EAL

FNOA: Antioxidants (2011-2012)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To examine the association between rates of cognitive change and dietary consumption of fruits and vegetables among older persons.

Inclusion Criteria:

Participants of the Chicago Health and Aging Project, aged 65 years and older
Only analyzed participants who had at least two cognitive assessments and who had completed a food frequency questionnaire.

Exclusion Criteria:

Potentially invalid food frequency questionnaire data (implausible energy intake, more than half of the items missing)
Persons who completed the food frequency questionnaire more than 2.5 years after the baseline interview and had only two cognitive assessments.

Description of Study Protocol:

Recruitment

The Chicago Health and Aging Project was a 1993-to-2002 cohort study of older residents from a geographically defined population of the south side of Chicago
Door-to-door census identified 8,501 residents aged 65 years and older; 439 died and 249 moved before participation could be secured
Of 7,813 remaining surviving residents, 6,158 agreed to participate in 90-minute home interviews
All study participants were contacted for follow-up at three and six years.

Design

Prospective cohort study.

Statistical Analysis

Linear mixed effects models used to test the hypothesis that fruit and vegetable consumption would slow the rate of within-person decline in cognitive score over six years
The best model of the important confounding variables was determined by considering non-linear and interaction associations with both initial cognitive score and rate of change.

Data Collection Summary:

Timing of Measurements

Participants completed the food frequency questionnaire and were administered at least two of three cognitive assessments at baseline, three-year and six-year follow-ups
Interviewers administered cognitive tests during in-home interviews.

Dependent Variables

Cognitive function assessed through the average Z-score of four tests:

East Boston Tests of immediate memory and delayed recall
Mini-Mental State Examination
Symbol Digit Modalities Test.

Independent Variables

Vegetable and fruit consumption assessed through 139-item modified version of the Harvard semi-quantitative food frequency questionnaire.

Control Variables

Age
Sex
Race
Education
Frequency of participation in cognitive activities
Physical activity
Cigarette smoking
Daily consumption of alcohol
History of heart disease, hypertension, stroke, or diabetes mellitus
Medications.

Description of Actual Data Sample:

Initial N: 6,158 agreed to participate in 90-minute home interviews
Attrition (final N): 4,930 survived to the three-year follow-up. 3,718 participants in the final analysis (38% male, 62% female)
- 217 were excluded due to potentially invalid food frequency questionnaire data
- 455 were excluded due to completing food frequency questionnaire 2.5 years after baseline interview
Age: Mean age 74.3 years (range 65 to 102 years)
Ethnicity: 60% African American, 40% Caucasian
Other relevant demographics: Mean 12.2 years of education
Anthropometrics: Analyzed cohort had higher global cognitive scores (mean 21.1 vs. -2.2) and slightly higher Mini-Mental State Examination scores (26.7 vs. 25.3) than the entire study population at baseline
Location: Chicago, IL.

Summary of Results:

Key Findings

Persons with high intakes of fruits and vegetables tended to have a favorable risk profile for health and cognition, were more likely to be female, to be Caucasian, to have more years of education and to have higher levels of physical activity
The mean cognitive score at baseline for the analyzed cohort was 0.18 (range -3.5 to 1.6) and the overall mean change in score per year was a decline of 0.04 standardized units
Average total daily intake of fruits and vegetables was 4.5 servings per day (range zero to 14.4); the average number of vegetable servings per day was 2.3 (range zero to 8.2) and average number of fruit servings per day was 2.2 (range zero to 8.5).
In mixed effects models adjusted for age, sex, race and education, compared with the rate of cognitive decline among persons in the lowest quintile of vegetable intake (median of 0.9 servings per day), the rate for persons in the fourth quintile (median of 2.8 servings per day) was slower by 0.019 standardized units per year (P=0.01), a 40% decrease, and by 0.018 standardized units per year (P=0.02) for the fifth quintile (median of 4.1 servings per day), or a 38% decrease in rates
The association remained significant (P for linear trend =0.02) with further control of cardiovascular-related conditions and risk factors
Fruit consumption was not associated with cognitive change.

Multiple-adjusted Differences in the Rates of Cognitive Change by Quintile of Fruit and Vegetable Intake

Variables	Quintile 1	Quintile 2	Quintile 3	Quintile 4	Quintile 5	P for Trend
Green leafy vegetables	0	0.009	0.014	0.016	0.018	0.03
Yellow vegetables	0	0.012	0.915	0.025	0.011	0.34
Cruciferous vegetables	0.004	0.002	0.002	0.022	0.12	0.09
Legumes	0	-0.001	0.008	---	0.005	0.39
Citrus fruits and fruit juices	0	-0.000	-0.003	0.001	0.001	0.92

Author Conclusion:

Greater consumption of vegetables was associated with slower rate of cognitive decline over six years in this large community-based population of older persons. The decrease in rate for persons who consumed greater than two vegetable servings per day was equivalent to about five years of younger age. Of the different types of vegetables, green leafy vegetables had the strongest association. Fruit consumption was not associated with cognitive change.

Funding Source:

Government:

National Institute on Aging

Reviewer Comments:

Almost half of the cohort was not included in the analysis. Analyzed cohorts had higher global cognitive scores and slightly higher Mini-Mental State Examination scores than the entire study population at baseline.
Authors note the following limitations:
- Number of participants were not included in the analysis because their dietary questionnaires were obtained midway into the study or they were invalid
- Dietary assessments not obtained at baseline for a number of the analyzed participants
- Absence of information on apolipoprotein E (APOE) genotype on the entire cohort for analysis.

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)	N/A
	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)	N/A

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?	???
	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?		???
	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?	???
	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?	???
	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?		N/A
	5.1.	In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate?	N/A
	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.)	N/A
	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?		Yes
	6.1.	In RCT or other intervention trial, were protocols described for all regimens studied?	N/A
	6.2.	In observational study, were interventions, study settings, and clinicians/provider described?	Yes
	6.3.	Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect?	Yes
	6.4.	Was the amount of exposure and, if relevant, subject/patient compliance measured?	N/A
	6.5.	Were co-interventions (e.g., ancillary treatments, other therapies) described?	N/A
	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?	N/A
	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?		???
	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?	Yes
	7.4.	Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures?	???
	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?		Yes
	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?	Yes
	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)?	N/A
	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?	N/A
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