title: Joint associations of physical activity and sedentary behaviors with body mass index: results from a time use survey of US adults.
abstract: OBJECTIVE
  Obesity risk is negatively associated with physical activity and positively associated with time spent in sedentary behaviors. Yet, it is not known how different combinations of sedentary and active behavior are associated with body mass index (BMI). This study examined the interaction between time spent in physical activity and sedentary behavior on BMI in US adults.
  
  
  METHODS
  Cross-sectional, data from the 2006 American Time Use Survey.
  
  
  METHODS
  10 984 non-underweight adults (aged 21 + years).
  
  
  METHODS
  A phone interview assessed all activities performed in the past 24 h, height, weight, health status, and other sociodemographic characteristics. Time spent in (1) moderate-to-vigorous leisure-time physical activity (MVPA), (2) active transportation (walking, biking), (3) sedentary leisure activities (TV/movie watching, computer use, playing games, reading), and (4) sedentary transportation (motorized vehicles) was determined from activity coding. BMI was calculated.
  
  
  RESULTS
  After adjusting for age, gender, education level, race/ethnicity, and health status, sample-weighted linear regressions found significant interactions for leisure MVPA x TV/movies, leisure MVPA x playing games, active transportation x sedentary transportation, and active transportation x reading (Ps<0.0001). For example, the group of adults watching <60 min per day of TV/movies and engaging in > or =60 min per day of leisure MVPA had lower average BMI compared to the group watching <60 min per day of TV/movies and reporting <60 min per day of leisure MVPA (P<0.0001). In contrast, for adults watching > or =189 min per day of TV/movies, there was not a significant difference in BMI by time spent in leisure MVPA.
  
  
  CONCLUSIONS
  Data from a US time use survey indicate that the strength of the association between certain types of sedentary behavior and BMI varies according to time spent in certain types of physical activity and vice versa.
authors.affiliation: Health Promotion Research Branch, Behavioral Research Program, Division of Cancer Control and Population Sciences, National Cancer Institute, Bethesda, MD, USA. dunton@usc.edu
authors.forename: G F
authors.initials: GF
authors.lastname: Dunton
authors.forename: D
authors.initials: D
authors.lastname: Berrigan
authors.forename: R
authors.initials: R
authors.lastname: Ballard-Barbash
authors.forename: B
authors.initials: B
authors.lastname: Graubard
authors.forename: A A
authors.initials: AA
authors.lastname: Atienza
mesh_terms: D000328:Adult; D015992:Body Mass Index; D003430:Cross-Sectional Studies; D005260:Female; D015438:Health Behavior; D006306:Health Surveys; D006801:Humans; D007407:Interviews as Topic; D007899:Leisure Activities; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D009765:Obesity / Q000453:epidemiology / Q000503:physiopathology*; D057185:Sedentary Behavior; D011795:Surveys and Questionnaires; D014481:United States / Q000453:epidemiology