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HTN: Protein (2007)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
  • The authors did not state a specific research objective, but protein intake in normotensive adults that attended health screening, was estimated using a single measurement of urinary nitrogen and the results correlated with systolic and diastolic blood pressure
  • After data were collected, participants were stratified into two groups based on protein intakes below 1.0g per kg per day and at least 1.0g per kg per day.
Inclusion Criteria:

None specified.

Exclusion Criteria:
None specified.
Description of Study Protocol:
  • Recruitment: No specific recruitment strategy was discussed
  • Design: Urine samples were obtained from screened (term not defined) subjects attending a one-day health check
  • Blinding used: Not discussed
  • Intervention: None.

Statistical Analysis

  • Student's T-test and Chi-square tests were used to compare the discrete variables
  • One-factor ANOVA was used to investigate the relationship between age and protein intake
  • Multivariate logistic regression analysis was used to estimate the odds ratio of the determinants of protein intake.
Data Collection Summary:

Timing of Measurements

Data were collected during a one-day health check.

Dependent Variables

  • Systolic blood pressure
  • Diastolic blood pressure.

Independent Variables

Urinary nitrogen excretion.

Control Variables

Attendence at a health screening program.
Description of Actual Data Sample:
  • Initial N: 1,299 (885 men and 414 women)
  • Attrition (final N): 1,299 (885 men and 414 women)
  • Age: Mean was 47.6 years for men, 51.0 for women
  • Ethnicity: Not specified
  • Anthropometrics: BMI (kg/m2±SD) was 24.8±3.1 for men, 23.3±3.2 for women
  • Location: Okinawa, Japan.
Summary of Results:

Variables

Protein Intake <1.0g per kg (N=615)

 

Protein Intake ≥1.0g per kg (N=684)

P-Value

Men, N (%)

359 (64.2%)

490 (71.6%)

0.0043
Age (years)                    49.7 (10.4)  47.7 (10.4) 0.0001
BMI (kg/m2) 24.8 (3.4)          23.8 (3.0) 0.0001
SBP (mmHg) 122.8 (18.2) 120.8 (17.5) NS
DBP (mmHg) 75.5 (11.4) 74.2 (11.5) NS
Total cholesterol (mg/dL) 206.8 (34.9)     204.7 (34.5) NS
BUN (mg/dL) 13.4 (3.1) 15.5 (3.4) 0.0001
Serum cr (mg/dL) 1.0 (0.2) 1.0 (0.2) NS

Hematocrit (%)

41.6 (3.7)

41.7 (3.7)

NS
Total protein (g/dL) 7.1 (0.4) 7.1 (0.3) NS
Serum albumin (g/dL) 4.3 (0.2) 4.3 (0.2) NS
Uric acid (mg/dL) 6.0 (1.4) 6.1 (1.5) NS
FBS (mg/dL) 103.0 (18.5) 103.2 (23.8) NS
HbA1c (%)     4.9 (0.7) 4.9 (.7) NS
Urine Na (mEq/day) 158 (41) 193 (45) 0.0001
Urine K (mEq/day) 50 (9) 55 (11) 0.0001
Protein intake (g/day) 54.5 (12.1) 76.5 (18.1) -
Protein intake (g/kg/day) 0.8 (0.1) 1.2 (0.2) -
Range 0.4-0.9 1.0-2.2 -

Blood Pressure and U-Na and U-K based on protein intake per unit kg body weight.

Variables

<1.0g/kg/day

≥1.0g/kg/day

P-Value

Men

 N=395

N=490

 
       SBP  (mmHg)          124.4 (17.8) 121.6 (17.4) NS
       DBP (mmHg) 77.4 (11.3) 75.2 (11.5) 0.0316
       U-Na (mEq/day) 157.6 (38.8) 195.8 (44.5) 0.0001
       U-K (mEq/day) 51.3 (9.0) 56.4 (11.1) 0.0001
Women N=220     N=194  
       SBP (mmHg) 120.0 (18.7) 118.8 (17.9) NS
       DBP (mmHg) 72.1 (10.8) 71.7 (11.0) NS

       U-Na (mEq/day)

 158.9 (43.6)

195.8 (44.5)

0.0001
       U-K (mEq/day) 46.6 (9.1) 50.9 (10.0) 0.0001

 

Author Conclusion:
  • Protein intake estimated from urinary excretion of urea was not as high as that of the Japanese national average, 82.5g per day (for those aged 40-49 years)
  • Blood pressure was lower in subjects with higher protein intake than in those with lower protein intake, despite their larger sodium intake
  • Further studies are needed to confirm the effect of protein intake on blood pressure. 
Funding Source:
Government: Ministry of Health Labor and Welfare (Japan)
Reviewer Comments:
  • Data show an inverse correlation between dietary protein intake and blood pressure. However, the authors failed to describe details of the population studied, define how they were "screened" or disclose inclusion and exclusion criteria
  • The study was conducted in Japan and there was limited comparison of the study population to the general population. Thus the ability to extrapolate these results is limited, a fact the authors acknowledged.   
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) N/A
 
Validity Questions
1. Was the research question clearly stated? No
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? No
  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? No
  2.2. Were criteria applied equally to all study groups? ???
  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) 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.) No
  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.) ???
  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.) N/A
  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? ???
  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? No
  6.6. Were extra or unplanned treatments described? No
  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? N/A
  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? ???
  7.7. Were the measurements conducted consistently across groups? ???
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? No
  10.2. Was the study free from apparent conflict of interest? Yes