The results of the present study showed that a community-based behavioral intervention to increase dietary CA intake and WBPA among 9–11 year old girls enrolled in the Girl Scouts program was not effective in increasing bone mass gains, or frequency of WBPA, over a two-year period. Significant increases in dietary CA intake were observed as a result of the intervention. However, all troops were close to recommended dietary CA levels throughout the study period. These null results were observed despite the documented high levels of troop intervention implementation and participation. Nevertheless, these results provide data that may be useful in designing future dietary and PA behavioral interventions that target youth in a community setting.
Reasons for the lack of significant effects of the intervention on behavior or bone changes are not clear. It is not surprising that no significant increases in bone mass changes were observed as a result of the intervention, since no significant changes in WBPA were produced, and CA intake was at recommended levels at baseline. Perhaps most surprising is the lack of behavior change observed among intervention troops, despite the high level of implementation and participation in the intervention activities. The troop leaders assigned to the intervention were well trained, motivated and thorough in their implementation of the intervention program activities during the troop meetings. Participation among girls was consistently high. The intervention activities comprised a significant portion of the troop meeting time for a two-year period.
These results suggest that a more structured intervention may be needed to impact WBPA changes when implemented in a community-based setting. Previous PA interventions that targeted bone mass changes among children were conducted using a more controlled intervention design. PA increases were achieved through supervised PA programs with a standardized frequency, duration and type of PA. [16
] By contrast, the behavioral intervention program implemented in the present study focused on educational activities, and behavioral skill-building such as goal-setting, self-monitoring and incentives. A more structured intervention, one that increases the frequency, intensity and duration of WBPA, may be needed to increase WBPA enough to impact bone mass gains. This type of structured intervention may be more easily implemented in a school-based setting in which daily physical education classes are part of the normal schedule. [18
] In addition, greater involvement of parents in structuring the home environment to increase WBPA and CA-rich food opportunities for their child may be needed to increase the magnitude of the intervention-related behavior changes and thereby increase bone mass gains. These more structured environmental intervention components may be coupled with a behavioral change intervention component for maximum effects on behavior change.
Baseline levels of CA intake and WBPA may also be important factors that influence the magnitude of the intervention effects on behavior changes. The girls in the present study had high baseline levels of CA intake, thus making further increases more challenging compared to a population with lower initial CA levels. Moreover, the high mean CA intake at baseline approached recommended intake for this age group (NIH, 1994). Additional CA may not have been associated with additional gains in bone mass even if the intervention was successful in producing further increases in CA intake. For the WBPA intervention component, a more frequent, structured, and supervised PA program and or a program that focuses on specific types of PA that are the most osteogenic, such as jumping, may prove more effective in increasing BMC gains.
Strengths of the present study include its strong study design, high level of implementation fidelity and participation, high-quality measurement of outcomes, and high levels of participant retention in the evaluation cohort. An additional strength was its implementation in a community-based youth group by trained community-based volunteers. Potential weaknesses include the use of a population with initially high levels of one of the behaviors targeted for increase (CA intake); lack of structure in the WBPA behavioral component; the use of an intervention without a strong environmental change component; and the reliance on self-report measures of PA.
The present study found that despite high levels of program implementation and participation, a community-based behavioral intervention to increase bone mass gains in 9–11 year old girls was not successful in changing bone mass outcomes or WBPA. Future research is needed to further explore the effectiveness of community-based behavioral interventions for dietary CA and WBPA increases that target children. However, a useful prelude to such research would be a series of additional controlled studies that examine physical activity dosages and the types of activities that produce the strongest effects on bone mass gains in targeted age groups. [20
] A similar set of systematic dosage studies for change in CA intake in populations that have an initially low or high CA level are needed. Together, the results of such studies could inform a more focused and potentially more effective behavioral intervention for bone mass gains targeting children that could be implemented in a free-living setting in the community.