NA: Sodium or Sodium Chloride (2010)

Study Design:
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Quality Rating:
Research Purpose:

To determine the mean dietary salt intake in urban south India and to look at its association with hypertension.

Inclusion Criteria:

Every tenth subject in a sample of 26,001 individuals 20 years of age and over of Chennai City in southern India.

Exclusion Criteria:

Subjects with a self-reported history of diabetes, cardiovascular disease and hypertension.

Description of Study Protocol:
  • Recruitment: Every tenth subject of the 26,001 subjects in a representative sample of individuals in Chennai City in southern India
  • Design: Cohort
  • Statistical Analysis:
    • Statistical software package SPSS (10.0 version; SPSS inc., Chicago, Illinois)
    • One-way ANOVA
    • Chi-squared test
    • Multiple logistic regression analysis.
Data Collection Summary:

Timing of Measurements

  • On entering study subjects underwent OGTT
  • Anthropometric measurements of weight, height, waist and hip measurements
  • Demographic, socioeconomic characteristics, medical history, medications, family history of diseases, smoking and alcohol consumption also obtained. 

 Dependent Variables

  • BP measured in right upper limb in sitting position to nearest two mm Hg using a Hg sphygmomanometer (Diamond Deluxe BP apparatus, Industrial Electronic and Allied Products, Pune, India). Two readings taken five minutes apart and averaged.
  • Hypertension diagnosed if BP greater than or equal to 130/85mm Hg based on NCEP Adult Treatment Panel III criteria. 

Independent Variables

Salt intake and other nutrients assessed using a validated semi-quantitative FFQ which contained 222 food items designed to estimate food intakes during the preceding year.


Description of Actual Data Sample:
  • Initial N: 2,600
  • Attrition (final N): 1,902 (821 males and 1,081 females)
  • Age: over 20 years old
  • Ethnicity: Indian
  • Other relevant demographics: Anthropometrics
    • Hypertensive subjects were older (44.9±12.9 years) vs. normotensive (36.7±11.2 years) (P<0.0001)
    • Hypertensive subjects had higher BMI (25.0±4.8kg/m2) vs. normotensive (23.4±4.4kg/m2) (P<0.001)
    • Hypertensive subjects had higher waist circumference (88.2±11.2cm) vs. normotensive (81.8±11.6cm) (P<0.0001)
    • Hypertensive subjects had higher mean daily salt intakes (9.9g) vs. normotensive (8.0g) (P<0.0001)
    • Hypertensive subjects had higher dietary sodium intakes (4,357±1,570mg) vs. normotensive (3,607±1,209mg) (P<0.0001)
    • Mean daily salt intake in the total sample was 8.5 grams per day which was higher than the five grams per day recommended by WHO
  • Location: Chennai City (formerly Madras) in southern India.
Summary of Results:

 Salt Intake

  • Intake of dietary salt ranged from 4.9 grams per day in the lowest quintile to 13.8 grams per day in the highest quintile
  • Higher intake of dietary salt associated with older age (Q1=37.6±12.9 years, Q5=41.7±13.4 years, P=0.037) 
  • Higher intake of dietary salt associated with higher BMI (Q1=22.1±3.9kg/m2, Q5=24.8±4.4kg/m2P<0.0001)
  • Higher intake of dietary salt associated with higher waist circumference (Q1=79.3±10.8cm, Q5=87.0±11.0cmP<0.0001)
  • Higher intake of dietary salt associated with higher SBP (Q1=113.0±13.3mm Hg, Q5=129.2±23.0mm HgP<0.0001)
  • Higher intake of dietary salt associated with higher DBP (Q1=70.5±10.1mm Hg, Q5=78.3±12.6 years, P<0.0001) 
  • Prevalence of hypertension increased with increasing quintiles of salt intake (Q1=16.6% vs. Q5=48.4%; Chi-square trend =95.4; P<0.0001)
  • Daily calorie intake increased across quintiles of salt intake (Q1=2,077±519kcal, Q5=2,842±760kcal, P<0.0001)
  • Daily percentage of calories from fat increased across quintiles of salt intake (Q1=21.9±4.7%, Q5=25.1±5.7%, P<0.0001)
  • Mean salt intake at age group 20 years to 29 years was 8.1 grams per day and 9.6 grams per day for those over 60 years of age (P=0.003)
  • Intake of dietary salt higher in those with household incomes above Rs 10,000 per month (9.4g, P=0.006) compared with those with less than Rs 2,000 per month (7.9g, P=0.006)
  • Prevalence of hypertension higher among subjects who added more than one tablespoon per day of extra salt to their foods at the table compared to those who did not add any extra salt (38.5% vs. 23.3%; Chi-square=18.95, P<0.0001).

Dietary Salt and BP among Normotensives

  • SBP increased with increasing quintiles of salt intake (Q1=108.8mm Hg, Q5=111.9mm HgP<0.0001)
  • DBP increased with increasing quintiles of salt intake (Q1=67.7mm Hg, Q5=70.3mm HgP<0.0001)
  • SBP showed a strong correlation with dietary salt intake (R=0.349, P<0.0001) and dietary Na (R=0.324, P<0.0001)
  • DBP showed a strong correlation with dietary salt intake (R=0.263, P<0.0001) and dietary Na (R=0.251, P<0.0001).

Association of Dietary Salt with Hypertension

  • In unadjusted multivariate logistic regression analysis, total dietary salt intake showed 1.190 (95% CI: 1.153-1.228, P<0.0001) times higher risk for hypertension
  • After adjusting for confounding variables, dietary salt intake was still associated with hypertension (OR: 1.161, 95% CI: 1.115-1.209, P<0.0001)
  • In unadjusted model, salt added at table above one tablespoon per day showed two-fold higher risk for hypertension (OR: 2.059, 95% CI: 1.488-2.849, P<0.0001) compared to zero added salt taken as the reference
  • After adjusting for known risk factors such as age, sex and BMI, association between added salt intake (tablespoon per day) and hypertension remained (OR: 1.759, 95% CI: 1.240-2.495, P=0.002)  
  • Further adjustment for dietary variables such as total energy and dietary fat did not substantially change this association (OR: 1.698, 95% CI: 1.176-2.452, P=0.005).


Author Conclusion:

Intake of dietary salt in urban south India is higher than currently recommended. Increasing salt intake is associated with increased risk for hypertension even after adjusting for potential confounders. This calls for urgent steps to decrease consumption of the population at high risk.

Funding Source:
Reviewer Comments:
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) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? ???
  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.) 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? No
  4.4. Were reasons for withdrawals similar across groups? ???
  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? ???
  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.) ???
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? ???
  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? N/A
  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? N/A
  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? 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? N/A
  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? N/A
  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? Yes
  10.2. Was the study free from apparent conflict of interest? Yes