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NC: Behavior Change Strategies (2007-2008)

Citation:
Barrera M, Toobert D, Angell K, Glasgow R, Mackinnon D. Social support and social-ecological resources as mediators of lifestyle intervention effects for type 2 diabetes. J Health Psychology. 2006; 11 (3): 483-495.
PubMed ID: 16774900
 
Study Design:
Randomized controlled trial
Class:
A - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

The purpose of this study is to evaluate social resources as mediators of the effects of a comprehensive lifestyle intervention on the health of women with Type 2 diabetes.

Inclusion Criteria:
  • Female
  • Post-menopausal
  • Diagnosed with Type 2 diabetes for at least six months
  • Living independently (i.e., not in an institution)
  • Has a telephone
  • Able to read English
  • Not developmentally disabled
  • Lives within 30 miles of the intervention site.
Exclusion Criteria:
  • More than 75 years of age
  • Planning to move from the area within the study's time span of two years
  • Does not meet the above inclusion criteria
Description of Study Protocol:

Recruitment

  • Study subjects were recruited from participating primary care medical clinics
  • Researchers intention was to recruit subjects who would not actively seek out supplemental treatment on their own
  • Eligible patients were sent a letter from their primary care physicians, followed by a telephone call inviting them to participate. 

Design

  • A total of 116 participants were randomized to usual care (UC) and 163 to the Mediterranean Lifestyle Program (MLP)
  • In assignment to experimental conditions, participants were stratified on:
    • Physician practice
    • Smoking status
    • Type of diabetes medication
  • More participants were assigned to the MLP condition to accomodate an 18-month extension of the study that further divided the MLP condition into two groups to compare long-term maintenance strategies. 

Intervention

  • Participants in the MLP group began a six-month intervention with a three-day retreat during which women were taught all program components
  • Retreats were followed by weekly meetings consisting of an hour each of physical activity, stress management, a Mediterranean potluck diet and support groups
  • Participants received manuals that detailed each aspect of the MLP:
    • Diet: An RD taught participants the Mediterranean alpha linolenic acid-rich diet. RD individualized carbohydrate and fat requirements to optimize blood glucose and lipid concentrations within the parameters of the MLP.
    • Physical activity: Participants advised to build up to one hour of moderate aerobic activity per day, at least three times per week. Weekly meetings were led by an exercise physiologist.
    • Stress management: Participants were instructed in yoga, progressive deep relaxation, meditation and directed or receptive imagery and asked to practice the techniques for at least one hour per day
    • Support groups: Led by one professional with at least a master's education and one peer leader.  

Statistical Analysis

Regression model was estimated for each social resource variable and regression analyses used to show significant intervention effects on pre- to post-changes in the social resource scales: Social Support Survey (MOS), Social Network Index and the Chronic Illness Resource Survey (CIRS). 

Data Collection Summary:

Timing of Measurements

Variables measured at baseline and at six months.  

Dependent Variables

  • Variable one: CIRS; Measures individual's frequency of using resources from more proximal support (family and friends) to more distal factors (support from health care team, etc.) 
  • Variable two: MOS; A 19-item Social Support Survey measuring perceived availability of functional support. Items assessed five dimensions of social resources: emotional, informational, tangible, positive social interaction and affection.
  • Variable three: Social Network Index; A structural measure of social integration that assessed social network diversity. One point given for the presence of each of 12 social relationships with whom a participant had contact at least once every two weeks. Scores reflected not only existence of social relationships, but also frequency of contact with them.
  • Variable four: Percent calories from fat; Assessed using Food Frequency Questionnaire developed by Fred Hutchinson Cancer Center for the Women's Health Initiative
  • Variable five: Caloric expenditure per week (CHAMPS); Instrument developed for sedentary populations and tested primarily in older adults. Consists of 41 items with frequency of activity assessed in times per week and duration classified using six categories ranging from less than one hour per week to nine or more hours per week.
  • Variable six: HbA1c; Assayed with ion exchange high-performance liquid chromatography conducted at Oregon Medical Laboratories in Eugene, OR.

Independent Variables

  • Variable one: Age
  • Variable two: Income
  • Variable three: Hormone replacement therapy.

Control Variables

Usual physician care.

Description of Actual Data Sample:

Initial N

  • 276 Women
  • UC: 116  
  • MLP: 163.

Attrition (final N)

  • 245 (88%)
  • UC: N=137 (93%)  
  • MLP: N=137 (84%).

Participant Demographics

Characteristics                                     UC   (Mean or Percentage)                       MLP  (Mean or Percentage)                                         
Age 60.7 61.2
Income Intervals 3.6 3.9
Hormone Replacement Therapy* 46.6 59.3
CIRS 2.7 2.7
MOS 3.9 4.0
Social Network Index 5.8 5.9
% Calories from Fat 38.1 38.6
CHAMPS 3388.1 3030.4
HbA1c 7.6 7.4

* Two groups were significantly different P=0.037.

Summary of Results:

 Regressions With and Without Pre- to Post-Changes in Social Resource Variable (CIRS)

Variables

Caloric Expenditure (CHAMPS)

Without Mediator

B, SE B

Caloric Expenditure (CHAMPS)

With Mediator

B, SE B

% Calories from Fat (FFQ)

Without Mediator

B, SE B

% Calories from Fat (FFQ)

With Mediator

B, SE B

HbA1c

Without Mediator

B, SE B

HbA1c

With Mediator

B, SE B

Age

 -10.89,  29.76  -14.91,  29.12

 0.000, 0.001

 0.000,  0.001 -0.004,  0.007 -0.003,  0.007

Income

 -61.65,  106.24

 -94.83,  104.31

 -0.002,  0.002

 -0.001,  0.002  0.010,  0.026  0.019,  0.026

HRT

 771.31,  452.04

 792.84,  441.88

 0.004,  0.010

 0.003, 0.010  0.126, 0.112  0.116, 0.110
Treatment  1375.38**,  436.62  1056.93**,  437.26  0.053**, 0.010  -0.046**,  0.010  -0.299**, 0.109 -0.224*, 0.110 
CIRS   N/A  1407.72,  420.90  N/A  -0.030**, 0.009  N/A  -0.317**, 0.106

 *P<0.05

 **P<0.01

 Other Findings

  • Results showed changes in the social-ecological resources assessed by the CIRS-mediated intervention effects on all of the outcome criteria: Caloric expenditure per week from all physical activity, percentage of calories from fat and HbA1c
  • Changes in the extensiveness of social ties (the Social Network Index) mediated the intervention's effect on physical activity
  • The measure of perceived availability of social support (MOS) was not affected by the intervention and did not show mediation effects.
Author Conclusion:
  • The comprehensive six-month Mediterranean Lifestyle Program (MLP) was successful in changing social embeddedness and social-ecological resources, but not as a measure of perceived support
  • Social ecological resources can contribute to improvements in healthful lifestyles for women with Type 2 diabetes.
Funding Source:
Reviewer Comments:

Short, six-month complex study with multiple measures (fat consumption, physical activity and blood glucose control) to test the effects of perceived support, social embeddedness and social-ecological resources.

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%.) Yes
  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? 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? 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? N/A
  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? 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? N/A
  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? N/A
  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