HTN: Minerals (2007)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To investigate the association of calcium intake independently of other nutrients already known as predictors of hypertension.
Inclusion Criteria:
None specifically mentioned.
Exclusion Criteria:

Subjects under treatment for hypertension.

Description of Study Protocol:
  • Recruitment: Same population in Japan as used for INTERSALT study, from three districts in Japan: Osaka, Tochigi and Toyama
  • Design: Cross-sectional study
  • Intervention: 24-hour dietary recall, 24-hour urine collection and blood pressure measurements

Statistical Analysis

  • Age-adjusted means of blood pressure and mineral intake were calculated by ANCOVA
  • Adjustment was also made for age, BMI, alcohol intake and other nutrients by using multiple regression analysis
  • To adjust for drinking habits, alcohol intake was stratified into three groups.
Data Collection Summary:

Timing of Measurements

Subjects completed 24-hour dietary recall, 24-hour urinary collection and blood pressure measurements.

Dependent Variables

  • Blood pressure measurements were taken after a 30-minute period, during which smoking, eating and vigorous exercise were prohibited
  • Urine collection.

Independent Variables

  • Dietary calcium was estimated from one-day 24-hour recall, completed by dietitian interview and calculated using Japanese food table
  • Sodium and potassium intakes were evaluated by 24-hour urinary excretion.

Control Variables

  • Age
  • Alcohol intake
  • Height and weight, BMI.
Description of Actual Data Sample:
  • Initial N476 subjects; 230 men, 246 women
  • Attrition (final N): 476 subjects
  • Age: 20 to 59 years 
  • Ethnicity: Japanese
  • Anthropometrics: Statistical differences between subjects at different locations
  • Location: Japan.
Summary of Results:

 Pearson Correlation Between Variables

  SBP DBP

Calcium Intake

Men - Age  0.23, P<0.01  0.33, P<0.01  0.10

Men - BMI

 0.18, P<0.01

 0.31, P<0.01

 0.05

Men - Na excretion

 0.02

 0.03

 0.09

Men - K excretion  0.03  0.05   0.19, P<0.01
Men - Na:K ratio  0.01  -0.03  -0.06
Men - Ca intake  -0.08  -0.04  --
Women - Age  0.44, P<0.01  0.47, P<0.01  0.22, P<0.01
Women - BMI  0.31, P<0.01  0.34, P<0.01  0.00
Women - Na excretion  0.04  0.08  0.10
Women - K excretion  0.01  0.03  0.35, P<0.01
Women - Na:K ratio  0.02  0.01  -0.26, P<0.01
Women - Ca intake  -0.06  -0.06  --

Other Findings

  • Mean dietary calcium intake ranged from 557mg to 608mg per day among men and from 528mg to 639mg per day among women
  • Among men, the pooled estimates of the regression coefficients of blood pressure (mm Hg) per 100mg increase of calcium intake, adjusted for age and BMI, were -0.42mm Hg for SBP and -0.35mm Hg for DBP, but there was no statistical significance
  • Among women, the pooled estimates of the regression coefficients adjusted for age and BMI were -0.92mm Hg for SBP and -0.83mm Hg for DBP with statistical significance
  • After adjustment for age, BMI, alcohol intake and urinary excretion of sodium and potassium, the pooled estimate of calcium intake was -0.66mm Hg for DBP with statistical significance and -0.70mm Hg for SBP
  • Calcium intake correlated with urinary potassium excretion
  • We found significant negative association of calcium intake with blood pressure among women, but not men
  • A significant negative association of calcium intake with blood pressure was observed among the subjects in Osaka.
Author Conclusion:
  • Our study suggests that increased calcium intake may provide a benefit of lowering blood pressure independently with other well-known factors
  • In Japan, for prevention of osteoporosis, increasing the calcium intake, particularly among women, is one of the main issues of public health
  • This might contribute to the prevention and control of high blood pressure.
Funding Source:
Government: Ministry of Education Science and Culter of Japan
Reviewer Comments:
  • Calcium intake measured with 24-hour recall
  • Adjusted for many factors
  • Sodium and potassium excretion is a better measurement than estimated intake
  • Significant differences between subjects at different locations.
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? ???
  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? ???
  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? ???
3. Were study groups comparable? No
  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? No
  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? No
  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? ???
  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? ???
  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? 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? ???
  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? ???
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? ???
  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