HTN: Potassium (2015)
Citation:
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To investigate whether salt might be an important contributory factor for hypertension in Hong Kong Chinese patients with untreated hypertension.
Inclusion Criteria:
- Age between 18 and 75 years
- Essential hypertension newly diagnosed or previously diagnosed, according to WHO/International Society of Hypertension criteria, but not treated with medications.
Exclusion Criteria:
- Significant cardiac disease, including valvular heart disease, arrhythmia, previous myocardial infarction, angina and heart failure
- Known or suspected renal or renovascular disease
- Liver disease
- Edema
- Pregnancy
- Any serious concomitant disease
- Patients who were on a special diet.
Description of Study Protocol:
- Recruitment: Patients were referred to the hypertension outpatient clinic of a university teaching hospital
- Design: Case-control study
- Intervention: Subjects underwent several measurements, in addition to blood pressure measurements and urine collection.
Statistical Analysis
- Spearman's rank correlation was used as normal distribution of data was not assumed
- Stepwise multiple regression was used to investigate the relationship between DBP and independent variables
- Logarithmic transformation of the 24-hour urinary sodium excretion resulted in slightly higher R2 values and did not affect the conclusions.
Data Collection Summary:
Timing of Measurements
- Full medical histories, physical exams, blood tests, electrocardiogram and posteroanterior chest X-ray were completed
- Blood pressure measurements and 24-hour urine collection performed for each patient and repeated 12 weeks later in 14 hypertensive patients who remained untreated
- 22 hypertensive patients underwent ambulatory blood pressure monitoring.
Dependent Variables
Blood pressure measured with strict protocol under standardized conditions in a temperature-controlled environment, with the mean of three readings used for analysis.Independent Variables
Dietary intake of sodium measured through urine excretion.Control Variables
- Age
- Gender
- BMI
- Ethanol intake
- Season.
Description of Actual Data Sample:
- Initial N: 117 subjects
- 47 normotensive controls (21 male, 26 female)
- 70 untreated hypertensives (43 male, 27 female).
- Attrition (final N): See above
- Age: Hypertensive patients mean, 46±14 years; controls mean, 41±12 years
- Ethnicity: Not mentioned
- Location: Hong Kong, China.
Summary of Results:
Urinary Sodium Excretion | P-Value | Diastolic Blood Pressure | P-Value | |
DBP | R=0.41 | <0.001 | ||
Ambulatory DBP |
R=0.47 |
0.026 |
R=0.55 |
0.008 |
Repeat DBP |
R=0.60 |
0.02 |
R=0.68 |
0.01 |
SBP | R=-0.01 | NS | R=0.28 | 0.02 |
Age | R=-0.09 | NS | R=-0.16 | NS |
Gender | R=-0.08 | NS | R=-0.21 | NS |
BMI | R=0.16 | NS | R=0.33 | 0.007 |
Urinary Potassium Excretion | R=0.13 | NS | R=-0.24 | 0.05 |
Other Findings
- In the hypertensive patients, DBP correlated with 24-hour urinary sodium excretion (R=0.41, P<0.001), even after adjustment for age, gender, BMI, ethanol intake and season (R=0.34, P=0.02)
- In normotensive controls, DBP did not correlate with sodium excretion (R=0.21, P=0.16)
- A correlation between DBP and sodium excretion was also observed in the patients who underwent ambulatory blood pressure monitoring (R=0.47, P=0.026) and in repeat measurements in untreated patients (R=0.60, P=0.02)
- SBP did not correlate with sodium excretion, although it increased with patient age (0.6±0.1mm Hg per year, P<0.001)
- In a multiple regression analysis with DBP as the dependent variable, the regression coefficient was 0.06±0.02mm Hg per mmol sodium
- The regression coefficients for ambulatory DBP and diastolic pressure repeated at 12 weeks were 0.07±0.03 and 0.09±0.04mm Hg per mmol sodium, respectively.
Author Conclusion:
- In conclusion, our results show that sodium intake is strongly related to diastolic blood pressure in our hypertensive patients, accounting for 17% of the variance of diastolic blood pressure
- Long-term reduction in salt intake may be indicated, at least in these hypertensive patients, if not the whole population.
Funding Source:
University/Hospital: | Ninewells Hospital and Medical School |
Reviewer Comments:
Controlled for many variables.
Quality Criteria Checklist: Primary Research
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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) | N/A | |
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? | 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.) | Yes | |
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.) | 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? | 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? | Yes | |
6.6. | Were extra or unplanned treatments described? | Yes | |
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)? | N/A | |
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 | |