EAL

HTN: Minerals (2007)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

This analysis of the NHANES III was designed to investigate the impact of dietary calcium intake on age-related changes in blood pressure and pulse pressure.

Inclusion Criteria:

20 years or older.

Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment: NHANES III data - a stratified multistage probability sample of the US population
Design: Cross-sectional study
Blinding used: Not applicable
Intervention: Blood pressure readings, 24-hour dietary recall.

Statistical Analysis

Univariate and multivariate analyses were performed to assess the impact of reported daily calcium consumption on the rate of change of blood pressure with age. In the multivariate analysis, adjustments were made for demographics, BMI, and the other dietary factors. To develop the multivariate model, a random subsample was selected from the total sample and was used to select the best set of variables to be included in the final models. Standard stepwise regression and best subset regression were the statistical methods used for the selection of these variables. Principal component analysis was also used. The model was then tested on the remaining subsample using multiple weighted regression to adjust for the stratified design.

Data Collection Summary:

Timing of Measurements

Blood pressure readings and 24-hour dietary recall completed per participant.

Dependent Variables

Blood pressure (the mean of 3 readings)
Pulse pressure (calculated by subtracting DBP from SBP)

Independent Variables

Dietary calcium intake obtained via 24-hour recall questionnaire
Other dietary factors potentially affecting blood pressure: sodium, potassium, magnesium, protein, alcohol, and total energy in kcals

Control Variables

Demographics (age, gender, ethnicity)
Anthropometric info (weight, height, BMI)

Description of Actual Data Sample:

Initial N: 39,695 total participants, only 17,030 participants were 20 years or older

Attrition (final N): 17,030 participants, 47% male, 53% female

Age: mean age 48.8 +/- 0.2 years

Ethnicity: 42% Caucasian, 28% African American, 26% Hispanic, 4% Other

Other relevant demographics: Mean BMI 27.1 +/- 0.2

Anthropometrics: There was no significant difference in total energy consumption between the ethnic and gender groups.

Location: United States

Summary of Results:

	Low Ca (<500)	Medium Ca (500-1200)	High Ca (>1200)
Rate of rise of SBP in mm Hg per 10 years of age	6.5 +/- 0.01	5.8 +/- 0.01	5.1 +/- 0.02
Rate of rise of PP in mm Hg per 10 years of age	5.5 +/- 0.09	4.8 +/- 0.08	3.8 +/- 0.01
Rate of DBP change in mm Hg per 10 years of age, before age 50	4.0 +/- 0.1	3.3 +/- 0.1	3.2 +/- 0.2
Rate of DBP change in mm Hg per 10 years of age, after age 50	-1.8 +/- 0.1	-2.3 +/- 0.2	-1.3 +/- 0.3

Other Findings

Overall, average calcium intake was 761 mg/day. Calcium intake was divided into 3 groups - low (<500 mg/day), moderate (500 - 1200 mg/day), and high (>1200 mg/day).

Caucasians consumed the highest amount of dietary calcium while African Americans consumed the least (p < 0.001). Males consumed more calcium than females (p < 0.001).

Total daily energy and calcium consumption decreased with age (p < 0.0001).

After adjusting for gender, ethnicity, BMI and total energy consumption, higher calcium intake was associated with lower rates of age-related increases of SBP and pulse pressure (p < 0.001). This remained true after adjusting for sodium, potassium, magnesium, alcohol and protein (p = 0.02).

Author Conclusion:

In conclusion, based on the analysis of the NHANES III data, we found that higher calcium intake (>1200 mg/day) was inversely associated with the age-related increase in pulse pressure and SBP. If the calcium intake of the general population were to increase to this level, then the incidence of isolated systolic hypertension in the elderly might be decreased. Potentially, this would have a significant impact on decreasing hypertension related morbidity and mortality.

Funding Source:

Reviewer Comments:

Controlled for many factors. Large sample size.

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)	N/A
	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.)	N/A
	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?		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?	N/A
	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?	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