PWM: School-based Programs to Prevent Overweight (2006)
Walter HJ, Hofman A, Vaughan RD, Wynder EL. Modification of risk factors for coronary heart disease. Five-year results of a school-based intervention trial. New England Journal of Medicine, 1988; 318 (17): 1,093-1,100.PubMed ID: 3281016
- To evaluate the effectiveness of a school-based, teacher-delivered program designed to reduce specific risk factors associated with chronic disease in an eligible cohort of 3,388 children in the New York City area
- The aims of the study were to shift favorably the population distributions of levels of blood pressure, blood lipids, body mass and physical fitness through appropriate modifications in diet and physical activity, and to reduce the number of students starting to smoke cigarettes
- These results are after five years of intervention.
School children in two demographically dissimilar areas in and near New York City were selected as the eligible study populations (N=3,388)
- One population comprised students who were in the fourth grade in 1980 in all 22 elementary schools in a single school district (School District 11) in the Bronx, a lower-income borough of New York City (N=2,283)
- The second population comprised students who were in the fourth grade in 1979 in all 15 elementary schools in four districts (Byram Hills, Rye, Scarsdale and White Plains) in Westchester County, a middle- and upper- income suburb of New York City (N=1,105).
- The investigation was an intervention study involving two treatment conditions within each of the two study populations. At baseline in the Bronx, all 22 eligible elementary schools agreed to participate and the schools subsequently were randomly assigned to either the intervention (1,590 students in 14 schools) or the non-intervention (693 students in eight schools) treatment group. The method of random assignment was designed to assign approximately twice as many schools to intervention as to non-intervention. In the Bronx, student-migration patterns maintained the integrity of treatment assignment through high school. At baseline in Westchester, all four school districts agreed to participate in the study and were subsequently randomly assigned to either the intervention (485 students in eight schools) or the non-intervention (620 students in seven schools) group. To avoid condition crossover, it was necessary to assign students to treatment according to district, since all elementary schools in each Westchester district fed into a single high school. Pairs of districts were matched demographically before random assignment.
- Beginning in the fourth grade and continuing consecutively through the ninth grade (Westchester) or the either grade (Bronx), the intervention groups in both study populations were taught a special curriculum, entitled “Know Your Body,” aimed at the reduction of risk for the development of chronic disease. The non-intervention groups were not taught the special curriculum. Both groups were taught the state-mandated one-semester general health education curriculum at the junior high school level.
- The special curriculum targeted voluntary changes in risk-related behavior in the areas of diet, physical activity and cigarette smoking. The curriculum content was designed to provide the information and motivation necessary for behavioral changes, as well as training in the skills necessary to make such changes. The intervention foci (e.g., perceived susceptibility to, and severity of, health problems; perceived benefits of, and barriers to, adopting and maintaining risk-reducing types of behavior) were derived from the “health belief” model; skills-training strategies (e.g., modeling, rehearsal, practice, goal-setting, cueing and reinforcement) were derived from social-learning theory. Cognitive-development theory provided a framework for the appropriate tailoring of these constructs to the children’s changing maturational stages as the study progressed over a five-year period.
- The nutrition component of the curriculum promoted adoption of the “prudent” diet; reduced consumption of complex carbohydrates and fiber; increased ratio of polyunsaturated fat to saturated fat; and maintenance of ideal body weight. The physical-activity component of the curriculum fostered the adoption of a regular program of endurance exercise. The smoking curriculum was taught in classrooms of the schools assigned to intervention, by the specially trained regular teacher for approximately two hours per week throughout the school year. The research staff monitored the teachers to ensure their adherence to the special teaching protocols.
- The unit of intervention in this study was the school; thus, the school (rather than the student) was used as the unit of analysis. To determine the effectiveness of the intervention, the average changes in risk factors over the five-year course of the investigation were compared between schools in the intervention and non-intervention groups in the Bronx and Westchester separately. The changes in risk factors for individual subjects within schools were averaged to obtain an estimate of the mean change for each school. Estimates of the changes in risk factors in individual subjects were obtained by a linear regression analysis of each risk factor over time for each subject. The slope of the regression line served as an estimate of the average yearly changes in a subject’s risk factor. To be eligible for the slope analysis, subjects were required to have had risk-factor data collected at the study’s base line and at a minimum of two follow-up points. The mean changes in the risk factors for schools in the intervention and non-intervention groups were computed, together with their standard deviations. The net effect of the intervention was estimated by the differences in risk-factor change between the two groups of schools. The standard errors of those differences were used to calculate 95% CI around the differences. Similar analyses were performed for the scores on the test of health knowledge.
