HTN: Calcium (2015)


Toledo E, Delgado-Rodriguez M, Estruch R, Salas-Salvado J, Corella D, Gomez-Gracia E, Fiol M, Lamuela-Raventos RM, Schroder H, Aros F, Ros E, Ruiz-Gutierrez V, Lapetra J, Conde-Herrera M, Saez G, Vinyoles E, Martinez-Gonzalez MA. Low-fat dairy products and blood pressure: Follow-up of 2,290 older persons at high cardiovascular risk participating in the PREDIMED study. Br J Nutr. 2009; 101: 59-67.

PubMed ID: 18492300
Study Design:
Prospective Cohort Study
B - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
To assess the relationship between low-fat dairy product intake and BP in an observational follow-up study conducted in a large population at high cardiovascular risk and participating in the PREDIMED study.
Inclusion Criteria:
  • PREDIMED inclusion:
    • Men 55 years to 80 years or women 60 years to 80 years
    • No previously documented CVD but a high cardiovascular risk
    • Type 2 diabetes OR at least three of the following risk factors:
      • Current smoking
      • Hypertension
      • Hyperlipidemia
      • HDL-cholesterol less than 1.034mmol per L
      • Overweight or obesity
      • Family history of premature CHD.
  • For present analysis: Complete data at baseline and after 12 months follow-up
Exclusion Criteria:
For present analysis:
  • Extreme total energy intakes
  • Missing data at baseline or at 12 months.
Description of Study Protocol:


Current analysis used subject data from PREDIMED trial.


Prospective cohort study.

Blinding Used

Implied with measurements.


Not applicable for this analysis; modification of dairy intake was not part of the PREDIMED intervention.

Statistical Analysis

  • Food and nutrient intakes adjusted for total energy intake using the residual method
  • Participants divided into quintiles of low-fat dairy or whole-fat dairy consumption
  • Crude means for SBP and DBP across quintiles of dairy product consumption (separately for low-fat and whole-fat)
  • Multivariable linear regression models to control for potential confounders
  • Models constructed were adjusted and not adjusted for BMI
  • Five multivariable linear regression models fitted for each exposure (low-fat dairy and whole-fat dairy):
    • Baseline cross-sectional analysis (exposure baseline dairy consumption; outcome: baseline BP)
    • A 12-month cross-sectional analysis (exposure of 12-month dairy consumption; outcome of 12-month BP) 
    • Conventional longitudinal analysis (exposure of baseline dairy product consumption; outcome of BP at 12 months)
    • Longitudinal analysis with BP changes as outcome (exposure of baseline dairy product consumption; outcome of BP changes during follow-up)
    • Dynamic longitudinal analysis (exposure of changes in dairy product consumption; outcome of changes in BP at 12 months).
  • For linear trend analyses, each quintile of dairy consumption was assigned its median value
  • All significance levels were calculated two-sided.


Data Collection Summary:

Timing of Measurements

Baseline and 12 months.

Dependent Variables

Blood pressure is measured in triplicate with a validated semi-automatic oscillometer, then a mean of three SBP and three DBP is calculated.

Independent Variables

Dairy consumption is assessed through a semi-quantitative 137-item FFQ, with information about dairy products assessed in 15 items.

Control Variables

  • Presence of diabetes
  • Mean physical activity during previous year
  • Anti-hypertensive treatment, treatment with non-steroidal anti-inflammatory drugs or drugs that may modify serum Ca
  • Alcohol consumption
  • Use of potassium supplements
  • Total energy intake
  • Sodium intake
  • Consumption of fruits and vegetables
  • Non-dairy intake of potassium, calcium, magnesium and total protein
  • BMI.
Description of Actual Data Sample:
  • Initial N: N=2,392
  • Attrition (final N):  N=2,290 (37.3% to 73.8% females across quintiles of low-fat dairy consumption, P for trend<0.001).

