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Animal Protein Products and Hypertension/Blood Pressure (DGAC)

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

To evaluate the relationship between fruit and vegetable consumption and blood pressure levels at baseline in the SUN study in order to evaluate the effect of a Mediterranean diet pattern on the risk of cardiovascular disease.

Inclusion Criteria:
None specified.
Exclusion Criteria:
  • Diagnosis of cancer
  • CHD or diabetes (eliminates reverse causation bias from diet changes due to diagnosis)
  • Diagnosis of hypertension, including those on antihypertensive medication
  • Individuals that did not report their usual blood pressure
Description of Study Protocol:

Recruitment

Ongoing recruitment in dynamic cohort study design.  Questionnaire mailed to

  • Alumni of the University of Navarra living in Spain
  • Highly educated subjects belonging to and Insurance Company (ACUNSA)
  • Registered nurses from the Professional Association of Nurses of Navarra

Design

Cross-sectional analysis of a prospective cohort.

Blinding Used (if applicable):  not applicable

Intervention

 Not specified, states detailed description published elsewhere:

  • Martínez-González MA, Sánchez-Villegas A, de Irala-Estévez J, Martí A & Martínez JA. Mediterranean diet and stroke: objectives and design of the SUN project.  Nutr Neurosci. 2002;5:65-73.
  • Sánchez-Villegas A, Delgado-Rodrígez M, Martínez-González MA & de Irala-Estévez J. Gender, age, socio-demographic and lifestyle factors associated with major dietary patterns in the Spanish project SUN (Seguimiento Universidad de Navarra).  Eur J Clin Nutr. 2003;57:285-292.
  • Designed in collaboration with Harvard Public School of Health

 Statistical Analysis

  • Food consumption adjusted for total energy intake using the residuals method.  Separated into quintiles.
  • Non-conditional logistic regression analysis to adjust for several variables at one time (prevalence odds ratios).
  • Multiple regression analysis on self-reported SBP and DBP.
    • Repeated on self-reported hypertension diagnosis or hypertension medications as a dependent variable.
  • Logistic regression analysis on stratified monounsaturated fatty acid intake.

 

Data Collection Summary:

Timing of Measurements

Subjects completed food-frequency questionnaire, baseline survey and questionnaire about blood pressure.

Dependent Variables

Blood pressure

  • Self-reported responses
    • Usual systolic (SBP) and diastolic (DBP) blood pressure
    • Systolic Categories (mm Hg): lower than 100; 101-110; 111-120; 121-130; 131-140; 141-150; 151-160; 161-175; greater than 175.
    • Diastolic Categories (mm Hg): lower than 60; 61-70; 71-80; 81-90; 91-100; 101-110; 111-120; 121-130; greater than 175
  • Participants asked if they have a medical diagnosis of hypertension
  • No specific recommendations about timing or device used to take blood pressure
  • Considered “previously undiagnosed hypertension” if
    • Subject reported no medical diagnosis of hypertension AND
    • Had a SBP =>140 mmHg AND/OR
    • Had a DBP => 90 mmHg

Independent Variables

  • Fruit, vegetable, and monounsaturated fatty acid intake
  • Dietary Assessment

    • Semi-quantitative food-frequency questionnaire
      • Validated in Spain
      • 136 individual food items
      • Standard portions specified
      • Estimated average intake over the previous year
        • Selection ranged from “never to almost never” to “more than 6 times per day”
        • 12 items for fruits
        • 11 items for vegetables

Control Variables

  • Sex
  • Age
  • Marital and employment status
  • University degree
  • Weight & height
  • Smoking status
  • Alcohol consumption
  • Physical activity
    • Metabolic equivalent index = a multiple of resting metabolic rate was assigned to each activity (MET score)
    • Time spent in each activity was multiplied by the MET score then summed over all the activities to get overall weekly MET hours.
  • Use of medication
  • Family history of CHD
  • Cancer and other diseases 
Description of Actual Data Sample:

Initial N: 8830 were first participants of the cohort, received questionnaires

Attrition (final N): 4393 remained after exclusion criteria applied

Age:  See below

Ethnicity:  not mentioned

Other relevant demographics:  see below

Anthropometrics:

