HTN: Magnesium (2015)
Citation:
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To evaluate dietary habits among groups with different blood pressure status (normotensive, non-medicated hypertensive, medicated hypertensive) in a representative sample of a Spanish Mediterranean population and to analyze the association between blood pressure and intakes of sodium, potassium, magnesium and calcium in normotensive and non-medicated hypertensive subjects and in those undergoing hypertension drug treatment.
Inclusion Criteria:
Non-institutionalized Spanish men and women, between ages of 25 and 74.
Exclusion Criteria:
None specifically mentioned.
Description of Study Protocol:
- Recruitment: 3,000 subjects randomly selected from province of Gerona from September 1994 to January 1996
- Design: Cross-sectional study
- Intervention: Blood samples, blood pressure, questionnaires.
Statistical Analysis
- Analysis of means by a general linear model was used to calculate the participant characteristics
- ANCOVA used to estimate dietary intake according to blood pressure status
- A post-hoc Bonferroni correction for multiple comparisons was carried out to determine differences in nutrient intake between groups
- The odds ratio of inadequate blood pressure control for recommended daily calcium and moderate sodium intakes was analyzed with logistic regression, adjusted for age, sex, BMI, smoking and drinking status
- Linear regression analysis was carried out after adjusting for the above-mentioned potential confounders to analyze the association of systolic and diastolic blood pressures with sodium, calcium, potassium and magnesium intakes.
Data Collection Summary:
Timing of Measurements
Blood samples, blood pressure, questionnaires.
Dependent Variables
- Cardiovascular risk measurements by MONICA-WHO study hypertension questionnaire
- Blood samples analyzed for total and HDL cholesterol, triglycerides
- LDL calculated by Friedewald equation
- Body weight by precision scale
- Blood pressure determined by mercury sphygmomanometer.
Independent Variables
Analysis of dietary intake reported on validated 72-hour recall by trained interviewer.Control Variables
- Age
- Sex
- BMI
- Smoking
- Drinking.
Description of Actual Data Sample:
Initial N
- 3,000 subjects selected
- 2,404 eligible after excluding census errors
- 1,748 (72.7%) agreed to participate.
Attrition (Final N)
- 986 normotensive (47.7% men, 52.3% women)
- 371 non-medicated hypertensive subjects (53.1% men, 46.9% women)
- 210 subjects undergoing drug treatment (43.3% men, 56.7% women).
Age
- Normotensive: Mean, 45.1±12.5 years
- Non-medicated hypertensive: 58.6±11.1 years
- Medicated hypertensive: 62.0±9.6 years.
Ethnicity
Not mentioned.
Location
Spain.
Summary of Results:
Normotensive and Non-Medicated Hypertensive Subjects (N=1,357) | Odds Ratio | 95% Confidence Interval |
Calcium RDA (>800 mg/day) | 0.85 | 0.63-1.13 |
Moderate Na (<2,400 mg/day) |
0.70 |
0.52-0.94 |
Moderate NA and Calcium RDA | 0.67 | 0.50-0.91 |
Magnesium RDA (>350 mg/day for men, >280 mg/day for women) | 0.91 | 0.63-1.31 |
Potassium RDA (>3,500 mg/day) |
1.05 |
0.79-1.39 |
Medicated Hypertensive Subjects (N=210) | Odds Ratio | 95% Confidence Interval |
Calcium RDA (>800 mg/day) | 0.57 | 0.27-1.19 |
Moderate Na (<2400 mg/day) |
0.56 |
0.22-1.39 |
Moderate NA and Calcium RDA | 0.48 | 0.24-0.95 |
Magnesium RDA (>350 mg/day for men, >280 mg/day for women) | 0.59 | 0.38-1.47 |
Potassium RDA (>3500 mg/day) |
0.75 |
0.25-1.41 |
Other Findings
- Nutrient intake was similar among groups of different blood pressure status after adjusting for age, sex and energy consumption
- Multiple linear regression analyses revealed a highly significant inverse correlation between calcium intake and SBP and DBP in the non-hypertension medicated study population. Sodium intake and the sodium-to-potassium ratio were directly associated with DBP, whereas magnesium intake showed a direct association with SBP. Most importantly, the correlation between blood pressure and mineral intake was not only seen in the non-hypertension medicated study population, but was also found in the medicated hypertensive subjects.
- Multiple linear regression analysis, after adjustment for several confounders, showed that dietary intake of sodium was directly related to blood pressure. The same was seen for the sodium-to-potassium ratio and both were independent of hypertension drug treatment.
- In contrast, an inverse association was observed between blood pressure and dietary calcium intake
- Moderate sodium (under 2,400mg per day) intake reduced the risk of hypertension by 30% and 52% (odds ratio, 0.70; 95% CI, 0.52-0.94, respectively) in normotensive and non-medicated hypertensive subjects
- Furthermore, moderate sodium, in combination with a calcium intake of more than 800mg per day, reduced the risk of inadequate blood pressure control by 52% (odds ratio, 0.48; 95% CI, 0.24-0.95) in subjects undergoing hypertension drug treatment
- Dietary intakes of magnesium (over 350mg per d for men and over 280mg per day for women) and potassium (over 3,500mg per day) were not significantly related to hypertension
- Controlled hypertension subjects have a significantly higher calcium intake than non-controlled.
Author Conclusion:
- In conclusion, the sodium-to-potassium ratio and dietary intakes of calcium and sodium were related to blood pressure, independently of hypertension drug treatment
- Furthermore, moderate sodium (under 2,400 mg per day) intake reduced the risk of hypertension in normotensive and non-medicated hypertensive subjects
- Moreover, moderate sodium, in combination with a calcium intake of more than 800mg per day, reduced the risk of inadequate blood pressure control significantly in subjects undergoing hypertension drug treatment
- These findings emphasize the importance of diet as a non-pharmacological approach on the prevention and treatment of hypertension.
Funding Source:
University/Hospital: | fondo de investigacion sanitaria |
Reviewer Comments:
- Large sample size, controlled for many factors
- 72-hour dietary recall
- Validated questionnaires.
Quality Criteria Checklist: Primary Research
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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? | N/A | |
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? | N/A | |
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? | Yes | |
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 | |