FNOA: Antioxidants (2011-2012)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To test whether consumption of fruit and vegetable juices, containing a high concentration of polyphenols, decreased the risk of incident probable Alzheimer's disease in the Kame Project.

Inclusion Criteria:
  • Age 65 and over
  • Japanese origin
  • Dementia free at baseline.
Exclusion Criteria:

Those with dementia at baseline.

Description of Study Protocol:

Recruitment

The Kame project followed Japanese Americans in King County, Washington form 1992 to 2001 as part of the Ni-Hon-Dea Project, a cross-cultural study of prevalence and incidence rates of Alzheimer's disease and vascular dementia among Japanese populations living in Hiroshima, Japan; Oahu, Hawaii and the metropolitan area of Seattle, Washington. 

Design

Population-based prospective cohort study 

Blinding used 

Not specified 

Intervention

Not applicable

Statistical Analysis

  • Main associations were estimated using hazard ratios (HRs) in Cox proportional hazard regression models adjusted for age
  • Intake of antioxidant vitamins was categorized into tertiles based on the distribution of the cohort. Tea, wine and juice drinking were classified as "less often than once per week, once or twice per week and three times or more per week.
  • Other models were adjusted for years of education as well as dietary intake of vitamins C, E and β-carotene to examine whether the associations between juices, tea and wine and Alzheimer's disease may be attributable in part to such intake from food
  • Stratified analyses by years of education, smoking status, tea-drinking frequency, regular physical activity (yes/no), ApoEε-4 (present/absent and total fat intake (by median) were conducted
  • Multiplicitive interactions also were evaluated in Cox regression models by likelihood ratio tests
  • P values of less than 0.05 (two-sided probability) were interpreted as being statistically significant.

 

Data Collection Summary:

Timing of Measurements

Baseline and four follow-up waves starting at baseline (1992-1994) through 2001.

Dependent Variables

Dementia diagnosis based on Cognitive Abilities Screening Instrument (CASI) and neuropsychologic evaluation using the Consortium to Establish a Registry for Alzheimer's Disease criteria and other tests, as well as dementia criteria in the Diagnostic and Statistical Manual, Fourth Edition.

Independent Variables

  • Fruit and vegetable juice consumption
  • Tea drinking
  • Wine drinking.

Measured by indicator of less often than weekly, one to two times per week or three times or more per week.

Control Variables

  • Sex
  • Smoking
  • Alcohol drinking habits
  • Education
  • Birthplace
  • Place of education before 18 years old
  • Birth date
  • Physical activity
  • BMI
  • Use of antioxidant vitamin supplements and multivitamins in the past month
  • Usual eating preference (Asian or Western)
  • Olfaction diagnostic group (anosmia, microsmia vs. normosmia)
  • Apolipoprotein E (ApoE) status
  • Hypertension
  • Diabetes mellitus.
Description of Actual Data Sample:
  • Initial N: 1,836 subjects
  • Attrition (final N): 1,589
  • Age: Mean age 71.8 years
  • Ethnicity: Japanese
  • Other relevant demographics
    • 54.4% women
    • 6.5% drank sake or wine at least once per week
    • 80% drank tea at least once per week
    • 65% drank fruit or vegetable juices at least once per week
    • 19.9% possess one or more ApoE ε-4 alleles
  • Anthropometrics: Not reported
  • Location: King County, Washington, USA.

 

Summary of Results:

Key Findings

After adjustment for total energy intake, subjects who drank fruit and vegetable juices more frequently had a lower intake of fat and a higher dietary intake of vitamin C, but not vitamin E or β-carotene. They also tended to have a higher educational attainment and more regular physical activity and were more likely to be non-smokers, hypertensive and ApoE ε-4 negative.

