Summertime changes in sleep, physical activity, and BMI in urban minority girls

Purpose: Seasonal variations in weight gain among children are well documented. Urban minority and overweight youth are at higher risk for weight gain during the summer months, which may result from decreases in physical activity (PA) and sleep. While research has established links between PA, sleep, and BMI, the current study is the first to examine associations between summertime changes in these variables.

Methods: Participants (n=25) were 10-14-year-old low-income urban girls enrolled in a summer sports camp program. Most identified as African-American (n=11) or Latina/Hispanic (n=12) and nearly half (48%) were overweight/obese. Data was collected in the week prior to camp (T1) and during the final week of camp (T2). Anthropometric measurements were used to calculate zBMI. Actigraphs (GT3X) were used to measure PA (e.g., vigorous activity; VPA) and sleep (e.g., duration, efficiency).

Results: Sleep duration increased from T1 to T2 (t(24)=2.23, p=.036), as did VPA (t(23)=3.22, p=.004) and zBMI (t(23)=2.41, p=.024). zBMI change was negatively correlated with sleep efficiency change (r=-.41, p=.045). Controlling for T1 zBMI, only sleep efficiency change (β=-.057, p=.04) was significantly associated with T2 zBMI. VPA change predicted T2 zBMI after controlling for T1 zBMI (F-Change (1,20)=5.46, p=.03).

Conclusions: Taken together, results indicate that increases in PA and sleep efficiency may be powerful protective factors against summer weight gain in an at-risk sample.