DLM: Hypertension (2001)
To test the effects of dietary patterns on blood pressure.
- More than 22 years of age
- Average systolic blood pressure (SBP) less than 160mmHg
- Average diastolic blood pressure (DBP) 80 to 95mmHg
- Persons with medication-treated hypertension if above criteria for blood pressure met after supervised withdrawal of medication.
- Poorly controlled diabetes mellitus
- Hyperlipidemia
- Cardiovascular event within the past six months
- Chronic disease that would interfere with participation
- Pregnancy or lactation
- BMI greater than 35kg per m2
- Use of meds that affect blood pressure
- Unwillingness to discontinue vitamin/mineral supplements or antacids containing magnesium or calcium
- Renal insufficiency
- More than 14 alcoholic drinks per week.
Multicenter, randomized feeding study
- Three screening visits
- Run-in phase in which subjects received the control diet
- Randomized to one of the following diets for an eight-week intervention
- Control diet
- Potassium, magnesium and calcium levels close to the 25th percentile of US consumption
- Macronutrients and fiber corresponded to average consumption
- Sodium ~3g per day
- Diet rich in fruits/vegetables
- Potassium and magnesium levels close to the 75th percentile of US consumption
- High amounts of fiber
- Fewer snacks and sweets
- Sodium ~3g per day
- Combination diet rich in fruits, vegetables and low fat dairy products and reduced in saturated fat and total fat and cholesterol
- Potassium, magnesium and calcium at levels close to the 75th percentile of US consumption
- High amounts of fiber and protein
- Sodium ~3g per day
- Control diet
Statistics
- Hypotheses
- Change in blood pressure would differ between the combination and control diets
- The change in blood pressure would differ between the fruit/vegetable and control diets
- Change in blood pressure would differ between the combination and fruit/vegetable diets
- For primary analyses and within each subgroup stratum, between diet differences in the change in blood pressure were tested by two way analysis of variance, with adjustment for clinical center
- To adjust for multiple comparisons, a between diet difference was considered statistically significant at P<0.025 (two tailed); 97.5% CI are given for between diet differences
- Outcome measurements
- Primary: Change in DBP at rest
- Secondary: Changes in SBP and changes in systolic and ambulatory DBP and SBP.
SV*1 | SV2 | SV3 | R**1 | R2 | R3 | I***1 | I2 | I3 | I4 | I5 | I6 | I7 | I8 | |
Blood pressure measurement | x | x | x | x | x | x | x | x | x | x | x | x | x | |
Physical activity questionnaire | x | x | ||||||||||||
24 Hour urine | x | x | ||||||||||||
Symptom questionnaire | x | x | ||||||||||||
Randomization | x |
*SV: Screening visit **R: Run-in Phase, weeks ***I: Intervention Diet, weeks
- Initial sample: N=459
- Final sample: N=459
Characteristics of the Subjects According to Diet*
Control Diet | F/V Diet | Combination Diet | |
N=154 | N=154 | N=151 | |
Characteristics | |||
Age, yr |
44±11 | 45±11 | 44±10 |
Female, % |
47.4 | 48.7 | 51.0 |
Ethnicity, % | |||
Nonminority |
35.1 | 35.7 | 31.1 |
Black |
59.7 | 58.4 | 61.6 |
Other minority |
5.2 | 5.8 | 7.3 |
Household income, % | |||
<$30,000 |
37.1 | 36.7 | 36.0 |
$30,000-$59,999 |
41.7 | 36.7 | 42.7 |
≥$60,000 |
21.2 | 26.7 | 21.3 |
Weight, kg | |||
Men |
87.7±13.7 | 86.6±13.9 | 88.0±15.7 |
Women |
75.4±12.2 | 77.1±12.5 | 78.9±11.7 |
BMI | |||
Men |
27.7±3.6 | 27.5±3.6 | 28.1±4.0 |
Women |
28.3±4.0 | 28.9±4.3 | 29.0±3.9 |
BP med discontinued, % | 5.8 | 5.8 | 4.6 |
Ever received BP med, % | 20.8 | 25.3 | 20.5 |
Alcohol, drinks per week | 1.3±2.5 | 1.1±2.2 | 1.3±2.5 |
Blood pressure | |||
Systolic, mmHg ≥140, %¥ |
132±10.7 | 132±2.2 | 131.2±10.0 |
Diastolic, mmHg ≥90, %¥ |
85.3±4.0 | 84.8±3.9 | 35.1±3.6 |
Ambulatory systolic, mm Hg§ |
130.9±11.3 | 132.0±10.8 | 131.9±10.7 |
Ambulatory diastolic, mm Hg§ |
83.3±7.4 | 83.9±8.0 | 83.6±6.8 |
* Plus-minus values are means±SD
¥ Means for three screening visits
§ Mean 24-hour blood pressures in subjects in enrollment groups 2 to 5 (control [N=118], F/V [N=121] and combination [N=115] diets)
- Location of Clinical Centers
- Brigham and Women's Hospital and Harvard Medical School, Boston, MA
- Duke University Medical Center, Durham, NC
- Pennington Biomedical Research Center, Louisiana State University, Baton Rouge, LA
- Johns Hopkins University, Baltimore, MD.
