EAL

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
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