EAL

NA: Effect on Blood Pressure (2009)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To determine the effects of age, gender, race and weight on blood pressure from a low-salt and high-salt diet in salt-sensitive hypertensive individuals.

Inclusion Criteria:

Individuals who had valid 24-hour urine collections for sodium excretion and who showed an increase in sitting diastolic blood pressure of five mm Hg from low- to high-salt intake.

Exclusion Criteria:

People who did not meet the criteria for sodium excretion and change in diastolic blood pressure were excluded.

Description of Study Protocol:

Recruitment

Participants were recruited from a larger, multi-center, placebo-controlled, parallel group study.

Design

Randomized.

Intervention

Three weeks of ad-lib salt intake (single-blind, placebo-controlled)
Three weeks of low-salt intake (placebo-controlled)
Three weeks of high-salt intake (placebo-controlled)
Consultation with a dietitian to review a three-day food record during each diet period.

Statistical Analysis

Blood analysis performed by a central laboratory
Data analyzed with SAS version 6.10
The following were used when indicated:
- Analysis of variance
- T-tests
- F-tests
- Dunnett's test
- Fisher exact test
- Cochran-Mantel-Haenszel X² test
- Regression analysis.
A two-sided P-value of <0.05 was statistically significant.

Data Collection Summary:

Timing of Measurements

Three separate three-week periods of each diet
24-hour urine collection.

Dependent Variables

Sitting systolic blood pressure
Sitting diastolic blood pressure
Sitting mean blood pressure
Sitting heart rate
Weight
Urinary sodium.

Independent Variables

Ad-lib salt diet
Low-salt diet
High-salt diet.

Description of Actual Data Sample:

Initial N: 1,916
Attrition (final N): 624 (309 women and 315 men)
Age:
- 351 were under age 55 years
- 273 were over age 55 years.
Ethnicity:
- 367 whites
- 156 blacks
- 92 Hispanics
- Eight Asians
- One Native American.
Anthropometrics (e.g., were groups same or different on important measures):
- 195 had a body mass index of less than 27
- 429 had BMI above 27
- White subjects weighed more and consumed more ad-lib salt than black patients
- Men weighted more and consumed more ad-lib salt.
Location: Multiple sites.

Summary of Results:

Low-salt diet resulted in significant decrease in all blood pressure measurements in all ethnic groups (P<0.001)
High-salt diet resulted in significant increase in all blood pressure measurements in all ethnic groups (P<0.001)
No changes in heart rate with dietary salt changes
High correlation of blood pressure changes with 24-hour urinary sodium changes for all ages during the low-salt diet (P<0.001 for under age 55 years, P<0.047 for over age 55 years) and the high salt diet (P<0.006 for under age 55 years, P<0.001 for over age 55 years)
Both age groups showed high correlation of weight changes with salt changes
Subjects with a BMI of less than 27 had a significant decrease in all blood pressure measurements during the low-salt diet (P<0.001)
Subjects with a BMI of above 27 had a significant increase in all blood pressure measurements during the high-salt diet (P<0.001).

Author Conclusion:

There were no statistically significant effects of age, gender, race and weight on blood pressure in response to salt changes in salt-sensitive hypertensives. However, moderate salt restriction significantly lowered all blood pressure measurements in salt-sensitive hypertensives regardless of age, gender, race and weight.

Funding Source:

Reviewer Comments:

The findings of this research may be easily used in a clinical setting, emphasizing to those who are being educated that even small lifestyle changes may positively affect blood pressure.

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)	Yes

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)	Yes
	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?	N/A
	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")?	Yes
4.	Was method of handling withdrawals described?		No
	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%.)	N/A
	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?	???
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?	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?	Yes
	6.2.	In observational study, were interventions, study settings, and clinicians/provider described?	N/A
	6.3.	Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect?	Yes
	6.4.	Was the amount of exposure and, if relevant, subject/patient compliance measured?	Yes
	6.5.	Were co-interventions (e.g., ancillary treatments, other therapies) described?	Yes
	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?	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?	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)?	???
	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