EAL

NA: Effect on Blood Pressure (2009)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

The researchers looked for ethnic differences in BP responsiveness to a salt challenge as related to sodium pump activity, sodium and other intracellular cations
The hypothesis was that BP responsiveness is related to sodium and calcium in both African-American and white individuals with normal and high blood pressure.

Inclusion Criteria:

Women who were healthy, post-menopausal and within 30% of ideal body weight.

Exclusion Criteria:

Patients were excluded or discontinued for a systolic BP (SBP) 200mm Hg or a diastolic BP (DBP) 115mm Hg at any visit, SBP 180 or DBP 110 on any two visits, symptomatic hypertension, clinical evidence of secondary hypertension or history of excess alcohol or recreational drug use.

Description of Study Protocol:

Recruitment: Post-menopausal women with similar distribution of hypertensives, normotensives, whites and African-Americans
Design: Two-period crossover using a high-salt diet (more than 200mEq per day) and a low-salt diet (less than 20mEq per day) in random order
Intervention: Each participant was randomized to receive seven days of either a low-salt or a high-salt diet initially. Another diet was prescribed during a second seven-day period.
Statistical Analysis: SPSS software
- The two groups were compared using two-tailed Student T-test or Wilcoxon signed-rank test for normally distributed data
- P<0.05 considered significant
- For comparing more than one group, the researchers used ANOVA with adjustment for multiple comparisons.

Data Collection Summary:

Timing of Measurements

One seven-day diet period of either high-salt or low-salt diet in random order
Second seven-day period with the alternative diet that was not used during the initial week
After an overnight stay, supine blood pressure and heart rates were measured every 15 minutes over a four-hour period.

Dependent Variables

Blood pressure
Heart rate
Measured using DinaMap vital signs monitor.

Independent Variables

Diet with varied salt content.

Description of Actual Data Sample:

Initial N: 199 females
Attrition (final N): 199
Mean age: 56
Ethnicity: White and African-American individuals
Other relevant demographics: Post-menopausal women
Anthropometrics:
- Similar in education
- Family history of hypertension
- Socioeconomic status
- Blood pressure
- Renal function
- Use of estrogen replacement.
Location: Cleveland, Ohio.

Summary of Results:

More than half of the subjects in both ethnic groups were salt-sensitive
Salt resistance was similar in both ethnic groups
The mean blood pressure increase after a high-salt diet was significantly greater in African-Americans
Systolic blood pressure increased 18.3+12.7mm Hg in African-Americans and 13.7+12.2mmHg in whites (P<0.01).
Elevated sodium and calcium were associated with salt responsiveness in African-Americans, not in whites
Salt-sensitive and salt-intermediate African-Americans had higher sodium than the corresponding whites
Calcium was significantly higher in salt-sensitive African-Americans
Calcium and sodium did not differ significantly in the salt-resistant groups
The low-salt diet resulted in no difference in cation levels based on ethnicity and salt responsiveness
Salt-sensitive African-Americans had significantly higher ratios of sodium, potassium, calcium and magnesium than whites when on the high-salt diet
Salt-sensitive African-Americans had a significantly (P=0.30) lower maximal sodium pump activity.

Author Conclusion:

The study confirms a possible link between calcium and salt sensitivity because there was increased calcium in salt-sensitive and salt-intermediate African-American women. These differences were not found in salt-resistant subjects. There was a high prevalence of salt sensitivity in both African-Americans and whites (54% and 51%, respectively). Salt-sensitive and salt-intermediate African-Americans had a significantly higher sodium and sodium-potassium ratio than did the corresponding white groups. The ratio of calcium to magnesium was significantly higher in salt-sensitive African-Americans compared with salt-sensitive whites when on a high-salt diet.

Funding Source:

Reviewer Comments:

In salt-sensitive African-Americans, there appears to be a positive association between cations and ratios of intracellular sodium to potassium and intracellular calcium to magnesium.

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)	N/A
	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")?	N/A
4.	Was method of handling withdrawals described?		No
	4.1.	Were follow-up methods described and the same for all groups?	No
	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%.)	No
	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?		No
	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?	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?	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?	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)?	No
	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