatment effect across time corresponding to the cognitive outcome measures were computed using non-parametric Wilcoxon score general linear models.

 

Timing of Measurements

• Data was collected at baseline, and at one, three and six months following baseline. An additional visit at eight months following baseline was limited to neuropsychological evaluation and safety laboratory tests.
• Baseline assessment included neuropsychological evaluation, collection of blood samples for isoflavone and hormone assays, and safety laboratory testing, symptom interview, and brief medical evaluation. 
• Two months following the completion of study medication at month six, subjects returned for a final visit, limited to neuropsychological evaluation and safety laboratory tests.

Dependent Variables

• Neuropsychological measures including sampling memory, attention and executive function (higher order cognitive abilities, such as planning, organizing, and reasoning) following standardized testing procedures
• Cognitive performance measured by a battery of tests; tests included measures of verbal and visuospatial memory (Buschke Selective Reminding test, Paragraph Recall, Rey Complex Figure test, Visual Spatial Learning test), language (Boston Naming test), language fluency (FAS, animal fluency), visual-motor function (Rey Complex Figure test copy, Grooved Pegboard) and executive function (Stroop Color Word test, Mazes and Trail Making Test B).
• Serum isoflavone levels (daidzein, genistein, and equol) using stable-isotope dilution CG-MS method.

Independent Variables:

• Subjects were randomized to receive either capsules containing 100mg per day of purified glycosidic isoflavones (approximately 85% daidzein and genistein) or a matching placebo capsule 
• Intake of 100mg per day of soy isoflavones as measured by use of supplements provided at baseline and month three
• Serum isoflavone assays were also performed at months one and six
• Subjects completed a standardized and validated food frequency questionnaire, estimating weekly intake of dietary soy isoflavones.

Control Variables

• Age
• Education.

• Initial N: =31
  • 34 participants were recruited and 31 were enrolled, with one who withdrew after baseline
  • 15 of the participants completing the study were women and 15 were men
    • Eight women in the placebo group
    • Seven women in the isoflavone group
• Attrition (final N): One participant withdrew consent after baseline, making the final n= 30. The gender of the participant who withdrew was not revealed.
• Age: 60-82 years
  • The placebo group was age 74.4 (SD=8)
  • The isoflavone group was age 73 (SD+7.9)
• Ethnicity: All participants were self-identified as white and non-Hispanic
• Other relevant demographics:
  • Education of the placebo group was 16.5 years (SD 3.3)
  • Education of the placebo group was 17.1 years (SD 3.0)
• Anthropometrics: There were no differences between the intervention groups with regard to Mini-Mental State Exam score or Geriatric Depression Scale score.
• Location: Madison, Wisconsin.

 

Key Findings

• The isoflavone group differed across visits from the placebo group on eight of 11 tests administered. Of the 18 variables examined, 10 were statistically significant and two showed a trend toward significance.
• Subjects on the soy isoflavone supplement performed better on several cognitive tests compared with those receiving placebo, including immediate and delayed recall of the Complex Figure Test, category fluency (months three and six only), and grooved pegboard test. There was a trend for improved performance for isoflavone-treated subjects on time to complete mazes.
• At months three and six, subjects on the placebo were faster than those on isoflavones on two tests of executive function, Trail Making Test part B and Stroop Color-Word Test
• The isoflavone and placebo-treated groups differed on the learning trials of the Visual Spatial Learning test. The placebo group was more accurate in recalling correct stimuli, but the isoflavone group was more accurate in rejecting incorrect designs.
• The two groups did not differ in performance on two tests of verbal learning and recall, Buschke Selective Reminding test and Paragraph Recall test, nor on the Boston Naming test
• Plasma levels of genistein and daidzein (P<0.001), but not equol, increased with isoflavone administration.

Change from baseline in cognitive performance over course of 6 months of treatment

