HTN: Protein (2007)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To quantitatively review the data from observational studies in humans that examined the association between dietary protein intake and blood pressure.
Inclusion Criteria:

Research papers on dietary protein and BP in humans, including epidemiological cross-sectional and longitudinal studies.   

 

Exclusion Criteria:
  • Case-control studies that compared normotensive and hypertensive individuals
  • Reports published in letter or abstract form. 

 

Description of Study Protocol:
  • Recruitment: N/A  
  • Design: Computer assisted searches of English language publications on MEDLINE from January 1980 to January 2001 were conducted. References cited in related publications were also reviewed.
  • Statistical Analysis: The pooled regression coefficient (ß) and its standard error (SE) were estimated by taking the weighted average for each study of the ß and SE. If the values for ß, SE, t and units of measure for dietary protein intake were not reported, they were estimated according to a standard formula. A test of the homogeneity assumption was also performed.

 

Data Collection Summary:
  • Timing of Measurements: N/A
  • Dependent Variables: Systolic and diastolic blood pressure
  • Independent Variables: Protein intake.
Description of Actual Data Sample:
  • Initial N: 11 cross-sectional studies; two longitudinal studies
  • Attrition (final N): Nine cross-sectional studies; two longitudinal studies (N=19,954 SBP and 19,982 SBP measurements in men; 950 measurements in women) 
  • Age: Not reported
  • Ethnicity: Not reported
  • Other relevant demographics: Not reported
  • Anthropometrics: Not reported
  • Location: Not reported.

 

Summary of Results:

Pooled Regression Coefficients (ßw) of Blood Pressure on Dietary Protein Intake by Sex and Method of Dietary Assessment Used

Variables

SBP

DBP

 

No     H-Test ßw (SE)

Z-Score

P-Value No. H-Test

ßw (SE)

Z-Score

P-Value

Reported by Sex                    
Men only 19,954 p* 0.05     0.030 (0.01) 5.27 0.01 19,982 p* 0.05 0.025 (0.01) 3.78 0.01

Women only 

950 p* 0.05   0.014 (0.01)

2.28

0.022 950 p* 0.05 

0.021 (0.00)

5.37

0.01

Combined sexes 12,761 p* 0.05   0.029 (0.01) 4.01 0.01 12,508 p* 0.05  0.015 (0.00) 5.46 0.01
By methods of assessment                    
FFQ 402 N/A 0.516 (0.29) 1.79 0.072 402 N/A 0.110 (0.05) 2.20 0.02
3-day food record 61 N/A 0.133 (0.06) 2.10 0.034 28 N/A 0.168 (0.07) 2.29 0.022
24-hour diet recall 19,366 p* 0.05   0.053 (0.01) 5.84 0.01 19,348 p* 0.05  0.046 (0.01) 5.33

0.01

24-hour urine** 11,999 p* 0.05   0.025 (0.01) 3.33 0.01 11,825 p* 0.05  0.014 (0.00) 5.40 0.01

H-test": test of the homogeneity association for pooled results from more than one study
NA, not applicable (because of one study only)
Values of Z score text (see text) may be different due to rounding calculation
**Included one study on overnight urine collection (N=74)
FFQ=food frequency questionnaire.

Author Conclusion:
  • A convincing cross-sectional inverse association between dietary protein intake and BP was demonstrated by the meta-analysis of nine population-based studies
  • Evidence from the longitudinal epidemiological studies was limited and further studies will be needed to confirm this hypothesis. 
Funding Source:
Industry:
Otsuka Pharmaceutical Company
Pharmaceutical/Dietary Supplement Company:
Reviewer Comments:
  • While the number of male subjects is quite large, the number of female subjects is relatively small
  • The age and location of the subjects is unspecified, which limits the generalizability of the findings
  • Results may be potentially confounded by the different methods used to assess protein intake. 
Quality Criteria Checklist: Review Articles
Relevance Questions
  1. Will the answer if true, have a direct bearing on the health of patients? Yes
  2. Is the outcome or topic something that patients/clients/population groups would care about? Yes
  3. Is the problem addressed in the review one that is relevant to dietetics practice? Yes
  4. Will the information, if true, require a change in practice? Yes
 
Validity Questions
  1. Was the question for the review clearly focused and appropriate? Yes
  2. Was the search strategy used to locate relevant studies comprehensive? Were the databases searched and the search termsused described? Yes
  3. Were explicit methods used to select studies to include in the review? Were inclusion/exclusion criteria specified andappropriate? Wereselectionmethods unbiased? ???
  4. Was there an appraisal of the quality and validity of studies included in the review? Were appraisal methodsspecified,appropriate, andreproducible? Yes
  5. Were specific treatments/interventions/exposures described? Were treatments similar enough to be combined? ???
  6. Was the outcome of interest clearly indicated? Were other potential harms and benefits considered? ???
  7. Were processes for data abstraction, synthesis, and analysis described? Were they applied consistently acrossstudies and groups? Was thereappropriate use of qualitative and/or quantitative synthesis? Was variation in findings among studies analyzed? Were heterogeneity issued considered? If data from studies were aggregated for meta-analysis, was the procedure described? ???
  8. Are the results clearly presented in narrative and/or quantitative terms? If summary statistics are used, are levels ofsignificance and/or confidence intervals included? Yes
  9. Are conclusions supported by results with biases and limitations taken into consideration? Are limitations ofthe review identified anddiscussed? Yes
  10. Was bias due to the review's funding or sponsorship unlikely? Yes