Caregiver App Use and Child Behavioral Adherence in Relation to Obesity-Related Outcomes in an mHealth App-Assisted Childhood Obesity Intervention: Secondary Analysis of a Cluster Randomized Trial.

BACKGROUND: Childhood obesity remains a major public health challenge. Mobile health (mHealth) interventions offer a scalable approach to support behavior change, but their effectiveness may depend on participant adherence. While both caregiver and child adherence are important, few studies have jointly examined caregiver app-use adherence and child behavioral adherence within digital obesity interventions. OBJECTIVE: This study aimed to evaluate the independent and joint associations of caregiver app-use adherence and child behavioral adherence with obesity-related outcomes in a school-based mHealth intervention. METHODS: We conducted a secondary analysis of 684 child-caregiver dyads in the intervention arm of the diet, exercise, and cardiovascular health-children cluster-randomized trial, implemented across 3 socioeconomically diverse regions in China. Caregiver app-use adherence was measured using app-recorded app-use frequency and total usage duration. Child behavioral adherence was assessed through weekly behavior monitoring scores covering diet, screen time, and physical activity. Linear mixed models estimated associations between adherence levels and changes in anthropometric and physical fitness outcomes over 9 months. RESULTS: Higher caregiver app-use frequency and duration were both significantly associated with reductions in children's obesity-related indicators, such as BMI (β=-0.19; P=.005), BMI z-score (β=-0.08; P=.006), and body fat percentage (BFP) (β=-0.70; P=.005) for frequency. Greater child behavioral adherence was associated with lower BFP (β=-0.63; P=.01) and better physical fitness, including shorter shuttle run time (β=-3.63; P<.001) and longer standing long jump distance (β=2.88; P=.005). App-use frequency and duration showed a significant interaction for rope-skipping performance (P=.05). In joint adherence analyses, children in the high caregiver-high child adherence group showed the most favorable changes, including lower BMI (β=-0.22; P=.02), lower BFP (β=-1.18 percentage points; P=.001), and 7.45 additional rope-skipping repetitions (P=.003), compared with the low caregiver-low child adherence group. CONCLUSIONS: In this secondary analysis of an mHealth app-assisted childhood obesity intervention, higher caregiver app-use adherence and child behavioral adherence were associated with more favorable changes in weight status and physical fitness. These findings underscore the importance of coengagement in digital health programs and highlight the potential of app-supported, family-engaged strategies for childhood obesity prevention.