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Citation:

Miura K, Greenland P, Stamler J, Liu K, Daviglus ML, Nakagawa H.  Relation of vegetable, fruit, and meat intake to 7-year blood pressure change in middle-aged men: the Chicago Western Electric Study. Am J Epidemiol 2004;159: 572-580.


PubMed ID: 15003961
Study Design:
Prospective Cohort Study
Class:
B - Click here for explanation of classification scheme.
POSITIVE: See Research Design and Implementation Criteria Checklist below.
Research Purpose:

To examine relations of food intake to seven-year blood pressure change.

Inclusion Criteria:

Participants from Chicago Western Electric Study.

Exclusion Criteria:
  • Missing baseline dietary assessments or baseline blood pressure or educational attainment
  • Previously-diagnosed diabetes mellitus
  • Prior myocardial infarction (MI) 
  • Fewer than three follow-up examinations between 1960 and 1966.
Description of Study Protocol:

Recruitment

  • Subjects recruited from the Chicago Western Electric Study, a long-term prospective population study principally of coronary heart disease (CHD) and its precursors
  • In 1957, 3,102 men were randomly selected from the 5,397 men aged 40 to 55 years, employed for at least two years at the Hawthorne Works of the Western Electric Company in Chicago.

Design

Prospective cohort study.

Statistical Analysis

  • Analyses were conducted with a generalized estimating equation method for longitudinal data to estimate the relation of baseline dietary factors to average yearly change in systolic blood pressure (SBP) or diastolic blood pressure (DBP)
  • Analyses were serially adjusted for confounders in five estimating equations
  • Average values of baseline blood pressure by baseline food group intake, adjusted for age and other confounders, were also compared using ANCOVA.
Data Collection Summary:

Timing of Measurements

In 1958 and 1959, blood pressure was measured and nutrient intake assessed by comprehensive interview. Intake of 26 specific food groups also assessed. Blood pressure was re-measured annually through 1966, as well as weight, serum cholesterol, medical history and physical exam, electrocardiogram and other items described previously.

Dependent Variables

Blood pressure measured with standard sphygmomanometers.

Independent Variables

Dietary intake obtained twice, one year apart, by nutritionists using standardized interviews and questionnaires.

Control Variables

  • Age
  • Weight at each year
  • Alcohol consumption
  • Calories
  • Other Foods
  • Height
  • Education
  • Smoking.
Description of Actual Data Sample:
  • Initial N: Originally 2,107 participants, before exclusion criteria was applied
  • Attrition (final N): 1,710 employed men
  • Age: Initially, 41 to 57 years
  • Ethnicity65% were first or second generation Americans predominantly of German, Polish or Bohemian ancestry. Most other men were descendants of Great Britain and Ireland
  • LocationChicago.
Summary of Results:

Other Findings

  • Average SBP/DBP increase was 1.9/0.3mmHg per year and average weight gain was 0.6 pounds per year
  • Using most models, SBP of men who consumed 14 cups to 42 cups of vegetables in a month (0.5 cups to 1.5 cups per day) vs. less than 14 cups a month (less than 0.5 cups per day) was estimated to rise 2.8mmHg less in seven years (P<0.01)
  • In all models, the SBP of men who consumed 14 cups to 42 cups of fruit per month vs. less than 14 cups a month was estimated to increase 2.2mmHg less in seven years (P<0.05)
  • In all models, beef, veal, lamb and poultry intakes were related directly to a greater SBP/DBP increase (P<0.05).
Author Conclusion:

The main findings in this seven-year blood pressure follow-up study of middle-aged employed men are as follows:

  1. Higher intakes of vegetables and of fruits were related to less of an increase in SBP and DBP over time, independent of age, weight at each year and intake of other foods
  2. Men with a higher intake of red meat (beef, veal, lamb and pork) had a significantly greater increase in blood pressure
  3. Men with a higher poultry intake had a significantly greater annual increase in blood pressure, independent of other factors
  4. Men with a higher fish intake tended to have less of an increase in blood pressure

In conclusion, results of this seven-year blood pressure follow-up study extend prior epidemiologic and short-term dietary trial data. They also lend support to the concept that blood pressure increase with age may be prevented by consuming a diet rich in fruits and vegetables and reduced in meat (except fish), in addition to other influences not studied here, such as reduced salt intake, avoidance of heavy alcohol consumption and weight control.

Reviewer Comments:
  • Large sample size
  • Dietary intake only measured at baseline and dietary data contain no information on dietary sodium, potassium, magnesium or fiber
  • No effort made to control for medication or vitamin or supplement use
  • Cutoffs (below 14 cups or 14 cups to 42 cups per month) seem arbitrary.

Research Design and Implementation 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 nutrition or dietetics practice?
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?
Yes
  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?
Yes
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?
N/A
  3.3. Were concurrent controls used? (Concurrent preferred over historical controls.)
N/A
  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 or cross-sectional 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. Criterion may not be applicable in some cross-sectional studies.)
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?
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.)
Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded?
Yes
  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?
???
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured?
No
  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?
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?
???
  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?
Yes
  7.5. Was the measurement of effect at an appropriate level of precision?
No
  7.6. Were other factors accounted for (measured) that could affect outcomes?
No
  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)?
N/A
  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
 
 

Copyright American Dietetic Association (ADA).