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NC: Cardiovascular Disease Risk Factors (2007-2008)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To investigate whether nonpharmacological interventions can prevent hypertension over the long term: Results of the Trials of Hypertension Prevention (TOHP) II.

Inclusion Criteria:
  • Overweight adults; body mass index (BMI) of 26.1 to 37.4kg per m2 for men and 24.4 to 37.4kg per m2 for women (approximately 110% to 165% of ideal weight)
  • Non-medicated diastolic blood pressure of 83 to 89mmHg and systolic blood pressure less than 140mmHg
  • Age 30 to 54 years.
Exclusion Criteria:
  • Current treatment with medications that might affect blood pressure
  • Clinical or laboratory evidence of cardiovascular disease, diabetes mellitus or renal insufficiency
  • Current or planned pregnancy.
Description of Study Protocol:

Recruitment

Eligible participants from nine TOHP Centers.

Design 

  • Eligible participants were randomly assigned to one of four groups:
    • Weight loss only
    • Sodium reduction only
    • Combined weight loss and sodium reductions
    • Usual care (controls)
  • This report compares the weight reduction group and control group.

Blinding Used 

Clinic staff, who made study assessments were blinded to study group assignment.

Intervention 

  • Participants assigned to the weight loss intervention group sought to lose at least 4.5kg (10 pounds) during the first six months of the intervention and maintain their weight loss for the remainder of the trial
  • The intervention included individual counseling, group meetings and special group sessions
  • The intervention focused on self-directed behavior change with focuses on dietary intervention and increased physical activity.

Statistical Analysis

  • Baseline characteristics of the weight loss and usual care groups were compared overall and by sex by using T-ests for means and chi-square tests for proportions
  • Two sample T-tests were used to compare changes in weight and blood pressure from baseline in the weight loss intervention and usual care groups overall, by sex, by ethnicity and by sex and ethnicity
  • The effects of the intervention in terms of changes in weight and blood pressure were examined overall and in subgroups defined by sex, ethnicity and sex and ethnicity
  • Subgroup differences were tested using multiple linear regression models
  • All regressions were adjusted for age and baseline weight
  • Changes in blood pressure were also examined in relation to quintile of weight loss
  • Quintiles were computed by using the distribution of weight change in the weight loss intervention group
  • Additional multiple regression analyses were performed in which weight loss participants were categorized according to patterns of weight loss at six and 36 months.
Data Collection Summary:
  • Timing of measurements: Baseline, six months, 12 months, 18 months and 36 months
  • Dependent variables: Weight loss and blood pressure
  • Independent variables: The weight loss intervention included a three-year program of group meetings and individual counseling focused on dietary change, physical activity and social support
  • Control variables: None.

 

Description of Actual Data Sample:
  • Initial N: 1191 (782 males; 409 females)
  • Attrition (final N): Not stated
  • Age: 43.3±6.1 years
  • Ethnicity: White 78.8%; Black 17.5%
  • Other relevant demographics: College graduates 50.8%
  • Location: Nine TOHP Centers. 

Anthropometrics: Baseline Characteristics

 
Weight Loss Group
(N=595)
Usual Care Group
(N=596)
Overall (N=1191)
Weight (kg)
Men
Women
 
98.8±12.3
84.1±11.9
 
98.5±11.7
82.9±10.9
 
98.7±12.0
83.6±11.5
Body Mass Index (kg/m2)
Men
Women
 
31.0±2.9
31.0±3.6
 
31.0±2.9
30.8±3.5
 
31.0±2.9
30.9±3.6
Systolic Blood Pressure (mmHg)
127.6±6.1
127.3±6.4
127.4±6.2
Diastolic Blood Pressure (mmHg)
86.0±1.9
85.8±1.9
85.9±3.1
Vigorous Exercise (times/week)
2.0±4.0
1.8±1.9
1.9±3.1
Energy Intake (kJ/24 h)
2.0±4.0
1.8±1.9
1.9±3.1
Energy from Fat (%)
36.0±9.6
33.9±10.3
34.9±10.0
Energy from Saturated Fat (%)
12.2±3.9
11.2±4.1
11.7±4.0

 

Summary of Results:

  

Weight Change
All Participants
Intervention (N)
Intervention
Control (N)
Control
 Difference
6 months

N=565
-4.4 (-4.8 to -3.9)

N=561
0.1 (0.1 to 0.4)
-4.5 (-5.0 to -4.0)
 