- The following additional analyses were performed. First, a linear regression model was used to adjust for differences between schools in the intervention and nonintervention groups at base line. In this model, the average change in risk factors for each school was the outcome variable. An indicator variable for intervention status (intervention, 1; non-intervention, 0) was entered as a determinant in the model, together with both the mean baseline risk-factor level and the percentage of White subjects in each school. The regression coefficient of the indicator variable for intervention status served as the estimate of the adjusted difference between the two groups of schools. The standard error of the coefficient was used to compute the 95% CI around the adjusted difference. Second, additional analyses of the effect on plasma levels of total cholesterol were performed in which each subject’s change in total cholesterol was calculated on the basis of data obtained at one of more follow-up points or at three or more follow-up points. In an additional analysis, the effects on changes in risk factors across baseline levels of risk factors were also computed.
- Of the 235 and 358 subjects randomly selected during the fourth-grade and ninth-grade school years, respectively, approximately 95% of both treatment groups in both populations participated at both measurement points. The means of dietary variables for individual subjects in each school were averaged to obtain mean values for all the schools. The net differences in change in the dietary variables between schools in the intervention and non-intervention groups were calculated and the standard errors of those differences were used to compute the 95% CI.
Levels of risk factors and health knowledge were measured in the autumn at baseline (fourth grade) and at four follow-up points (fifth, sixth, seventh and ninth grades) among consenting subjects in all schools assigned to intervention and non-intervention. The examining personnel and procedures were identical in the two populations. Examinations to determine levels of risk factors were conducted by trained professional personnel in the schools.
- In this model, the average change in risk factors for each school was the outcome variable
- Systolic blood pressure and diastolic blood pressure was measured with a Baum mercury sphygmomanometer on the right arm three consecutive times with the subject seated; diastolic pressure was based on the fourth Korotkoff sound. Nonfasting plasma levels of total cholesterol were measured at study base line and at the first follow-up point in an Auto-Analyzer II (Technicon, Tarrytown, N.Y.), with results adjusted to the standard reference of Abell-Kendall, and measured at subsequent follow-up points in a Gilford 3500 computer-directed analyzer (Gilford, Oberlin, Ohio) with use of enzymatic methods. A validation study comparing these two methods of measurement yielded results that were essentially identical (i.e., the same means and a correlation coefficient of 0.94). Plasma levels of high-density lipoprotein cholesterol were measured with use of the heparin-manganese chloride precipitation method. Serum thiocyanate (a metabolite of hydrogen cyanide) was measured at base line and at the first follow-up examination according to the method of Butts et al., and saliva cotinine (a metabolite of nicotine) was measure at subsequent follow-up points according to the method of Haley. Height and weight were measured with a standard medical balance beam scale with a rigid vertical height rod. The ponderosity index (weight in relation to height) was calculated according to a published formula. The protocol for the Harvard step test was modified for use among younger subjects to measure the recovery index (rate of pulse recovery after exercise).
- Students receiving intervention were given the results of the risk factor examination in the classroom, as part of the special curriculum. Individual levels of risk factors were classified as optimal or less than optimal and behavioral strategies were devised to modify levels needing improvement.
- In Autumn of the fourth-grade and ninth-grade school years, trained dietitians estimated current dietary practices by interviewing independent, randomly selected subsamples of consenting subjects in all the schools (following a modified protocol of Frank) regarding their diets during the previous 24 hours. The proportions of sex and racial or ethnic groups in the subsamples were similar to those in the entire populations. The nutrient compositions of the subjects’ self-reported dietary intake were analyzed with use of the Highland View Hospital-Case Western Reserve Nutrient Data Base (Revision, May 7, 1983). A questionnaire assess knowledge of the relation of diet, physical activity and tobacco use to the prevention of chronic disease was administered in the classroom by research staff to all consenting subjects in all the schools at baseline and at the four follow-up points.
