EAL

HTN: Minerals (2007)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

The investigators designed this analysis of NHANES III data to describe regional variations in blood pressure and the reported consumption of nutrients, focusing on those linked to blood pressure.

Inclusion Criteria:

Obtained data on all individuals 18 years and older collected through NHANES III.

Exclusion Criteria:

No exclusion criteria was published.

Description of Study Protocol:

Recruitment: Multistage probability sampling of the United States
Design: Cross-sectional research design was used.

Statistical Analysis

To determine differences among the four regions, an analysis of variance (ANOVA) technique was used
Multivariate analyses were performed using multiple weighted regression analysis to perform covariate adjustments
For each blood pressure or dietary factor studied, a regression model was used to compare regional differences while controlling for age, gender, ethnicity, body mass index (BMI) and total reported energy consumption.

Data Collection Summary:

Timing of Measurements

Not applicable.

Dependent Variables

Systolic blood pressure (SBP)
Diastolic blood pressure (DBP).

Independent Variables

Age
Gender
Ethnicity
BMI
Dietary intake (24-hour questionnaire), including dietary factors linked to blood pressure and additional factors for descriptive reasons (protein, carbohydrates, total fatty acids, saturated fatty acids, monounsaturated fatty acids, cholesterol and fiber; sodium, potassium, calcium, magnesium, zinc, copper and iron, vitamins C, E, riboflavin, B-6, B-12, niacin and thiamin; and alcohol).

Control Variables

Investigators controlled for age, gender, ethnicity, BMI and total reported energy consumption.

Description of Actual Data Sample:

Initial N: 17,752 participants from NHANES III (53% female)
Attrition (final N): Not applicable
Age: 47.6±0.2 years
Ethnicity: 41% white, 27% black, 27% Hispanic, 4% other ethnicities. Ethnicity did vary according to region, with the South having the greatest proportion of blacks and the West having the greatest proportion of Hispanics.
Other relevant demographics: Of the total sample, 43% (N=3,444) represented the South region of the US, 24% (N=4,175) of the sample was from the West, 19% (N=3444) from the Midwest and 14% (N=2,473) from the Northeast.
Anthropometrics: BMI was significantly different among all four regions, with the South recording the highest mean BMI (27.13±0.07) and the Northeast having the lowest mean BMI (26.70±0.12)
Location: Not applicable, as an administrative database was used (NHANES III).

Summary of Results:

Variable	Overall (All Regions)	Northeast	Midwest	South	West	P Value
Age, years	47.6±0.2	50.2±0.4	49.1±0.4	47.6±0.2	44.8±0.3	<0.05
Males, %	47	44	46	47	48	<0.05
Whites/blacks, %	41/27	54/34	58/28	37/36	27/9 (58% Hispanics	<0.05
BMI	26.97± 0.04	26.70±0.12	26.95±0.10	27.13±0.07	26.84±0.08	<0.05
SBP, mm HG	125±0.1	125±0.4	124±0.3	126±0.2	123±0.3	<0.05
DBP, mmHG	74±0.1	73±0.2	73±0.2	75±0.1	73±0.2	<0.05
Total Energy, kJ/day	8686±33	8581±92	8745±75	8636±54	8799±67	NS
Total Fat, g/day	79.0±0.4	75.2±1.0	80.2±0.9	80.3±0.6	78.2±0.8	<0.005
Carbohydrates g/day	254±1	257±3	254±2	249±2	259±2	<0.005
Protein, g/day	79±0.3	79±0.9	78±0.8	79±0.5	82±0.7	<0.005
Fiber, g/day	17±0.1	16±0.2	16±0.2	16±0.1	20±0.2	<0.005
Alcohol g/day	8.8±0.2	8.4±0.5	10.2±0.6	7.8 ±0.3	9.6±0.5	<0.005
Cholesterol mg/day	298±2	274±5	274±4	309±3	311±4	<0.005
Sodium g/day	3.3±0.01	3.3±0.01	3.3±0.03	3.4±0.02	3.2±0.03	<0.05
Potassium, g/day	2.7±0.01	2.7±0.03	2.7±0.02	2.6±0.02	2.8±0.02	<0.05
Phosphorus, g/day	1.2±0.01	1.2±0.01	1.2±0.01	1.1±0.01	1.3±0.01	<0.05
Calcium, mg/day	767±4	791±12	769±10	716±6	845±9	<0.05
Magnesium, mg/day	283±1	284±3	283±3	268±2	310±2	<0.05
Zinc, mg/day	11.4±0.1	11.1±0.2	11.3±0.2	11.3±0.2	11.9±0.2	<0.05
Copper, mg/day	1.3±0.01	1.3±0.02	1.3±0.02	1.2±0.02	1.4±0.02	<0.05
Iron, mg/day	14.6±0.1	15.2±0.2	14.5±0.2	14.1±0.1	15.1±0.2	<0.05

Other Findings

After adjusting for gender, age, ethnicity, BMI and total energy intake using multivariate analysis, the South region had the highest SBP (P<0.05) and DBP (P<0.05), the Midwest region had the lowest SBP (P<0.005) and the East region had the lowest DBP (P<0.05)
In addition, the South region had the highest consumption of monounsaturated fatty acid, polyunsaturated fatty acid and cholesterol (P<0.05)
Conversely, the East region ate the lowest amount of these nutrients (P<0.05)
After covariate adjustments, the South consumed the most sodum per day (P<0.005) and the least amounts of potassium, calcium, phosphorus, magnesium, copper and iron.

Author Conclusion:

The geographic analysis of the NHANES-III data confirmed previous studies that have found that higher mean blood pressure levels in the southern region of the US and such elevations may be associated with higher intakes of sodium and lower intakes of potassium, calcium, phosphorus, magnesium, copper, iron and fiber
The increased cardiovascular disease identified in the "stroke belt" may also be associated with higher reported intakes of cholesterol as well as by dietary patterns that may contribute to higher levels of blood pressure.

Funding Source:

University/Hospital:

University of South Carolina, Medical College of Wisconsin

Reviewer Comments:

This is a well-designed cross-sectional study that controlled for the key mitigating factors, which may influence rates of hypertension (gender, age, ethnicity, BMI)
It provides insight into future investigations for measuring dietary patterns of persons residing in the southern regions of the US and their impact on hypertension and cardiovascular disease.

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)	N/A

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?	Yes
	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?		N/A
	4.1.	Were follow-up methods described and the same for all groups?	N/A
	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%.)	N/A
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	N/A
	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?		???
	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?	???
	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?	N/A
	6.4.	Was the amount of exposure and, if relevant, subject/patient compliance measured?	N/A
	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?	N/A
	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?	No
	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