NA: Sodium or Sodium Chloride (2010)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To assess the relationship of urinary excretions of sodium and potassium and their ratio with subsequent cardiovascular disease (CVD) (stroke, myocardial infarction, coronary revascularization or CVD mortality).

Inclusion Criteria:
  • Participated in the Trials of Hypertension Prevention Study
  • Not assigned to an active sodium reduction intervention in the previous Trials of Hypertension Prevention Study
  • Follow-up information obtained.
Exclusion Criteria:
  • Former study participants without follow-up information
  • Former study participants who died
  • Former participants who were assigned to an active sodium reduction intervention.
Description of Study Protocol:

Recruitment

Through contact information from previous study.

Design

An observational analysis of the relationship of usual sodium and potassium intake ascertained during the trial periods with subsequent CVD or mortality end points.

Statistical Analysis

  • Mean urinary excretion levels were examined across categories of baseline characteristics and were tested using linear regression analysis
  • Because of large differences between sex, sex-specific quartile categories of urinary sodium and potassium excretion and their ratio were performed
  • Ratio rate for quartile categories of urinary excretion from the end of the trial period to the end of the follow-up period
  • Sodium to potassium excretion ratio was examined by comparing standardized coefficients for sodium, potassium and the ration and by assessing model fit using the Bayes information criterion
  • Within person variability corrected using multivariate regression calibration.

 

Data Collection Summary:

Dependent Variables

CVD risk.

Independent Variables

Urinary excretion of sodium and potassium data.

 


 

 

Description of Actual Data Sample:
  •  Initial N: 2,275 (males 1,601, females 705). This is 76.5% of the original sample.
  • Attrition (final N): 2,275
  • Age: 30 to 54 years
  • Ethnicity: White, 1,922; black, 322; other, 62.

Anthropometrics

  • BMI 30 or more: 586 males, 288 females
  • BMI 25 to 30: 777 males, 279 females
  • BMI less than 25: 238 males, 138 females
  • No change in weight: 641 males, 276 females.

Other Relevant Demographics

  • Current smokers = 238
  • Family history of cardiovascular disease
    • Yes: 203
    • No: 2,093
  • 193 CVD events.

Location

Boston, Massachusetts.

 

Summary of Results:

 

  • Overall median urinary Na excretion was 158mmol per 24 hours (IQR=127 to 194mmol per 24 hours); this was higher among males (171mmol per 24 hours) compared to females (134mmol per 24 hours). Median urinary K excretion was 60mmol per 24 hours (IQR=48 to 73mmol per 24 hours); median Na:K excretion 2.8mmol per 24 hours (IQR=2.2 to 3.4mmol per 24 hours). 
  • After adjusting for baseline variables and lifestyle changes, there was a non-significant trend in CVD risk across sex-specific quartiles of urinary Na excretion (RR 1.00, 0.99, 1.16, and 1.20, respectively; P=0.38 for trend) and K excretion (RR 1.00, 0.94, 0.91, 0.64; P=0.08 for trend). A significant trend for Na:K excretion was found (RR 1.00, 0.84, 1.18, 1.50; P=0.04 for trend). When including both Na and K in the model: RR 1.42; 95% CI 0.99 to 2.04 out of 100mmol per 24 hours of urinary Na excretion (P=0.05) and RR=0.67; 95% CI 0.41 to 1.10 out of 50mmol per 24 hours of urinary K excretion (P=0.12). A model including Na:K excretion: RR=1.24, 95% CI 1.05 to 1.46 (P=0.01) had the best fit.   
  • Suggested positive relationship of urinary sodium excretion and a suggested inverse relationship of urinary potassium excretion with risk of CVD, but neither was statistically significant when considered separately. Both measures strengthened when modeled jointly, with opposite but similar effects on risk. The sodium to potassium excretion ratio displayed the strongest and statistically significant association with a 24% increase in risk per unit of the ratio that was similar for CHD and stroke and was consistent across subgroups. 


 

Author Conclusion:

Reduced CVD risk among subjects with lower sodium intake, higher potassium intake or both. Lowering dietary sodium intake, while increasing potassium consumption, at the population level might reduce the incidence of CVD.

Funding Source:
University/Hospital: Brigham and Woman's Hospital
Reviewer Comments:

Detailed discussion of limitations of previous research studies.

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? N/A
  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? N/A
  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.) 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? N/A
  4.1. Were follow-up methods described and the same for all groups? N/A
  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? 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? N/A
  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? 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? 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? N/A
  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? 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? 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