EAL

NA: Dietary Factors and Effect on Sodium and Blood Pressure (2010)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To evaluate the effects of combined low-sodium (LS), high-potassium (HK), high-calcium (HCa) diet on BP in patients with mild essential hypertension.

Inclusion Criteria:

Essential hypertension
Willingness to maintain the diet
No drug therapy (N=20)
Treated with a beta blocker (N=7)
Treated with a Ca channel blocker (N=9).

Exclusion Criteria:

Secondary hypertension
Ischaemic heart disease
Congestive heart failure
Renal failure (creatinine >1.5mg/dL)
Treated diabetes mellitus.

Description of Study Protocol:

Recruitment

Patients from Hypertension Unit at Chaim Sheba Medical Center

Design

Non-randomized Crossover

Blinding used

Not applicable

Intervention

Patients divided into three groups and given diet that they followed for a month in different order
Group 1 began with LS (50mmol Na per day) diet followed by addition of HCa (supplement of 1g Ca per day) and HK (supplement of 30-60mmol K per day)
Group 2 began with HK followed by LS and HCa
Group 3 began with HCa followed by HK and LS
Third month all patients eating combined LS, HK and HCa diet.

Statistical Analysis

ANOVA
Pearson's correlation.

Data Collection Summary:

Timing of Measurements

Baseline and monthly for three months

Dependent Variables

BP: Sphygmomanometer three times in sitting position after five minutes rest
SBP/DBP: Phases 1 and 5 of Korotkoff sounds.

Independent Variables

Urine Na and K: Flame photometer
Urine Ca: Spectrophotometrically on a monarch 2000 analyzer with the indicator of methylthymol blue reagent of bioMerieux (France).

Control Variables

Dietary intake assessed by patient completing recall questionnaire under supervision of RD
Nutrient analysis using Nutritionist 3 computer program.

Description of Actual Data Sample:

Initial N: 36 patients (26 males, 12 females)
Attrition (final N): 36 patients
Age: 24-67 years (mean 46±8 years)
Ethnicity: Israeli
Other relevant demographics:
Anthropometrics:
- Energy intake: 2,260-2,600kcal per day (mean 2,424 kcal per day)
- No difference found in any of the baseline measurements in the three groups
Location: Tel Hashomer, Israel.

Summary of Results:

Nutrient Analysis

Energy intake remained unchanged (baseline value 2,424kcal per day [95% CI 2,147-2,701kcal per day] and at end 2,326kcal per day [95% CI 2,135-2,517kcal per day]
Na and K intake correlated with 24-hour urinary excretions (R=0.43 Na and R=0.4 K, P<0.001 for both)
Ca intake slightly correlated with 24-hour urinary excretion (R=0.23, P<0.01).

Low Na Diet

After one month, urinary Na excretion decreased by 25mmols per day (95% CI, 1-48 mmols per day), from 170mmols per day (95% CI, 150-190mmols per day) to 145mmols per day (95% CI, 120-170mmols per day) (P<0.05)
SBP and DBP remained unchanged
18 patients did not comply with diet
Of 18 that complied with diet, seven showed no change in SBP and were probably salt-resistant subjects. 11 showed change in SBP related to change in urinary Na excretion (R=0.64, P=0.0003)
Rate of compliance and rate of response to LS diet not affected by age, sex, BMI and waist/hip ratio.

High K Diet

After one month, urinary K excretion increased from 82mmols per day (95% CI, 71-92 mmols per day) to 87mmols per day (95% CI, 76-97mmols per day) (P=0.27)
BP unaffected and change in SBP and DBP not related to change in urinary K.

High Ca Diet

After one month, increase in Ca intake from 933mg per day (95% CI, 770-1,097mg per day) to 1,029mg per day (95% CI, 930-1,126mg per day) (P<0.05)
Urinary Ca and BP were unchanged and changes in SBP and DBP were unrelated to change in Ca intake or urinary Ca excretion.

Combined LS, HK, and HCa Diet

After three months, urinary Na excretion decreased by 34.6mmols per day (95% CI, 1.4-67.8mmols per day), (P<0.05)
Urinary Na/K ratio decreased (P<0.05)
Ca intake increased by 281mg per day (95% CI, 172-390mg per day), (P<0.01)
Urinary K and Ca remained unchanged as did body weight, SBP, DBP and mean arterial BP.

Author Conclusion:

In conclusion, dietary changes are difficult to achieve in the long run, even with intense counseling and concentrated efforts in patients willing to change life habits. Mild Na restriction is more attainable than a high K diet, but compliance decreases over time. The response to dietary intervention is heterogeneous and Na restriction may be effective only in salt-sensitive patients. Thus, only the low Na diet should be tried in patients with mild hypertension.

Funding Source:

Other:

Not given

Reviewer Comments:

Authors did not discuss bias/limitations re: non-randomization of the cross-over trial.

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?		???
	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)	No
	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.)	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?	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?	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?	N/A
	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?	???
	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.)	???
	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?	???
	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?	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?	Yes
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?	???
	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)?	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?	No
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