EAL

DM: Prevention and Treatment of Cardiovascular Disease (2001)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To assess the effects of dietary patterns on blood pressure.

Inclusion Criteria:

Age of 22 years or older
Systolic BP <160 mm Hg
Diastolic BP 80-95 mm Hg

Exclusion Criteria:

poorly controlled diabetes mellitus
hyperlipidemia
cardiovascular event within the past 6 mo
chronic disease that would interfere with participation
pregnancy/lactation
BMI >35
Use of meds that affect blood pressure
unwillingness to d/c vitamin/mineral supplements or antacids containing Mg++ or Ca++
renal insufficiency
>14 alcoholic drinks per week

Description of Study Protocol:

Recruitment: mass mailings of brochures ad work-site and community-based screening were the primary recruitment strategies. One of the goals of the trial was to recruit a coort in which 2/3 of the subjects were members of a racial or ethnic minority.

Design: Multicenter, randomized controlled feeding study. Screening, followed by 3-week run-in phase where all subjects followed the control diet, followed by randomization into one of 3 diet interventions for 8 weeks.

Blinding Used: Staff members who took blood pressure measurements were blinded to diet assignment.

Intervention: Daily Nutrient Targets for Diets

	Control Diet	Fruits-Vegetables Diet	Combination Diet
Fat, % of total calories	37	37	27
Saturated Fat, % of total calories	16	16	6
Carbohydrates, % of total calories	48	48	55
Protein, % of total calories	15	15	18
Cholesterol, mg	300	300	150
Fiber, g	9	31	31
Potassium, mg	1700	4700	4700
Magnesium, mg	165	500	500
Calcium, mg	450	450	1240
Sodium, mg	3000	3000	3000

Food prepared in research kitchens and lunch and dinner eaten onsite. Weekend meals provided but eaten off-site.

Statistical Analysis

the target sample size of 456 randomly assigned subjects was estimated to provide 85 percent power to detect a mean between-diet difference of 2 mm Hg in diastolic blood pressure
Intention-to treat analysis performed. Missing blood pressure measurements were filled with baseline values.
primary analyses, subgroup stratums and between-diet differences in the change in blood pressure were tested by two-way analysis of variance, with adjustment for clinical center.
A between-diet difference was considered statistically significant at P<0.025 (97.5 CI)

Data Collection Summary:

Timing of Measurements:

Screening phase

Baseline blood pressure measured at each of 3 screening visits
Stanford 7-Day Physical Activity Recall questionnaire administered once during screening.

Control Diet Phase

2 blood pressure measurements obtained on each of 4 occasions during last two weeks of control period
24-hour urine sample
questionnaire on symptoms

Intervention Phase

blood pressure measured each week during first 6 weeks
during last two weeks, a pair of measurements was obtained on each of 5 different occasions.
24-hour urine sample
symptom questionnaire
activity questionnaire
body weight and sodium intakes were kept constant

Dependent Variables

Primary: Change in diastolic blood pressure at rest
Secondary: Ambulatory diastolic & systolic BP

Independent Variables

Adherence was measured using food records and 24-hour urinary excretiion of potassium, magnesium, urea nitrogen, calcium, phosphorus, and sodium during the run-in and intervention phases. Adherence was perfect on 93.2-94.6 percent of person-days.
Gender
Minority status
Diagnosis of hypertension

Control Variables

Description of Actual Data Sample:

Initial N: 8813 persons screened, 502 started the run-in phase. 459 subjects randomized. Baseline characteristics similar across diet groups.

Final N:

Completed control intervention: 95.5%
Completed fruit and vegetable intervention: 97.4%
Completed combination diet intervention: 98.7%

Age, Ethnicity, Other Relevant Demographics, and Anthropometrics

Selected characteristics of study subjects (No significant differences between groups):

Characteristic	Control Diet	Fruit/Veg Diet	Combination Diet
Age, years	44 ±11	45 ±11	44 ±10
Black or other minority, %	64.9	64.2	68.9
BMI-women	28.3 ±4.0	27.5 ±3.6	28.1± 4.0
BMI-men	27.7 ±3.6	28.9 ±4.3	29 ±3.9
Ever received BP medication, %	20.8	25.3	20.5

Location: Major medical centers throughout the US

Summary of Results:

	Change in Combination Group Minus Change in Control Group , mmHg	P Value	Change in Combination Group Minus Change in Fruits and Vegetables Group, mmHg	P Value	Change in Fruits and Vegetables Group Minus Change in Control Group, mmHg	P Value
Systolic Pressure
All Subjects	-5.5	<0.001	-2.7	0.001	-2.8	<0.001
Men	-4.9	<0.001	-1.6	0.13	-3.3	0.002
Women	-6.2	<0.001	-3.9	0.003	-2.3	0.08
Minority	-6.8	<0.001	-3.2	0.003	-3.6	0.001
Nonminority	-3.0	0.02	-1.9	0.13	-1.1	0.38
Nonhypertensive	-3.5	<0.001	-2.7	0.001	-0.8	0.33
Hypertensive	-11.4	<0.001	-4.1	0.04	-7.2	<0.001

Diastolic Blood Pressure
All subjects	-3.0	<0.001	-1.9	0.002	-1.1	0.07
Men	-3.3	<0.001	-1.3	0.10	-2.0	0.01
Women	-2.7	0.003	-2.5	0.006	-0.2	0.83
Minority	-3.5	<0.001	-2.1	0.007	-1.4	0.07
Nonminority	-2.0	0.04	-1.6	0.09	-0.4	0.70
Nonhypertensive	-2.1	0.003	-1.8	0.009	-0.3	0.71
Hypertensive	-5.5	<0.001	-2.6	0.03	-2.8	0.01

The combination diet lowered systolic and diastolic blood pressure by 5.5 and 3.0 mm Hg more, respectively than the control diet (P<0.001).

The fruits & vegetables diet lowered systolic blood pressure by 2.8 mm Hg more P<0.001) and diastolic blood pressure by 1.1 mm Hg more (P<0.07) than the control diet.

133 subjects with hypertension or systolic blood pressure >140 mm Hg , diastolic blood pressure >90 mm Hg or both, the combination diet lowered systolic and diastolic blood pressure by 11.4 and 5.5 mm Hg more, respectively, than the control diet (P<0.001, for each)

For the 325 subjects without hypertension, the corresponding reductions were 3.5 mm Hg (P<0.001) and 2.1 mm Hg (P<0.003).

Author Conclusion:

A diet rich in fruits and vegetables, and low-fat dairy foods and with reduced saturated and total fat can substantially lower blood pressure. This diet offers an additional nutritional approach to preventing and treating hypertension.

Funding Source:

Government:

NHLBI

Industry:

Merck and Company, Kaiser Permanente Center for Health Research, Best Foods, Campbell's Soup Company, Coca-Cola Foods Company, Comstock Michigan Fruit, The Dannon Company, Dole Food Company, H J Heinz Company, Harris Teeter Company, Hershey Foods Corp, Lifelines Technology Inc, McCormick & Company I

Food Company:

Pharmaceutical/Dietary Supplement Company:

Other:

University/Hospital:

Johns Hopkins University, brigham and Women's Hospital, Duke University Medical Center, Harvard School of Public Health, Pennington Biomedical Research Center

In-Kind support reported by Industry:

Yes

Reviewer Comments:

Well controlled study. This study included subjects with well controlled diabetes but did not present separate results for those with diabetes.

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?	N/A
	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%.)	N/A
	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?	???
	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?	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?	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)?	Yes
	8.5.	Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)?	???
	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