School-based obesity interventions may need to be tailored by gender

A study of 17,000 U.S. adolescents finds that black and Hispanic girls are less physically active than white girls, but that this difference is attributable to the schools they attend: black, white and Hispanic girls attending the same school have no difference in physical activity.

In contrast, among boys, blacks and Hispanics were more physically active than whites attending the same schools.

The researchers, led by Tracy Richmond, MD, in the Division of Adolescent Medicine at Children's Hospital Boston, report and discuss their findings in the June issue of Pediatrics.

Richmond and colleagues carefully analyzed data from the National Longitudinal Study of Adolescent Health, a school-based study of 7th-to-12th graders.

"Obesity is a growing problem in all adolescents, but it affects racial and ethnic minorities disproportionately," Richmond says. "Since physical activity is one protective factor against obesity that we can influence, we wanted to know whether schools might help determine physical activity levels."

Their key findings are as follows:

• On average, black and Hispanic adolescents had a higher body mass index (BMI) than white adolescents.
  
• Overall, adolescent girls were less physically active than boys, reporting fewer physical activities per week.
  
• Overall, black and Hispanic girls reported less activity than white girls - an average of 5.4, 5.2 and 6.0 activities per week, respectively. In contrast, among boys, the number of activities per week was similar for blacks (7.6), Hispanics (7.5) and whites (7.6).
  
• Most adolescents attended schools that were racially segregated: nearly 40 percent of whites attended schools whose student bodies were more than 94 percent white, while about 80 percent of both blacks and Hispanics attended schools whose populations were less than 66 percent white.
  
• Black and Hispanic adolescents attended schools with lower median incomes (blacks, $30,000; Hispanics, $32,500; whites, $45,000).
  
• In general, black and Hispanic girls attended poorer schools in which all girls had lower physical activity levels. But when school factors were accounted for, there was no longer a racial/ethnic difference in physical activity among girls.
  
• Among boys, there were only minimal racial/ethnic differences in physical activity levels overall. But within the same schools, both black and Hispanic boys had higher rates of physical activity than white boys.
  
• Students with lower household incomes reported less physical activity. However, after taking into account the average household income of the schools' student body, individual household income was no longer significantly associated with physical activity in either males or females. "This suggests that poorer and richer students attending the same school have similar levels of physical activity," says Richmond.