Child Nutrition and Environment
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.
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.
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.
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).
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.
- 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.
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).
- 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.
Government: | Agency for Healthcare Research and Quality; Department of Health and Human Services |
- 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
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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? | 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 | |