Age (Years; Mean±SD)

  • Q1: 67.2±6.4
  • Q2: 66.7±6.1
  • Q3: 67.0±6.1
  • Q4: 67.7±5.9
  • Q5: 68.1±5.9
  • P for trend=0.001.
  • Baseline SBP, mm Hg (95% CI):
    • Q1: 152.7 (150.8, 154.6)
    • Q2: 150.0 (147.5, 152.5)
    • Q3: 147.8, 152.8
    • Q4: 150.9 (158.4, 153.4)
    • Q5: 148.8 (146.2, 151.3)
    • P for trend=0.01.
  • Baseline DBP, mm Hg (95% CI):
    • Q1: 84.9 (83.8, 85.0)
    • Q2: 83.5 (82.2, 84.9)
    • Q3: 83.6 (82.2, 84.5)
    • Q4: 84.2 (82.8, 85.5)
    • Q5: 82.4 (81.0, 83.8)
    • P for trend = 0.003.
  • BMI (kg/m2) (mean±SD):
    • Q1: 29.6±3.5
    • Q2: 29.5±3.5
    • Q3: 29.9±3.6
    • Q4: 29.7±3.7
    • Q5: 30.0±4.3
    • P=0.04.
  • Quintiles of low-fat dairy intake (g per day) (mean±SD):
    • Q1: 3.1±17.1
    • Q2: 14.1±53.3
    • Q3: 236.7±26.8
    • Q4: 406.1±80.1
    • Q5: 631.6±139.4.
  • Quintiles of whole-fat dairy intake (g per day) (mean±SD):
    • Q1: 261.1±218.3
    • Q2: 99.0±123.3
    • Q3: 60.9±63.9
    • Q4: 67.6±5.9
    • Q5: 68.1±5.9.




Summary of Results:

Key Findings

  • Cross-sectional analyses, baseline: Marginally significant inverse linear trends for changes in SBP across quintiles of low-fat dairy consumption in adjusted model.
    • Change SBP, mm Hg  (95% CI):
      • Q1: Ref
      • Q2: -2.7 (-5.2, -0.1)
      • Q3: -2.9 (-5.5, -0.3)
      • Q4: -1.9 (-4.5, 0.8)
      • Q5: -3.7 (-6.5, -0.9)
      • P for trend=0.05.
  • Cross-sectional analysis, 12-month: Significant inverse linear trends for changes in SBP and DBP across quintiles.
    • Change in SBP, mm Hg (95% CI):
      • Q1: Ref
      • Q2: -3.2 (-5.7, -0.8)
      • Q3: -2.2 (-4.7, 0.3)
      • Q4: -3.6 (-6.1, -1.1)
      • Q5: -4.5 (-7.1, -2.0)
      • P for trend=0.001.
    • Change in DBP, mmHg (95% CI):
      • Q1: Ref
      • Q2: -1.0 (-2.3, 0.2)
      • Q3: -1.1 (-2.4, 0.2)
      • Q4: -2.2 (-3.5, -1.0)
      • Q5: -1.4 (-2.7, -0.1)
      • P for trend=0.01.
  • Longitudinal analysis, baseline exposure, 12-month BP: Significant inverse linear trend across quintiles for changes in SBP.
    • Change in SBP, mm Hg (95% CI):
      • Q1: Ref
      • Q2: -2.8 (-5.3, -0.3)
      • Q3: -2.5 (-5.1, 0.03)
      • Q4: -2.2 (-4.8, 0.4)
      • Q5: -4.2 (-6.9, -1.4)
      • P for trend=0.01.
  • Other longitudinal comparisons:
    • Comparisons across extreme quintiles were not significant
    • Linear trend tests in longitudinal analysis with change in BP as an outcome or in dynamic longitudinal analysis were not significant
    • No significant trends were observed in the analyses using whole-fat dairy product consumption as an exposure.

Other Findings

The point estimates for the adjusted comparisons between extreme quintiles of whole-fat dairy product consumption had always had a positive sign except for one time, suggesting a modest non-significant positive association.
Author Conclusion:
Low-fat dairy products could play an important role in the prevention of hypertension and may be helpful in the control and reduction of BP levels.
Funding Source:
Government: Spanish Ministry of Health, Generalitat Valenciana
Reviewer Comments:
Total dairy intake was not analyzed.
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? 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.) 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? Yes
  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? 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? 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