- Students not receiving check this received their examination results by mail, with explanatory material and hygienic recommendations, as did the parents of all subjects in both the intervention and non-intervention groups
- Subjects whose risk-factor examination results exceeded the currently recommended cut-off points were referred to their usual sources of medical care for further diagnosis and treatment.
- Westchester County: 1105; Bronx: 2283
Number participated in examinations at baseline:
- Westchester County: 911 (82.4% overall: 92.1% receiving intervention; 74.9% not receiving it)
- Bronx: 1,563 (68.5% overall: 70.1% of those receiving intervention; 64.6% not receiving it):
- Total sample at baseline was 2,474.
Total total of 1,769 qualified for the analysis of the intervention effect:
- 733 in Westchester (80.5% overall: 84.1% receiving intervention; 77.0% not receiving intervention)
- 1,036 in Bronx (66.3% overall: 65.3% receiving intervention; 68.7% not receiving it).
15 schools in Westchester County; 22 schools in Bronx.
- Intervention: 89.8% White, 2.8% Black, 7.4%, other (primarily Hispanic)
- Control: 78.9% White, 15.1% Black, 6.0%, other (primarily Hispanic)
- Intervention: 31.7% White, 43% Black, 25.3%, other (primarily Hispanic)
- Control: 29.2% White, 48.7% Black, 22.1%, other (primarily Hispanic).
Not available; lower in the Bronx sample.
- Previously published data have demonstrated that study participants did not differ significantly from non-participants with respect to prevention-related knowledge and behavior measure at baseline. The mean (±SD) values for risk factors and test scores at base line among cohort subjects (N=1769) did not differ significantly from the values among subjects lost to follow-up (N=705).
- In Westchester, there was a new mean change in plasma levels of total cholesterol of -1.7mg per deciliter per year (-0.04mmol per liter) (95% CI, -2.7 to -0.7mg per deciliter [-0.07 to -0.02mmol per liter]). This corresponds to a net decline of -8.5mg per deciliter (-0.22mmol per liter), or 5.1%, over the five-year course of the investigation. A subgroup analysis according to sex suggested that the reduction in total cholesterol was greater among girls (-2.4mg per deciliter per year [-0.06mmol per liter]) (95%CI, -3.8 to -1.0mg per deciliter [-0.10 to -0.03mmol per liter]) than among boys (-0.0mg per deciliter per year [-0.02mmol per liter]) (95%CI, -2.2 to +0.5mg per deciliter [-0.06 to +0.01mmol per liter]). In the Bronx, the net change in plasma levels of total cholesterol was -1.0mg per deciliter per year (-0.03mmol per liter) (95% CI, -2.3 to +0.3mg per deciliter [-0.06 to +0.01mmol per liter]), or -5.0mg per deciliter (-0.13 mmol per liter) or 2.9%, over five years. Major sex-related differences in effect were not observed in the Bronx. There, the reduction in total cholesterol among girls was -0.9mg per deciliter per year (-0.02mmol per liter)(95% CI, -2.4 to +0.9 mg per deciliter [-0.06 to +0.02mmol per liter]); among boys, it was -1/2mg per deciliter per year (-0.03mmol per liter) (95% CI, -2.8 to +0.5mg per deciliter [-0.07 to +0.01mmol per liter]).
- Separate analyses in which adjustments were made for the baseline levels of total cholesterol and the percentage of white subjects in each school yielded results similar to the observed estimates.
- The net change in Westchester was -1.2mg per deciliter per year (-0.03mmol per liter) (95% CI, CI (-2.3 to –0.1mg per deciliter [-0.06 to -0.01mmol per liter]). In the Bronx, the net change was -0.8mg per deciliter per year (-0.02mmol per liter) (95%, -2.1 to +0.05mg per deciliter [-0.05 to +0.01mmol per liter]). Analyses including subjects on whom data were obtained at one or more follow-up points also yielded results similar to the observed estimates. In Westchester, the net change was -1.8mg per deciliter per year (-0.05mmol per liter) (95% CI, -2.9 to -0.7mg per deciliter [-0.007 to -0.02 mmol per liter]; significant change). In the Bronx, the net change was -0.4mg per deciliter per year (-0.01mmol per liter) (95%CI, -1.7 to +0.9mg per deciliter [-0.04 to +0.02mmol per liter]). Analyses including subjects with data obtained at three or more follow-up points also yielded similar results. Differential effects across baseline levels of total cholesterol were not observed.
