Pediatric Weight Management

Child Nutrition and Environment

Citation:

Bell JF, Wilson JS, Liu GC. Neighborhood Greeness and 2 Year Changes in Body Mass Index of Children and Youth. Am J Prev Med. 2008 (Dec); 35 (6): 547-553.

 
Study Design:
Retrospective Cohort Study
Class:
B - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

This study was designed to test whether greenness and residential density were independently associated with two-year changes in Body Mass Index (BMI) of children and youth and whether the associations were modified by race or ethnicity, gender, age or socio-economic status.

Inclusion Criteria:

Electronic medical records of children aged three years to 16 years, who received routine medical care in a primary care clinic network in Indianapolis, IN (Marion County) between 1996 and 2002, who lived at the same address for at least 24 months and who had same-day clinical measurements of height and weight recorded two years apart were included. 

Exclusion Criteria:

Records were excluded if:

  • Diagnosis which would bias BMI measurement (e.g., pregnancy, congenital heart disease, cystic fibrosis, cerebral palsy, congenital anomalies)
  • Address was less than one km from the county boundary.
Description of Study Protocol:

Recruitment

Retrospective review of electronic medical records did not require recruitment.

Design

Cohort study comparing Normalized Difference Vegetation Index (NDVI; i.e., Greenness) for address with BMI measurements, age, ethnicity or race, gender and socio-economic status.

Statistical Analysis

  • BMI Z-scores were used to capture subtle changes in pooled data over time, with an additional dichotomous variable to categorize expected increase from Time One to Time Two
  • Geodata software, Moran's One was used to test spacial auto-correlation of dependent variable (i.e., people of similar weight living near each other, creating biased estimates)
  • Stata version 10.0 for ANOVA, multiple linear regression models, F-tests, logistic regression and other comparisons (P≤0.05 significance).
Data Collection Summary:

Timing of Measurements

  • Electronic Medical Records from 1996 to 2002 were reviewed for patients with at least a 24-month span of living at same address and height and weight data two years apart
  • Greenness evaluation from June 6, 2000, was chosen due to low cloud cover and close to peak vegetation growth
  • Analysis of data was conducted from 2007 to 2008.

Dependent Variables

  • Body Mass Index (BMI) change (kg/m2)
  • Greenness per Normalized Difference Vegetation Index (NDVI).

Independent Variables

  • Race or ethnicity
  • Age
  • Gender
  • Socio-economic status.

Control Variables

Not specified.

Description of Actual Data Sample:
  • Initial N: 3,901
  • Attrition (final N): 3,831 (51% male)
  • Age: Three years to 16 years (median, 9.16)
  • Ethnicity: 58% non-Hispanic black
  • Other relevant demographics
    • 83% on Medicaid
    • Obesity: 23%
    • Average block group median family income: $36,917 per year (lower than county average of $49,387 per year).
  • Anthropometrics:  Height and weight measures were used to calculate Body Mass Index
  • Location: Marion County, Indianapolis, Indiana, USA.

 

Summary of Results:

Key Findings: Linear Regression of Neighborhood Greenness and Residential Density on BMI Z-Scores
Beta-values (95% confidence interval) and P-values (significance ≤0.05).

  NDVI Residential Density NDVI + Residential Density
Health Insurance (Private: Medicaid) 0.01
(-0.07, 0.09)
P=0.87
-0.02
(-0.10, 0.06)
P=0.58
0.01
(-0.07, 0.09)
P=0.86
Median Family Income 0.02
(-0.01, 0.05)
P=0.30
-0.01
(-0.03, 0.03)
P=0.86
0.01
(-0.02, 0.04)
P=0.44
Baseline BMI Z-Score 0.76
(0.69, 0.76)
P<0.01
0.73
(0.69, 0.76)
P<0.01
0.73
(0.69, 0.76)
P<0.01
NDVI -0.06
(-0.09, -0.02)
P<0.01
Not applicable -0.07
(-0.11, -0.03)
P<0.01
Residential Density Not applicable -0.01
(-0.01, 0.01)
P=0.99
-0.01
(-0.01, 0.01)
P=0.06

NDVI: Normalized Difference Vegetation Index
BMI: Body Mass Index.

Other Findings

  • Relationships between NDVI and Time Two BMI Z-scores were significantly modified by insurance status (F-test, P<0.01)
  • Higher greenness was associated with lower odds of increasing BMI Z-scores (OR, -0.87; 95% CI, -0.79, 0.97).
Author Conclusion:
  • Greenness is inversely associated with BMI Z-scores of children and youth, independent of residential density, gender, age and race or ethnicity
  • The promotion and preservation of green space in neighborhoods could be a component of addressing childhood obesity.
Funding Source:
Government: Agency for Healthcare Research and Quality; Department of Health and Human Services
Reviewer Comments:
  • The sample was predominantly African-American and economically disadvantaged. Therefore, we question extrapolation to other groups.
  • Statistical analysis was extensive.
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? No
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.) 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? 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? N/A
  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? No
  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? 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)? 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? 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