EAL

FNOA: Antioxidants (2011-2012)

Citation:

Study Design:

Class:

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Quality Rating:

Research Purpose:

The purpose of this study was to assess the effects of soy isoflavones (in food and dietary supplements) on cognitive functioning in relatively young, healthy, postmenopausal women. It was hypothesized that treatment with either the dietary supplement or soy isoflavones would improve cognitive performance, whereas the placebo treatment would result in no change in cognitive performance over the course of the study.

Inclusion Criteria:

Postmenopausal women
Have not menstruated for at least one year
Have not received hormone replacement therapy (HRT) for at six months.

Exclusion Criteria:

Those who received hormone replacement therapy (HRT) in the past six months.

Description of Study Protocol:

Recruitment

Subjects were recruited as part of a larger study. Participants were recruited within two small communities where two large universities are located. Participants responded to local advertisements that appeared in newspaper, radio, pharmacies, physician's offices, retails stores, churches, or university news announcements. Participants were paid $100.00 for their participation upon completion of the study

Design

Randomized, placebo-controlled trial

Participants were randomly assigned to one of three groups: Control (cow's milk and placebo supplement), soy milk (soy milk and placebo supplement), and soy supplement group (cow's milk and isoflavone supplement). Prior to the intervention, participants adhered to a four-week adjustment diet that minimized intake of foods containing isoflavones. Following this, a 16-week intervention began. Groups of 20-15 participants began the study at the same start date and a new group of participants started the study every four weeks, creating five periods. Participants in each period were matched by age and IQ and then randomized into three groups.

A 24-hour urine collection was obtained at baseline (week zero) and test (week 16).

Participants consumed 706mL of milk daily for 16 weeks. The isoflavone supplement contained 70mg/isoflavone per day (30mg daidzein, 33mg genistein, and 7mg glycitein).

A dietitian provided individual instruction and written guidelines to the women regarding replacement of usual dairy or other similar food items with the study milk to allow for consistent macronutrient intake and prevention of weight gain during the study. Compliance was measured via personal communication, dietary records, and the appearance of isoflavone metabolites in the urine.

Cognitive functioning was assessed using several tasks that measure behavioral responses. These tasks were performed at baseline and test (week 16). Tests included tests of selective attention (the Stroop task) and Memory (Working Memory Digits Ordering, Color Matching, Memory Recall and Recognition, Visual Pattern Recognition, and Memory Span). Because cognitive performance can be influenced by depression, the Beck Depression Inventory was administered at baseline and test to screen for depression.

Blinding used

The study was described as double-blind, but no details on the blinding were provided.

Intervention

706mL of soy milk or 70mg per day of isoflavone (30mg daidzein, 33mg genistein, and 7mg glycitein)

Statistical Analysis

Isoflavone concentration and the study population (age, IQ, BDI, education, number of years since last menstruation, body mass index (BMI), and exercise) were characterized using descriptive statistics. Group comparisons were conducted using a one-way, between subjects, ANOVA for unbalanced design or a chi square analysis. To discern unadjusted differences between test and baseline measures within each group for each cognitive test, paired-difference T-tests were used. To evaluate whether there was a differential improvement in cognitive function for women in the different treatment groups, a between-subject multivariate ANOVA was conducted on the difference scores between tests and baselines means for each treatment group. This was carried out on each cognitive task except the Stroop test. A mixed design ANOVA with one between-subjects factor and two within-subject factors were used for the Stroop test.

Data Collection Summary:

Timing of Measurements

A four-week adjustment diet was administered prior to the intervention. Data was collected at baseline (week zero) and test (week 16).

Dependent Variables

Cognitive changes as measured by a battery of cognitive testing that assessed behavioral responses for selective attention and memory
Cognitive functioning was assessed using several tasks that measure behavioral responses. Tests included tests of selective attention (the Stroop task) and Memory (Working Memory Digits Ordering, Color Matching, Memory Recall and Recognition, Visual Pattern Recognition, and Memory Span). Because cognitive performance can be influenced by depression, the Beck Depression Inventory was administered at baseline and test to screen for depression.

Independent Variables

Participants were randomly assigned to one of three groups: Control (cow's milk and placebo supplement), soy milk (soy milk and placebo supplement), and soy supplement group (cow's milk and isoflavone supplement). Prior to the intervention, participants adhered to a four-week adjustment diet that minimized intake of foods containing isoflavones. Following this, a 16-week intervention began.
Participants consumed 706mL of milk daily for 16 weeks. The isoflavone supplement contained 70mg/isoflavone per day (30mg daidzein, 33mg genistein, and 7mg glycitein).
A dietitian provided individual instruction and written guidelines to the women regarding replacement of usual dairy or other similar food items with the study milk to allow for consistent macronutrient intake and prevention of weight gain during the study. Compliance was measured via personal communication, dietary records, and the appearance of isoflavone metabolites in the urine.

