Pediatric Weight Management

PWM: Physical Activity and Inactivity of Youth (2006)

Citation:

Berkey CS, Rockett HRH, Gillman MW, Colditz GA, 2003. One-year change in activity and in inactivity among 10 to 15 year old boys and girls: Relationship to change in body mass index. Pediatrics. 111 (4): 836-843.

PubMed ID: 12671121
 
Study Design:
Longitudinal (Cohort Study)
Class:
C - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

To examine the relationships between one-year changes in total physical activity, season-specific activity, total inactivity, certain activities and in activities separately and concurrent changes in BMI.

Inclusion Criteria:

Part of the Growing up Today study.

Exclusion Criteria:
  • Height greater than three SD beyond the gender age-specific mean height
  • Any one-year change height that declined by more than one inch or increased by more than nine inches
  • BMI greater than 12kg per m2 was the biological lower limit and any BMI greater than three SD beyond the gender and age-specific mean.

 

Description of Study Protocol:

Recruitment

  • Offspring from the Nurses Health Study II were recruited for the Growing Up Today Study
  • Those with data for 1997 and 1998 were included
  • Response rate was 92% for girls and 88% for boys.

Design

In Fall of 1997 and again in 1998, participants were sent follow-up questionnaires to update all information.

Statistical Analysis 

  • Regression models with change in BMI as the continuous outcome. All models fit separately for boys and girls, included race, ethnic groups and energy intake to account for changes in BMI that normally occur during growth and maturation, height growth from 1997 to 1998, menstrual history (girls), age, tanner stage and BMI in 1997.
  • We fit a series of models denoted “S-models” because it examined a single activity or inactivity
  • A joint model was fit so that overweight and more lean children had separate estimates of the effects of each variable.
Data Collection Summary:

Dependent Variables

  • BMI: Self-reported height and weight
  • Change in BMI: BMI 1998 to BMI 1997
  • Overweight: Greater than the 85th percentile vs. those under the 85th percentile.

Independent Variables

  • Physical activity: Typical number of hours based on a recall over the past year; change in physical activity (PA) for aerobics, strength training and walking
  • Physical inactivity: Questions regarding TV, video watching and computer games (not homework).

Control variables

  • Race/ethnic group, maturation status (Tanner)
  • Age
  • Height change
  • BMI in 1997 (for the change data).
Description of Actual Data Sample:
  • 8,980 girls and 7,791 boys from 50 states that were offspring from the Nurses Health Study
  • 6,767 girls and 5,120 boys ages 10 to 15 years who had returned both surveys in 1997 and 1998
  • Mostly White, with BMI exceeding 85th percentile in 15.8% of girls and 22.6% of boys
  • For the multivariate analyses, 6,171 girls and 4,725 boys were included, who had complete data on the outcome measure and well as the covariates.

     
Summary of Results:

Boys

  • Increasing total PA-predicted BMI declines for overweight boys (-0.197kg/m2; CI -0.307, -0.086)
  • Overweight boys who increase waking (-0.402kb per m2; CI -0.701, -0.102) and aerobic dancing (-1.335kg per m2; -2.169, -0.501) had BMI declines, whereas increasing strength training did not increase BMI as it did among more lean males
  • Overweight boys lost BMI by increasing physical activity during each of the four seasons (Beta range = -0.051 to -0.168). The joint model confirmed that overweight boys lost BMI by increasing total activity (-0.160kg per m2; -0.294, -0.025).

Girls

  • For girls, an increase in PA from 1997 to 1998 was associated with a relative decline in BMI (-0.055kg per m2; CI -0.10, -0.01) and an increase in aerobic dancing was associated with an even larger BMI decline (-0.197kg per m2; CI -0.364, -0.030)
  • Increasing inactivity was associated with an increase in BMI (+0.045kg per m2; CI: +0.018, +0.073). For TV alone, the effects were stronger (+0.076; CI +0.036, +0.117).
Author Conclusion:
  • Evidence supports that, for girls and overweight boys, increasing total recreational physical activity over one year was associated with a relative BMI decline
  • We also found that increases in recreational inactivity was associated with larger BMI gains for girls
  • Increasing aerobic dance was associated with BMI declines in boys and girls, but walking was accompanied by BMI declines among overweight boys only
  • Season specific analyses revealed that increasing winter activity was strongly associated with BMI declines among overweight girls
  • Provides evidence that, in older children and adolescents, increasing recreation PA and reducing time watching TV or videos may be accompanied by reductions in adiposity.
Funding Source:
Government: Supported by grant DK46834 from NIH
Industry:
Not-for-profit
0
Foundation associated with industry:
Reviewer Comments:

Strengths

  • Large longitudinal, so change over time could be assessed and growth and maturation were controlled for
  • Although BMI data was self-reported, instructions were sent to help facilitate accurate measurements
  • Assistance with the measurements was available because all children were offspring from the Nurses Health Study, thus their mothers were nurses.

Limitation

  • Data was collected by a survey mailed to participants
  • The children had to self-report activity and inactivity (which has not been studied for reliability/validity)
  • This cohort of children was not a representative sample of US children (all children of Nurses, 94.7% White, etc.)
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) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? N/A
  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? Yes
  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.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? Yes
  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? 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? No
  6.6. Were extra or unplanned treatments described? No
  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)? No
  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