	Change at month 1		Change at month 3		Change at month 6		Adjusted P value°
	Isoflavone	Placebo	Isoflavone	Placebo	Isoflavone	Placebo
Visual and Spatial Memory
Total of learning trial-words	1.2(9.1)	-0.5(4.3)	1.9(9.0)	1.4(4.7)	3.1(7.9)	1.4(9.3)	0.42
Learning slope-trial 5 v. trial 1	0.8(2.2)	-0.2(2.1)	-0.3(1.1)	1.1(2.3)	-0.3(2.4)	0.1(1.8)	0.73
Delayed recall-words	0.9(2.3)	-0.0(1.5)	0.7(2.1)	0.1(1.3)	0.9(2.0)	-0.2(1.5)	1.00
Paragraph Recall Test
Total immediate recall-points	0.4(15.6)	-3.0(12.0)	0.9(9.8)	-0.2(13.7)	1.3(14.0)	-1.1(10.9)	0.51
Total delayed recall-points	-3.0(15.3)	-4.0(9.2)	-0.9(10.0)	3.1(10.5)	-0.4(14.0)	-2.0(10.7)	0.33
Rey Complex Figure Test
Immediate recall points	3.9(4.9)	-2.8(6.1)	0.9(4.3)	-0.5(5.5)	2.1(6.5)	-1.3(5.3)	0.00
Delayed recall points	2.4(4.4)	-3.1(4.8)	0.7(4.9)	0.4(5.0)	1.1(5.8)	-0.1(5.3)	0.00
Visual Spacial Learning Test
Total correct positions + designs	2.5(4.8)	3.1(7.4)	-0.1(5.7)	2.7(5.7)	-1.0(5.5)	1.1(5.2)	0.04
Learning slope positions + designs	-0.4(2.0)	0.6(2.7)	-0.4(2.5)	0.5(2.5)	0.1(1.4)	-0.3(2.3)	0.01
Learning slope incorrect designs* (trial 1 vs. trial 5)	0.1(1.6)	0.1(1.2)	-0.6(1.6)	0.30(1.9)	-0.8(1.8)	0.5(2.1)	0.00
Language
Boston Naming (10-item version)	-0.4(4.2)	0.0(7.2)	0.0(5.6)	0.8(5.0)	-0.4(4.8)	1.6(4.8)	1.00
Language Fluency
Fluency
Letter fluency-total	0.9(7.9)	-0.4(7.3)	0.3(7.3)	1.3(6.4)	1.1(9.7)	3.3(6.2)	0.07
Category fluency-total	0.6(6.0)	1.3(9.2)	3.2(5.9)	-0.2(7.8)	1.4(5.8)	-1.9(5.8)	0.00
Visual-motor function
Rey Complex Figure Test copy-points	2.3(3.4)	-10.0(5.1)	0.1(2.6)	0.3(4.1)	0.8(3.6)	-0.6(4.9)	0.01
Grooved Pegboard (ratio of dominant to non-dominant hand-time*)	-0.16(0.5)	-0.03(0.1)	-0.1(0.5)	-0.1(0.2)	-0.23(0.5)	-0.02(0.1)	0.04
Executive function Stroop Color Word Test
Color word time*	0.3(5.0)	0.4(7.2)	-2.1(5.8)	-3.0(7.9)	-2.1(6.5)	-3.5(5.1)	0.02
Trail Marking Test-Time to complete*	-5.4(22.4)	10.2(13.6)	5.6(24.9)	2.9(15.0)	-1.2(18.5)	-5.8(18.7)	0.01
Mazes-Time to complete*	-21.6(44.8)	-11.7(46.1)	-22.1(59.2)	-15.5(44.0)	-23.1(50.6)	-19.3(48.6)	0.09

 °p values for treatment effect across time were adjusted for age and education

*Negative value suggests improvement

Plasma levels of soy isoflavones at baseline, month one and month six

	Placebo treated (n=15)	Isoflavone treated (n=15)	p value
Baseline plasma isoflavone levels1
Total plasma isoflavones (nmol/l) (SD)	16.0(5.5)	21.1(15.7)	0.541
Plasma genistein (nmol/l) (SD)	4.2(1.6)	6.0(5.8)	0.965
Plasma daidzein (nmol/l) (SD)	4.3(2.0)	5.7(4.5)	0.160
Plasma equol (nmol/l) (SD)	7.5(3.1)	9.4(7.5)	0.541
Month 1 plasma isoflavone levels2
Total plasma isoflavones (nmol/l) (SD)	8.4(7.2)	334.6(188.6)	0.000
Plasma genistein (nmol/l) (SD)	2.8(1.6)	173.5(115.0)	0.000
Plasma daidzein (nmol/l) (SD)	2.8(1.3)	157.6(89.8)	0.000
Plasma equol (nmol/l) (SD)	2.8(3.7)	4.7(5.6)	0.089
Month 6 plasma isoflavone levels3
Total plasma isoflavones (nmol/l) (SD)	8.6(3.8)	345.8(183.5)	0.000
Plasma genistein (nmol/l) (SD)	3.1(2.5)	186.5(105.3)	0.000
Plasma daidzein (nmol/l) (SD)	2.9(1.5)	154.9(84.4)	0.000
Plasma equol (nmol/l) (SD)	2.7(0.2)	3.4(3.7)	0.471

¹ For one subject from the placebo-controlled group, plasma isoflavone data were unavailable at baseline

² For one subject from the placebo-controlled group, plasma isoflavone data were unavailable at month one

³ For one subject from the soy isoflavone-treated group, plasma isoflavone data were unavailable at month six

Other Findings

• The effect of withdrawal of isoflavones was examined by comparing the performance of the two groups to their performance two months after the medications were stopped. No significant differences on any cognitive measures were noted.
• There was substantial variability in plasma levels of isoflavones achieved, even with chronic use of a stable dose and standardized time for blood collection.

The authors conclude that 100mg per day of isoflavones was well-tolerated. Plasma genistein and daidzein levels, but not equol, increased with isoflavone administration. Data support the potential cognitive effects of soy isoflavones in older adults.

Data from this study also highlight the need to clarify factors affecting the bioavailability of these compounds as we attempt to understand their cognitive efficacy in older adults.

Government:	National Institutes of Health
University/Hospital:	University of Wisconsin, University of Cincinnati College of Medicine
In-Kind support reported by Industry:	Yes

• Small numbers of subjects in groups. The duration of the study (six months) does not seem adequate to detect cognitive changes in this population.
• There are many factors that could affect cognitive performance in older adults that were not accounted for. Examples include presence of dehydration and use of certain medications.
• Details of recruitment and blinding were not described in this study, so it is difficult to determine if appropriate procedures were followed.