HTN: Sodium (2015)

Citation:
 
Study Design:
Class:
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Quality Rating:
Research Purpose:
To examine the associations of dietary sodium and potassium, as reflected by the urinary sodium-potassium excretion and calcium intake with blood pressure and the prevalence of hypertension among older Chinese vegetarians in Hong Kong.
Inclusion Criteria:
  • Vegetarians over the age of 55 years
  • Vegetarians for at least 10 years due to religious beliefs.
Exclusion Criteria:
Subjects with a mental score of less than eight out of 12 to ensure reliability of dietary intake data.
Description of Study Protocol:
  • Recruitment: Subjects recruited from members of religious organizations or old age hostels
  • Design: Cross-sectional study
  • Intervention: 24-hour recall, blood pressure measurements, blood samples, ECG.

Statistical Analysis

  • The bivariate correlations between blood pressures, dietary intake variables and other predictors (age, diabetes mellitus, serum creatinine, albumin and vitamin B12, old age residence, years of vegetarian diet and BMI) were examined for statistical significance
  • Those variables with P-values of less than 0.05 were entered into a stepwise regression analysis model for SBP and DBP.
Data Collection Summary:

Timing of Measurements

24-hour recall, blood pressure measurements, blood samples, ECG.

Dependent Variables

  • Prevalence of hypertension, defined as supine blood pressure above 140/90mm Hg or a history of hypertension
  • Blood pressure using standard mercury sphygmomanometer
  • Fasting blood samples for glucose, albumin, creatinine, vitamin B12, folate
  • Resting ECG.

Independent Variables

  • Dietary sodium, potassium, calcium, protein and dietary fiber intakes assessed by 24-hour recall method or fasting urinary sodium or potassium-creatinine ratios
  • Mental status assessed by information and orientation, part of the Clifton assessment procedure of the elderly to ensure reliability of dietary recall data
  • Use of calcium and vitamin supplements was noted.

Control Variables

  • Past medical history
  • Concurrent drug treatment
  • Alcohol intake. 
Description of Actual Data Sample:
  • Initial N111 ambulatory vegetarians, all women
  • Attrition (final N): 71 hypertensive, 40 normotensive women. Data on dietary intake only available for 86 subjects, due to subnormal mental test scores, reluctance to participate or loss of original data.

Age

  • Hypertensive: 78.7±6.9 years
  • Normotensive: 76.7±7.9 years.

Ethnicity

Chinese.

Other Relevant Demographics
  • 29 (26%) had history of HTN
  • 22 on drug treatment
  • 42 (38%) had blood pressure over 140/90.

Anthropometrics

Hypertensive and normotensive subjects had statistically significant differences for duration of vegetarianism, SBP, DBP and ischaemic ECG.

Location

Hong Kong.

Summary of Results:

 

  Hypertensive Normotensive P-Value
Na/Creatinine Ratio 32.6±19.3 21±12.4 0

K/Creatinine Ratio

7.7±3.8

6.9±3.1

NS

Na/K Ratio 4.7±2.8 3.4±2.3 0.02
Energy (kcal) 1181±348 1225±397 NS
Protein (g) 33.1±14.0 38.4±20.9 NS
Calcium (g) 411±324 589±428 0.04
Potassium (mg) 1160±606 1131±661 NS
Vitamin C (mg) 128±81 136±65 NS
Thiamin (mg) 0.48±0.30 0.50±0.31 NS
Fiber (g) 9.2±6.8 9.2±5.9 NS
Serum Vitamin B12 (pmol/L) 205±196 244±323 NS
Serum folate (umol/L) 47.5±9.83 45.6±11.1 NS

Serum albumin (g/L)

37.5±2.9

37±2.4

NS

 

Other Findings

  • 71 subjects (64%) were found to have hypertension.
  • Compared with normotensive subjects, hypertensive subjects had lower calcium intake (411±324 vs. 589±428mg, P=0.04), but higher urinary sodium-creatinine ratio (32.6±19.3 vs. 21.0±12.4, P=0.00) and urinary sodium-potassium ratio (4.7±2.8 vs. 3.4±2.3, P=0.02)
  • Among 88 subjects not taking diuretics or antihypertensive drugs, SBP was related to calcium intake (R=-0.40), urinary sodium-creatinine ratio (R=0.39), urinary sodium-potassium ratio (R=0.30) and age (R=0.23)
  • DBP was related to urinary sodium-creatinine (R=0.29). Urinary potassium-creatinine did not significantly correlate with either SBP or DBP (P=0.82, 0.36 respectively)
  • 23 subjects with high urinary sodium-potassium and low calcium intake and 16 subjects with low urinary sodium-potassium ratio and high calcium intake differed markedly, with respect to SBP (159±26 vs. 130±15mm Hg) and prevalence of hypertension (78% vs. 25%).
Author Conclusion:
  • We concluded that in contrast to the Western vegetarian diets, features of the Chinese vegetarian diet, high sodium and low calcium intakes, might pre-dispose to hypertension
  • As the combination of dietary intakes is common in Asian countries, public health interventions against this dietary pattern may have major impact on the incidence and prevalence of hypertension in this most populous part of the world.
Funding Source:
University/Hospital: Chinese University of Hong Kong
Reviewer Comments:

Recall data reliable due to mental assessment.

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? 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.) 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? 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? 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? 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