Comparison of Mean Changes in Blood Pressure (mmHg)
Category | N |
Change in Combination Group minus Change in Control Group (97.5% CI) |
P-Value | Change in Combination Group Minus Change in Fruit/Veg Group (97.5% CI) | P-Value | Change in Fruit/Veg Group Minus Change in Control Group (97.5% CI) | P-Value |
Systolic Pressure | |||||||
All subjects | 459 | -5.5 (-7.4 to -3.7) | <0.001 | -2.7 (-4.6 to -0.9) | 0.001 | -2.8 (-4.7 to -0.9) | <0.001 |
Men | 234 | -4.9 (-7.3 to -2.5) | <0.001 | -1.6 (-4.0 to 0.8) | 0.13 | -3.3 (-5.6 to -0.9) | 0.002 |
Women | 225 | -6.2 (-9.2 to -3.3) | <0.001 | -3.9 (-6.9 to -1.0) | 0.003 | -2.3 (-5.3 to 0.7) | 0.08 |
Minority | 303 | -6.8 (-9.2 to -3.3) | <0.001 | -3.2 (-5.6 to-0.8) | 0.003 | -3.6 (-6.1 to -1.2) | 0.001 |
Nonminority | 156 | -3.0 (-5.9 to -0.1) | 0.02 | -1.9 (-4.8 to 1.0) | 0.13 | -1.1 (-3.9 to 1.7) | 0.38 |
Nonhypertensive | 326 | -3.5 (-5.3 to -1.6) | <0.001 | -2.7 (-4.5 to -0.8) | 0.001 | -0.8 (-2.7 to 1.1) | 0.33 |
Hypertensive | 133 | -11.4 (-15.9 to -6.9) | <0.001 | -4.1 (-8.6 to 0.3) | 0.04 | -7.2 (-11.4 to -3.0) | <0.001 |
Diastolic Pressure | |||||||
All subjects | 459 | -3.0 (-4.3 to -1.6) | <0.001 | -1.9 (-3.3 to -0.6) | 0.002 | -1.1 (-2.4 to 0.3) | 0.07 |
Men | 234 | -3.3 (-5.1 to -1.5) | <0.001 | -1.3 (-3.2 to 0.5) | 0.10 | -2.0 (-3.7 to -0.2) | 0.01 |
Women | 225 | -2.7 (-4.8 to -0.7) | 0.003 | -2.5 (-4.6 to -0.5) | 0.006 | -0.2 (-2.3 to 1.9) | 0.83 |
Minority | 303 | -3.5 (-5.2 to -1.8) | <0.001 | -2.1 (-3.8 to -0.4) | 0.007 | -1.4 (-3.2 to 0.3) | 0.07 |
Nonminority | 156 | -2.0 (-4.2 to 0.2) | 0.04 | -1.6 (-3.8 to 0.5) | 0.09 | -0.4 (-2.5 to 1.7) | 0.70 |
Nonhypertensive | 326 | -2.1 (-3.6 to -0.5) | 0.003 | -1.8 (-3.4 to -0.3) | 0.009 | -0.3 (-1.9 to 1.3) | 0.71 |
Hypertensive | 133 | -5.5 (-8.2 to -2.7) | <0.001 | -2.6 (-5.4 to 0.1) | 0.03 | -2.8 (-5.4 to -0.3) | 0.01 |
- Combination diet reduced mean 24-hour ambulatory SBP by 4.5mmHg more than the control diet and DBP by 2.7mmHg more (P<0.001 for each)
- Fruit and vegetable diet reduced mean 24-hour ambulatory SBP by 3.1mmHg more (P=0.001) than the control diet and DBP 2.1mmHg more (P=0.002).
Adverse Events
- Occurrence of GI symptoms was infrequent and similar for all the diets
- During run in phase, moderate or severe constipation in the preceding month was reported by 9% of subjects
- At the end of intervention phase, constipation was reported by 10.1% (control diet), 5.4% (fruit/vegetable diet) and 4.0% (combination diet).
Adherence
- Completion of intervention phase
- 95.5% (control diet)
- 97.4% (fruit/vegetable diet)
- 98.7% (combination diet)
- Self-reported adherence to study diets (all study food, no non-study foods)
- Control diet: 94.6% of person-days
- Fruit/vegetable diet: 93.9% of person-days
- Combination diet: 93.2% of person-days
- Urinary potassium increased from the run in phase to the intervention phase in the fruit/vegetable diet and combination group diets and magnesium excretion increased in the combination group
- Urinary urea nitrogen increased withthe combination diet
- Urinary calcium excretion decreased in the control and fruit/vegetable diet groups
- Urinary phosphorus excretion increased in the combination group
- Urinary sodium excretion changed little in each group between the run-in and intervention phases.
Other
- Mean changes in weight from end of run in to end of intervention phase: -0.1kg (control diet), -0.3kg (fruit/vegetable diet), and -0.4kg (combination diet)
- Mean changes in alcohol consumption and physical activity were small and similar in the three groups.
- A diet rich in fruits and vegetables and low-fat dairy foods and with reduced saturated fat and total fat can substantially lower blood pressure
- This diet offers an additional nutritional approach to preventing and treating hypertension.
Government: | NHLBI, Office of Research on Minority Healthy, NCRR |
- Well-controlled study
- Combination diet contained: 25.6% fat, 151mg cholesterol, 4,415mg potassium, 480mg magnesium, 1,265mg calcium and 2,359mg sodium.
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? | 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) | No | |
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%.) | Yes | |
4.3. | Were all enrolled subjects/patients (in the original sample) accounted for? | Yes | |
4.4. | Were reasons for withdrawals similar across groups? | ??? | |
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)? | 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? | Yes | |
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 | |