Location:  Spain 

 

 

Subjects included in analysis

Participants (n)

4393

Median vegetable consumption

451.7 g/d

Median fruit consumption

262.6 g/d

Age

38.3 years

Sex

65.8 % female

BMI

23.1 kg/m2

Physical activity during leisure time in metabolic equivalents

19.8 hours/week

Energy-adjusted alcohol consumption

6.3 g/d

Energy-adjusted sodium consumption

4258 mg/d

Total fat intake

37.1 % of total energy

Monounsaturated fatty acid intake

16.0% of total energy

Saturated fatty acid intake

12.6% of total energy

Adapted from Table 1 of article

Summary of Results:
  • Age & female sex were positively correlated with fruit & vegetable consumption.
  • Alcohol & sodium intake were negatively correlated with both food groups.
  • Total fat intake inversely correlated with fruit & vegetable consumption; monounsaturated fatty acid intake did not change with vegetable consumption.
  • BMI & physical activity not related to fruit & vegetable intake.
  • Undiagnosed hypertension decreased with increasing fruit & vegetable in those with low monounsaturated fatty acid intake; relation null with high monounsaturated fatty acid intake.
  • Higher monounsaturated fatty acid intake associated with decreased undiagnosed hypertension, even with lower fruit & vegetable intake.

 Distribution by quintiles of energy-adjusted vegetable and fruit consumption

 

Q1 (lowest)

Q2

Q3

Q4

Q5 (highest)

Median vegetable consumption

240

343

452

608

957

Subjects (n)

878

879

880

878

878

Sex (% female)

49

62

65

72

79

Energy-adjusted alcohol consumption

7.3

6.0

6.9

5.8

5.3

Energy-adjusted sodium consumption

4504

4410

4555

4405

4045

Total fat intake (% of total energy)

37.7

38.0

36.9

37.1

35.5

Monounsat. Fatty acid intake (% of total energy)

15.9

16.4

16.0

16.3

15.5

Saturated fatty acid intake (% of total energy)

13.5

13.1

12.5

12.4

11.5

Median fruit consumption

114

174

263

406

726

Subjects (n)

878

879

879

879

878

Sex (% female)

54

61

65

72

76

Energy-adjusted alcohol consumption

8.3

6.5

6.3

5.7

4.5

Energy-adjusted sodium consumption

4630

4638

4426

4288

3938

Total fat intake (% of total energy)

39.3

38.6

37.7

36.2

33.5

Monounsat. Fatty acid intake (% of total energy)

16.7

16.6

16.4

15.7

14.5

Saturated fatty acid intake (% of total energy)

13.7

13.3

12.8

12.1

11.0

Adapted from table 2 & 3 of article

 

 

Q1 (lowest)

Q2

Q3

Q4

Q5 (highest)

Median vegetable consumption (g/d)

240

343

452

608

957

Participants (n)

878

879

880

878

878

Cases of undiagnosed hypertension (n)

61 (6.9%)

45  (5.1%)

45  (5.1%)

33  (3.8%)

33  (3.8%)

Median fruit consumption (g/d)

114

174

263

406

726

Participants (n)

878

879

879

879

878

Cases of undiagnosed hypertension (n)

53  (6.0%)

46  (5.2%)

41 (4.7%)

40  (4.6%)

37  (4.2%)

Author Conclusion:

A diet rich in fruits and vegetables is associated with a lower blood pressure level in a Mediterranean free-living population with an abundant intake of both fat and plant-derived foods.

 

Funding Source:
Government: Dept. of Health of the Navarre Regional Government (Spain), Spainish Ministry of Health
Reviewer Comments:
  • The methods were not published with this article
  • 50% of questionnaires analyzed after exclusion criteria applied.
  • Self-reported blood pressure
  • Authors notes study flaws such as including only individuals not previously labelled as diseased and high percentage of non-response, strengths include the relatively homogeneous population, adjusted for known HTN risk factors and increased internal validity due to highly selected population
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? ???
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 or comparisons used? (Concurrent preferred over historical control or comparison groups.) 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 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.) Yes
  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? 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? N/A
  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? 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? No
  7.5. Was the measurement of effect at an appropriate level of precision? ???
  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