18 months  N=545   -2.0 (-2.5 to -1.5)  N=551  0.7 (0.4 to 1.6)  -2.7 (-3.3 to -2.1)
36 months   N=547     -0.2 (-0.7 to 0.3)

 N=554

  1.8 (1.3 to 2.2)  -2.0 (-2.6 to -1.3)
All Men          
6 months
 

N=358
   -5.1 (-5.7 to -4.5)
    

N=387
0.1 (-02 to 0.4)
-5.2 (-5.9 to -4.6)
   
18 months  N=348  -2.5 (-3.1 to -1.8)  N=381  0.8 (0.4 to 1.3)  -3.3 (-4.1 to -2.5)
36 months

N=355

 -0.7 (-1.3 to -0.1)

N=384

  1.9 (1.4 to 2.4)
-2.6 (-3.4 to -1.8)
All Women          
6 months
 

N=207
   -3.1 (-3.7 to -2.5)
    

N=174
0.2 (-0.3 to 0.7)
-3.3 (-4.0 to -2.5)
  
18 months  N=197   -1.2 (-2.0 to -0.5)  N=170 0.4 (-0.2 to 1.1)  -1.7 (-2.6 to -.07)
36 months   N=203  0.7 (-0.2 to 1.5)

 N=170

  1.5 (0.6 to 2.4)

 -0.8 (-2.0 to 0.4)
White Persons          
6 months
 

N=442
 -4.9 (-5.4 to -4.4)

N=446
0.1 (-0.2 to 0.4)
      
-5.0 (-5.6 to -4.4)
18 months N=422   -2.5 (3.1 to-1.9) N=442 0.6 (0.2 to1.0) -3.1 (-3.8 to -2.4)
36 months

N=426

  -0.4 (-1.0 to 0.2)

N=444

  1.6 (1.1 to 2.1)
-2.0 (-2.8 to -1.3)
Black Persons          
6 months
 

N=101
   -2.3 (-3.1 to -1.5)

 N=96
0.4 (0.2 to 1.0)
-2.7 (-3.6 to -1.7)
18 months N=99   -0.2 (-1.1 to 0.7) N=91 0.7 (-0.1 to 1.5) -0.9 (-2.1 to 0.3)
36 months

N=96

 0.7 (-0.4 to 1.9)

N=91

  2.2 (1.2 to 3.2)
-1.5 (-2.9 to 0.0)
Diastolic Blood Pressure          
6 month
 
  
 
  
 
-2.7 (95% CI -3.5 to 02.0; P<0.001)
18 month          -1.3 (CI -2.0 to -0.6; P<0.001)
  36 month         -0.9 (CI -1.7 to -0.0; P<0.05)
Systolic Blood Pressure          
6 month
 
  
 
  
 
-3.7 (CI -4.7 to -2.8; P<001) 
18 month         -1.8 ( CI -2.7 to -0.9; P<0.001)
  36 month         -1.3 (CI -2.4 to -0.3; P<0.01)

Other Findings

Change in Body Weight by Number of Counseling Sessions Attended

Baseline to 6 months
6 to 18 months
18 to 36 months
Counseling Sessions Participants (N) Mean Weight Change Counseling Sessions Participants (N) Mean Weight Counseling Sessions Change Counseling Sessions Participants (N) Mean Weight Change
0-2
3.9
10-13
14
 44
133
166
226
-2.2
-1.5
-4.2
-6.6
P<0.001
0-2
3-10
11-20
>20
68
199
208
60
2.3
2.9
2.8
1.6
P <0.031
0-2
3-10
11-20
>20
128
176
127
93
2.2
1.8
1.4
1.6
P>0.2

 

Author Conclusion:
  • The weight loss intervention in TOHP produced significant weight loss over 36 months compared with usual care, resulting in significant reductions in diastolic blood pressure and systolic blood pressure and in a lower incidence of hypertension
  • A direct dose-response relationship was observed between weight loss and blood pressure reduction
  • Weight loss at six months was strongly related to attendance at intervention sessions, but the relationship between attendance and weight loss diminished later in the trial
  • The findings suggest that some degree of weight loss confers benefit, even if not sustained beyond six months.
Funding Source:
Reviewer Comments:
  • This large study, part of the Trials of Hypertension Prevention-Phase II, demonstrates that weight loss can help with blood pressure control
  • The intervention of intensive nutrition counseling appears to have an effect on achieving weight loss that can be sustained for six months
  • As noted in the discussion of this study, the challenge is to develop weight loss programs that achieve higher long-term success rates.
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.) 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? ???
  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%.) ???
  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? Yes
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? Yes
  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? Yes
  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? 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