Control Variables

Age
IQ
Period (start date of intervention)
Education
Current exercise level.

Description of Actual Data Sample:

Initial N: 79, all female
- 25 in the soy milk group
- 27 in the soy supplement group
- 27 in the control group
Attrition (final N): All participants completed the study, making the final n=79.
Age: Participants ranged in age from 48-65 years of age, with an average of 56.1 years. No significant differences were found by group with respect to age.
- The soy group was age 56.1±0.9
- The supplement group was 55.7±0.7
- The control group was 56.4±0.8
Ethnicity: No information was provided
Other relevant demographics: No significant differences were found by group with respect to IQ, levels of depression, education, number of years since last menstruation, and levels of exercise. All participants were free of major health conditions, were non-smokers, did not have legume allergies, had no recent antibiotic therapy, or a history of gallstones. None had a history of dementia, psychiatric disorders, or movement disorders. All had normal color vision and corrected-to-normal visual acuity.
Anthropometrics: No significant differences were found by group with respect to BMI.
- The BMI of the soy group was 26.8±1.2
- The supplement group was 28.2±0.9
- The control group was 28.5±1.3
Location: Two small communities where two large universities are located, in Washington State.

Summary of Results:

Key Findings

At baseline, total isoflavone concentration was not detectable in each group. At the end of the study, both the soy milk and supplement users had detectable isoflavone concentrations that were not statistically different.
Postmenopausal women showed no improvement on the cognitive tasks chosen to assess short-term memory, long-term memory, working memory, or selective attention based on the intervention.
Soy isoflavones did not benefit selective attention (assessed by the Stroop task), visuo-spatial short-term memory recall (assessed by the BVRT), or long-term pattern recognition (assessed by the pattern recognition task) or visuo-spatial working memory (assessed by the color match task).
No differential improvements in cognitive functioning were found in these tasks at test relative to baseline for women in the soy milk, supplement, or control groups.

Mean ±SEM reaction time (RT; in ms) and percent accuracy (AC) performance in the selective attention (Stroop) task conditions for each treatment group at both baseline and test.

Variables	Soy Milk n=25		Treatment Group Supplement (n=27)		Control (n=27)
Testing Baseline
Conditions	RT	AC	RT	AC	RT	AC
Incompatible	821±126	97.9±2.3	799±91	96.7±3.1	821±135	94.5±9.7
Neutral	640±73	99.6±1.4	624±90	99.9±0.6	642±112	99.7±1.0
Compatible	648±96	100±0	635±114	99.6±1.3	645±122	99.9±0.6
Test
Conditions	RT	AC	RT	AC	RT	AC
Incompatible	817±120	97.4±3.4	801±97	97.5±3.8	787±123	98.1±3.4
Neutral	634±84	99.8±0.8	615±63	99.8±0.8	651±88	99.7±1.0
Compatible	637±92	99.8±0.8	639±85	99.5±1.4	640±90	99.4±1.4

Mean±SEM performance at baseline and test in the different memory tasks for each treatment group. Only the Digit Ordering task showed a significant change in performance across the treatment groups.

Cognitive Tasks	Soy Milk	Treatment Group Supplement	Control
Digit ordering	n=25	n=26	n=27
Total Error Baseline^a	9.8±1.3	9.9±1.3	9.9±1.3
Total Error Test^a	13.1±1.3	9.2±1.3	8.6±1.3
Color Matching	n=17	n=23	n=19
Total Error Baseline^a	34.1±7.5	41.9±7.5	35.0±7.5
Total Error Test^a	33.1±7.5	39.0±7.5	31.9±7.5
RT (sec) Baseline^a	207±25.9	189±25.9	188±25.9
RT (sec) Test^a	166±25.9	150±25.9	148±25.9
Benton Visual Retention Test	n=25	n=27	n=25
Total Error Baseline^a	5.2±0.7	4.8±0.7	3.8±0.7
Total Error Test^a	4.4±0.7	4.4±0.7	3.6±0.7
Total Correct Baseline^b	6.6±0.4	6.9±0.4	7.4±0.4
Total Correct Test^b	6.7±0.4	7.1±0.4	7.5±0.4
Visual Pattern Test Recognition	n=25	n=27	n=25
Percent Correct Baseline^b	80.0±2.5	85.9±2.5	87.8±2.5
Percent Correct Test^b	93.4±2.5	95.0±2.5	94.8±2.5
Forward Digit Span	n=25	n=27	n=27
Total Correct Baseline^b	8.3±0.5	8.5±0.5	8.2±0.5
Total Correct Test^b	8.3±0.5	8.9±0.5	8.6±0.5
Corsi Block-Tapping	n=25	n=27	n=27
Total Correct Baseline^b	4.8±0.3	4.0±0.3	4.7±0.3
Total Correct Test^b	4.9±0.3	4.8±0.3	4.9±0.3

Author Conclusion:

The authors conclude that this study found that the consumption of isoflavones in supplement form or dietary form (soy milk) over a 16-week period did not have an appreciable effect on attention or memory in healthy, postmenopausal women.

