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HTN: Sodium (2015)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To examine the relation between blood pressure and urinary sodium as a marker of dietary intake in men and women living in the general population.
Inclusion Criteria:
  • Adults aged 45 to 79
  • None specifically mentioned.
Exclusion Criteria:
None specifically mentioned.
Description of Study Protocol:
  • Recruitment: EPIC-Norfolk (European Prospective Investigation into Cancer in Norfolk): A prospective population study of approximately 25,000 men and women unselectively recruited from general practice age-sex registers, who participated in a baseline survey
  • Design: Cohort study
  • Intervention: Questionnaire and health exam.

Statistical Analysis

  • Differences were tested by using ANOVA
  • Significance values are shown for the trend test
  • In persons with no history of HTN, the percentage of those with newly diagnosed HTN were examined
  • The percentage of those with optimal blood pressure was also examined
  • The regression of blood pressure on urinary sodium-creatinine as a continuous variable, adjusted for age, BMI, smoking and urinary potassium-creatinine was estimated.
Data Collection Summary:

Timing of Measurements

Participants completed a detailed health and lifestyle questionnaire at the baseline survey between 1993 and 1997 and attended a clinic for a health examination.

Dependent Variables

Blood pressure measured by an Accutorr non-invasive oscillometric blood pressure monitor.

Independent Variables

  • Sodium, potassium and creatinine concentrations were assayed in urine samples
  • Dietary sodium also analyzed through seven-day food records for about 7,000 participants.

Control Variables

  • BMI
  • Age
  • Cigarette smoking
  • Urinary potassium-creatinine.
Description of Actual Data Sample:
  • Initial N: 23,104 community-living adults
  • Attrition (final N): 23,104 adults, 10,812 men, 12,922 women
  • Age: 45 to 79 years 
  • Ethnicity: Not mentioned
  • Anthropometrics: The cohort was comparable to the national population, with respect to anthropometric indices, blood pressure and lipids, but had a lower prevalence of smokers.
  • Location: United Kingdom.

 

Summary of Results:

 By Categories of Urinary Sodium-Creatinine (mmol-mmol)

Men Less than 7.1 7.1 to 10.3 10.4 to 14.0 14.1 to 19.5 Over 19.5 P for Trend
N 2,229 2,470 2,382 2,123 1,590  

Na:creatinine

 4.9±1.5 8.7±1.0 12.2±1.1

16.4±1.5

25.5±5.8

 

K:creatinine

 5.6±2.3 6.4±2.5 7.0±2.7

7.8±2.9

9.2±4.0

<0.0001
Na:K 1.0±0.5 1.6±0.6 2.0±0.8 2.4±0.9 3.1±1.2 <0.0001
Age (y) 60.4±8.9 59.4±8.8 59.3±8.8 59.5±8.8 60.5±8.8 <0.0001
BMI 26.5±3.3 26.6±3.3 26.5±3.2 26.6±3.2 26.5±3.4  0.57
SBP (mm Hg) 136.7±17.9 136.3±16.8 136.9±16.6 138.9±17.7 142.1±18.9 <0.0001
DBP (mm Hg) 83.2±11.4 83.8±10.9 84.2±10.8 85.3±11.1 86.6±11.4 <0.0001

 

Women Under 7.1 7.1 to 10.3 10.4 to 14.0 14.1 to 19.5 Over 19.5 P for Trend
N 2,509 2,270 2,351 2,623 3,149  

Na:creatinine

 4.6±1.7 8.8±1.0 12.2±1.1

16.5±1.6

27.1±6.8

 

K:creatinine

 7.0±3.2 8.0±3.5 9.0±4.0

9.9±4.1

12.3±5.1

<0.0001
Na:K 0.8±0.4 1.3±0.6 1.6±0.7 2.0±0.9 2.5±1.2 <0.0001
Age (y) 59.8±9.0 58.3±8.8 58.7±8.7 58.7±8.7 59.5±8.8 <0.0001
BMI 26.4±4.5 26.1±4.2 26.3±4.3 26.2±4.3 26.2±4.1 0.13
SBP (mm Hg) 132.4±18.5 132.5±18.4 133.5±18.0 134.3±18.4 137.9±19.7 <0.0001
DBP (mm Hg) 80.3±11.1 80.1±11.0 80.7±10.7 81.3±10.9 82.8±11.4 <0.0001

Other Findings

  • Mean SBP and DBP increased as the ratio of urinary sodium to creatinine increased (as estimated from a casual urine sample), with differences of 7.2mmHg for SBP and 3.0mmHg for DBP (P<0.0001) between the top and bottom quintiles
  • This trend was independent of age, BMI, urinary potassium:creatinine and smoking and was consistent by sex and history of hypertension
  • The prevalence of those with SBP over 160mmHg halved from 12% in the top quintile to 6% in the bottom quintile. The odds ratio for having SBP over 160mmHg was 2.48 (95% CI, 1.90, 3.22) for men and 2.67 (95% CI, 2.08, 3.43) for women in the top, compared with the bottom quintile of urinary sodium.
  • Estimated mean sodium intakes in the lowest and highest quintiles were about 80mmol and 220mmol per day, respectively.
Author Conclusion:
  • Within the range found in a free-living population, even modest and entirely feasible differences in sodium intake are associated with blood pressure differences of clinical and public health relevance
  • Our findings reinforce current recommendations to lower sodium intake in the general population.
Funding Source:
Government: Medical Research Council (UK), EU
Not-for-profit
0
Foundation associated with industry:
Reviewer Comments:
  • Inclusion and exclusion criteria and recruitment methods not well-defined
  • Did not look at other possible factors such as medication.
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) 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? ???
  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? No
  2.2. Were criteria applied equally to all study groups? ???
  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) 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? Yes
  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? 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? 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? 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? ???
  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? ???
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? ???
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