- In Westchester, the net mean reduction in total fat intake was -3.6% (95% CI -7.1 to -0.1; significant) and the net mean increase in total carbohydrate consumption was +4.5% (95% CI +0.1 to +8.9; significant). For fat intake, the reduction was greater among girls (-4.2%; 95% CI, -8.4 to 0.0) than among boys (+0.9%; 95% CI -4.1 to +5.9). In the Bronx, the net mean reduction in the intake of saturated fat was -2.1% (95% CI -4.7 to +0.5); sex-related differences in effect were not observed.
- In Westchester, the net mean changes in the score on the test of health knowledge was +0.14 per year (95% CI +0.06 to +0.22); this corresponds to a net increase of +22.6% over five years. We observed greater net increases in the score among girls (+38.7%, as compared with +9.7% in boys). In the Bronx, the net mean increase in the score was +0.12 per year (95% CI +0.03 to +0.21), corresponding to a five-year net increase of 18.8%. Sex-related differences in effect were not observed in the Bronx.
Directly quoted from study:
- The principal finding of this study is that the intervention program appeared to be associated with favorable trends in blood levels of total cholesterol among two demographically dissimilar populations of school-children
- In the Westchester population, the net reduction in cholesterol levels was statistically significant, as were the net differences in reported dietary intakes of total fat and carbohydrate
- In the Bronx, the changes in blood cholesterol levels and dietary intake of saturated fat were in a favorable direction, but the confidence intervals of the net reductions included zero
- In both populations, there were significant net increases in prevention-related knowledge
- At the beginning of the ninth grade, the prevalence of cigarette smoking was still too low to permit detection of an effect on the number of subjects who started to smoke
- The program appeared to have no effects on either population on body mass, physical fitness, or blood pressure.
|University/Hospital:||Erasmus University Medical School (Netherlands)|
- The external validity of the study may have been affected by the non-participation of some of the eligible subjects in the baseline examination of risk factors and by the loss of some subjects to follow-up. However, the rates of participation and cohort retention in both populations were relatively high. Moreover, we found that participants were not significantly different from non-participants with respect to health knowledge and behavior measured at baseline and that subjects lost to follow-up were not significantly different from those remaining in the cohort with respect to baseline levels of risk factors and health knowledge.
- The internal validity of the study may have been compromised by differences in rates of participation between subjects in the schools in the intervention group and those in the non-intervention group schools. This conceivably could have lead to different baseline distributions of unmeasured determinants of change in risk factors, accounting in principle for part of the intervention effect.
- The internal validity of the study also may have been compromised by differential loss to follow-up of subjects who received intervention and those who did not
- Since a relatively small number of schools were involved in this study, the analysis according to school has limited statistical power. Moreover, the small number of units available for randomization may also account in part for some of the baseline differences between treatment groups.
- In this analysis, the slope of the regression line for each risk factor was used to estimate the average changes for each subject. The rationale for this approach is that multiple measurements over time may provide a better estimate of change than the simple difference between measurements obtained at the end of the study and those obtained at baseline.
- In subjects in both groups of schools, blood levels of total cholesterol declined over the course of the investigation. The decline in levels was greater among subjects receiving intervention than among those not receiving it, and the randomization procedure makes it unlikely that this difference was due to differences in the maturation of subjects in the two treatment conditions.
- The group of schools assigned not to receive intervention cannot be considered to have been no-treatment controls, since subjects at the schools underwent risk-factor examinations at the same time as the intervention students. Thus, control parents received the results of the exam, with explanatory material, hygienic advice, and referrals for students at high risk.
- Intervention was same for both areas, but language in curriculum was simplified in the Bronx to correspond to the lower reading levels in the community.
Quality Criteria Checklist: Primary Research
|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|
|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?||No|
|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?||No|
|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.)||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?||No|
|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?||No|
|4.4.||Were reasons for withdrawals similar across groups?||No|
|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?||No|
|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?||???|
|6.4.||Was the amount of exposure and, if relevant, subject/patient compliance measured?||No|
|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?||No|
|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?||No|
|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|