Funding Source:

Government:	Washington State Attorney General's Office
University/Hospital:	Washington State University
In-Kind support reported by Industry:	Yes

Reviewer Comments:

Authors note that the small sample size and short intervention used may have contributed to some of the insignificant results, as well as the fact that compliance to the intervention was relatively subjective
Data on use of medications was not collected (or not reported in this paper). Use of certain medications can affect cognitive status.

Quality Criteria Checklist: Primary Research
Relevance Questions
	1.	Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies)	Yes
	2.	Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about?	Yes
	3.	Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice?	Yes
	4.	Is the intervention or procedure feasible? (NA for some epidemiological studies)	Yes

Validity Questions
1.	Was the research question clearly stated?		Yes
	1.1.	Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified?	Yes
	1.2.	Was (were) the outcome(s) [dependent variable(s)] clearly indicated?	Yes
	1.3.	Were the target population and setting specified?	Yes
2.	Was the selection of study subjects/patients free from bias?		???
	2.1.	Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study?	Yes
	2.2.	Were criteria applied equally to all study groups?	Yes
	2.3.	Were health, demographics, and other characteristics of subjects described?	Yes
	2.4.	Were the subjects/patients a representative sample of the relevant population?	???
3.	Were study groups comparable?		Yes
	3.1.	Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT)	Yes
	3.2.	Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?	Yes
	3.3.	Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.)	Yes
	3.4.	If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis?	N/A
	3.5.	If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.)	N/A
	3.6.	If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")?	N/A
4.	Was method of handling withdrawals described?		Yes
	4.1.	Were follow-up methods described and the same for all groups?	Yes
	4.2.	Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.)	Yes
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	Yes
	4.4.	Were reasons for withdrawals similar across groups?	N/A
	4.5.	If diagnostic test, was decision to perform reference test not dependent on results of test under study?	N/A
5.	Was blinding used to prevent introduction of bias?		Yes
	5.1.	In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate?	Yes
	5.2.	Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.)	Yes
	5.3.	In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded?	N/A
	5.4.	In case control study, was case definition explicit and case ascertainment not influenced by exposure status?	N/A
	5.5.	In diagnostic study, were test results blinded to patient history and other test results?	N/A
6.	Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described?		???
	6.1.	In RCT or other intervention trial, were protocols described for all regimens studied?	Yes
	6.2.	In observational study, were interventions, study settings, and clinicians/provider described?	N/A
	6.3.	Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect?	No
	6.4.	Was the amount of exposure and, if relevant, subject/patient compliance measured?	Yes
	6.5.	Were co-interventions (e.g., ancillary treatments, other therapies) described?	Yes
	6.6.	Were extra or unplanned treatments described?	N/A
	6.7.	Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups?	Yes
	6.8.	In diagnostic study, were details of test administration and replication sufficient?	N/A
7.	Were outcomes clearly defined and the measurements valid and reliable?		Yes
	7.1.	Were primary and secondary endpoints described and relevant to the question?	Yes
	7.2.	Were nutrition measures appropriate to question and outcomes of concern?	Yes
	7.3.	Was the period of follow-up long enough for important outcome(s) to occur?	No
	7.4.	Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures?	Yes
	7.5.	Was the measurement of effect at an appropriate level of precision?	Yes
	7.6.	Were other factors accounted for (measured) that could affect outcomes?	Yes
	7.7.	Were the measurements conducted consistently across groups?	Yes
8.	Was the statistical analysis appropriate for the study design and type of outcome indicators?		???
	8.1.	Were statistical analyses adequately described and the results reported appropriately?	Yes
	8.2.	Were correct statistical tests used and assumptions of test not violated?	Yes
	8.3.	Were statistics reported with levels of significance and/or confidence intervals?	No
	8.4.	Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)?	No
	8.5.	Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)?	Yes
	8.6.	Was clinical significance as well as statistical significance reported?	Yes
	8.7.	If negative findings, was a power calculation reported to address type 2 error?	???
9.	Are conclusions supported by results with biases and limitations taken into consideration?		Yes
	9.1.	Is there a discussion of findings?	Yes
	9.2.	Are biases and study limitations identified and discussed?	Yes
10.	Is bias due to study's funding or sponsorship unlikely?		Yes
	10.1.	Were sources of funding and investigators' affiliations described?	Yes
	10.2.	Was the study free from apparent conflict of interest?	Yes