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HTN: Calcium (2015)

Citation:

Hilpert KF, West SG, Bagshaw DM, Fishell V, Barnhart L, Lefevre M, Most MM, Zemel MB, Chow M, Hinderliter AL, Kris-Etherton PM. Effects of dairy products on intracellular calcium and blood pressure in adults with essential hypertension. J Am Coll Nutr. 2009; 28(2): 142-149.

PubMed ID: 19828899
 
Study Design:
Randomized Crossover Trial
Class:
A - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
To clarify the effect of dairy foods as part of a DASH-type diet on blood pressure, intracellular ions and calcium-regulating hormones in individuals with Stage 1 hypertension.
Inclusion Criteria:
Adults with Stage 1 hypertension (systolic BP between 140mm Hg to 159mm Hg and diastolic BP between 90mm Hg to 99mm Hg).
Exclusion Criteria:
  • BMI higher than 35kg/m2
  • Smoking
  • History of:
    • Congestive heart failure
    • Peripheral artery disease
    • Myocardial infarction
    • Stroke
    • Angina
    • Intermittent claudication
    • Kidney stones
    • Renal disease.
  • Allergies to:
    • Food
    • Latex
    • Nitroglycerin.
  • Presence of any disease known to affect calcium balance
  • Use of nutritional supplements, hormone replacement therapy or any drug known to alter calcium balance, BP or cholesterol metabolism.
Description of Study Protocol:

Recruitment

Recruitment methods were not reported.

Design

A randomized, three-period crossover controlled feeding study was conducted at two sites. Participants were fed three experimental diets for five weeks each. Endpoints were assessed at the end of each diet period and a two-week compliance break separated diets.

Blinding Used

Implied with measurements.

Intervention

  • Participants were fed the following three experimental diets for five weeks each:
    • AWD (control): An average Western diet containing 0.4 servings per day of full-fat dairy products
    • F&V: A diet high in fruits and vegetables containing 0.4 servings per day of lower-fat dairy products
    • D-F&V: A diet high in fruits and vegetables containing 3.4 servings per day of dairy products (low-fat and non-fat milk and yogurt and full-fat cheese).
  • The F&V and D-F&V diets were matched for macronutrients, cholesterol and fiber, and included the same fruits and vegetables in similar proportions. The F&V and AWD diets were matched for calcium and did not exceed 600mg per day at the highest kcal level. Sodium was matched across all three diets.
  • Food was prepared in research kitchens according to study protocol. On weekdays, subjects ate one meal in the feeding center; body weight was recorded. Other meals and snacks were packaged for takeout. Diet compliance was monitored according to procedures used in research centers. Subjects were instructed to maintain their usual lifestyle and exercise habits, to consume all foods provided, to abstain from consuming other foods and to limit beverages containing caffeine (less than five servings per day) and alcohol (less than two servings per week). Weight was maintained by adjusting calories. 

Statistical Analysis

  • The mixed procedure (PROC MIXED) was used to test for effects of diet, diet order, diet period and their interactive effects on each outcome variable
  • All models were adjusted for study site and age; models for BP change were also adjusted for screening values
  • A Tukey’s least-significant different test was performed when significant diet effects were detected to determine the source of significant main effects or interactions (P≤0.05)
  • Within-subject correlation analyses were used to test associations between RBC calcium and BP.
  • Data are presented as least squares means ±SE.
Data Collection Summary:

Timing of Measurements

Endpoints were assessed at the end of each five-week diet period.

Dependent Variables

  • Blood pressure
  • Intact parathyroid hormone (iPTH)
  • Serum calcium
  • 1,25-dihydroxyvitamin D
  • Calcitonin
  • Renin activity
  • Red blood cell ions:
    • Calcium
    • Magnesium
    • Sodium
    • Potassium.
  • Urinary electrolytes:
    • Calcium
    • Sodium
    • Potassium.

Independent Variables

Participants were fed the following three experimental diets for five weeks each:

  • AWD (control): An average Western diet
  • F&V: A diet high in fruits and vegetables
  • D-F&V: A diet high in fruits and vegetables containing 3.4 servings per day of dairy products.

Control Variables

  • Study site
  • Age
  • BP screening levels.
     
Description of Actual Data Sample:
  • Initial N: A total of 23 (16 male, seven female)
  • Attrition (final N): A total of 23 (20 completed all three diet periods; three completed two diet periods)
  • Age: Ranged from 22 to 70 years
  • Ethnicity: All participants were Caucasian.

Anthropometrics

  • All participants had normal or moderately elevated cholesterol (LDL lower than 4.91mmol per L; HDL in the 15th to 95th percentile of NHANES III and triacyglycerols less than 3.95mmol per L)
  • Subjects served as own control in crossover design.

Location:

  • Pennsylvania State University, Pennsylvania
  • Pennington Biomedical Research Center, Louisiana.
Summary of Results:

Key Findings

  • All three diets significantly decreased SBP and DBP (P≤0.01 for all). The reductions in SBP and DBP following the F&V and D-F&V diets were significantly greater (approximately 2mm Hg) compared with AWD (P<0.05). The changes in SBP and DBP did not differ between the two intervention diets.
Mean Changes in BP
 
  SBP DBP
AWD -9.9±1.5 -5.3±1.2
F&V -12.3±1.5 -7.2±1.2
D-F&V -12.0±1.5 -7.0±1.2
  • 1,25-dihydroxyvitamin D was significantly lower after the D-F&V diet (P<0.01) vs. the F&V and AWD diets (87.4±7.0, 104.0±7.0, 112.2±7.0, respectively)
  • The concentration of RBC calcium was significantly lower after the D-F&V diet (P=0.0001) vs. both the F&V and AWD diets (6.9±1.1, 12.1±1.1, 12.6±1.0, respectively)
  • Subjects who responded to the D-F&V diet by significantly reducing intracellular calcium [(Ca)i] exhibited significantly greater net decreases in DBP on the D-F&V vs. the F&V (-2.8±1.0mm Hg) and AWD diets (-5.4±1.0mm Hg; diet x group interaction, P<0.02).
Other Findings
  • The concentration of RBC magnesium was significantly higher after the D-F&V diet (P=0.0010) vs. both the F&V and AWD diets (2.7±0.1, 2.3±0.1, 2.3±0.1, respectively)
  • Urine calcium was significantly elevated on the D-F&V diet (P=0.0214) vs. both the F&V and AWD diets (126.5±16.4, 87.8±16.0, 107.2±17.3, respectively)
  • Urine potassium was significantly elevated on the D-F&V diet (P=0.0001) vs. both the F&V and AWD diets (3,334±+238, 2,510±+237, 1,983±265, respectively)
  • Measures in serum calcium, iPTH, calcitonin and renin activity, RBC potassium, RBC sodium and urine sodium did not differ significantly between diets.
Author Conclusion:
Consumption of dairy foods beneficially affects (Ca)i, resulting in improved BP in a sub-group defined by (Ca)i response.
Funding Source:
Industry:
National Dairy Council
University/Hospital: General Clinical Research Center, the Pennsylvania State University
Reviewer Comments:
  • All participants were Caucasian
  • Control diet likely was healthier than participants’ habitual diet
  • Small sample size
  • Not all subjects completed all diet periods.
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? 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? ???
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? 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? 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.) 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? ???
  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? ???
  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? 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? 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? 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