  • Tea drinking, the most commonly consumed beverage in the study population, was not associated with Alzheimer’s disease risk
  • Only a small proportion of subjects drank wine and the association with Alzheimer’s disease was inverse but not statistically significant
  • The risk of Alzheimer’s disease was substantially decreased with increasing frequency of intake of juices. Risk was even lower after adjusting for other potential confounding factors.
  • The risk was further reduced after taking into account dietary intake of vitamins E and C and β-carotene with an HR of 0.24 (95% confidence interval [CI], 0.09-0.61) for subjects who drank juices at least three times per week versus those who drank juices less often than once per week (P trend <0.01)
  • The inverse association between fruit and vegetable juices and Alzheimer’s disease appeared in all strata of education, smoking status, tea drinking, regular physical activity, ApoE genotype and total fat intake
  • However, the association tended to be stronger among those who were former or current smokers, drank tea less often, were positive for the ApoE ε-4 and were less physically active
  • Although, no statistically significant interactions were found, the tests for interactions by ApoE genotype (P for interaction, 0.07) and regular physical activity (P for interaction, 0.06) were of borderline significance.
Stratum One to Two Times per Week HR (95% CI) Three Times or more per Week HR (95% CI) P for Trend
Education      
  <12 years  4/25, 0.28(0.02-3.71) 5/103, 0.05(0-0.98)  0.05
 12 years  7/221, 0.51(0.18-1.41) 17/660, 0.2(0.08-0.49)  <0.01
  P for interaction 0.29
Smoking Status      
  Never smokers   7/105, 0.78(0.23-2.61) 14/392, 0.32(0.12-0.84)  0.02
  Ever Smokers  4/141, 0.27(0.06-1.14)  8/365, 0.04(0.01-0.24) <0.01
  P for interaction 0.98
Tea Drinking      
 <3 times per week 2/75, 0.04(0-0.46) 3/223, 0.01(0-0.09)  <0.01
 3 times per week 8/166, (0.19-1.73) 19/527, 0.43(0.17-1.06)  0.06
  P for interaction 0.33
Regular Physical Activity      
 No 4/95, 0.86(0.23-3.2) 6/233, 0.06(0.01-0.23)  <0.01
 Yes 5/147, 0.57(0.16-1.97) 16/507, 0.45(0.16-1.26)  0.13
  P for interaction 0.06
ApoE genotype      
 ApoE-ε4 negative 6/145, 0.93(0.3-2.88)   8/404, 0.25(0.07-0.93) 0.05
 ApoE-ε4 positive 1/30, - 7/80, 0.13 (0.02-0.83) 0.02
  P for interaction 0.07
Total fat intake (grams per day)      
 <29.9 7/132, .76 (.26-2.21)  9/334, 0.23(0.07-0.78)  0.02
 >29.9 4/114, .36 (.07-1.85) 13/429, 0.14(0.04-0.46)  <0.01
   P for interaction .28

 

Author Conclusion:
  • The inverse association between intake of fruit and vegetable juices and Alzheimer's disease cannot be solely explained by antioxidant vitamins
  • Further studies are needed to examine whether components other than antioxidant vitamins such as polyphenols may play a protective role
  • Also, additional studies are needed to confirm the study findings and to investigate how intake of different fruit and vegetable juices relate to the risk of Alzheimer's disease.
Funding Source:
Government: National Institutes of Health, National Institute on Aging
Reviewer Comments:

The authors note the following limitations:

  • Although selection bias was minimized because this was a population-based cohort study, there may still be errors in reporting of dietary intake associated with incipient dementia or dietary changes related to early changes in olfaction. Baseline CASI scores and olfaction diagnostic group in the analysis were adjusted and the analysis was conducted only with participants with at least five years of follow-up.
  • Dietary intake only assessed at baseline
  • Also, although adjustment was made for many potential confounding factors, the possibility of residual confounding may explain the study results
  • The data was limited in sample size
  • Intake information on specific types of juices was not obtained and it was not possible to determine the length of time of juice consumption for needed protective effects to occur.

The use of blinding was not discussed and may have been addressed in the original study.

 

 

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? 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? No
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) N/A
  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? Yes
  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? Yes
  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? ???
  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.) ???
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? ???
  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? 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? ???
  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? 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? ???
  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? 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