title: Longitudinal study of the long-term relation between physical activity and obesity in adults.
abstract: BACKGROUND
  Earlier observational studies of the relation between physical activity and obesity are inconsistent and ambiguous, showing a clear cross-sectional inverse relation, and a prospective association only when physical activity at the time of follow-up is included.
  
  
  OBJECTIVE
  To examine the long-term effect of leisure time physical activity (LTPA) on subsequent development of obesity and the effect of body weight on later physical inactivity in a population-based longitudinal setting taking into account the effects of historical changes on future changes as well as pertinent confounders.
  
  
  METHODS
  The study included 3653 women and 2626 men aged 20-78 y selected at random within sex-age strata from the general population of Copenhagen. At two surveys, 5 y apart, LTPA, body mass index (BMI) (weight/height2, kg/m2), several possible confounders and modifying factors were assessed. Obesity (defined as BMI > or =30 kg/m2) and LTPA was assessed at the 3rd survey 10 y later. Odds ratios (with 95% confidence limits) for developing obesity between the last two surveys were estimated by logistic regression analysis, taking into account baseline and preceding changes in BMI and LTPA. A similar analysis of odds ratios for physical inactivity as outcome at the 3rd survey was conducted.
  
  
  RESULTS
  Compared to physical inactivity, the odds ratios of development of obesity among women with medium and high level of activity were 0.81 (0.53, 1.25) and 1.16 (0.73, 1.84), respectively, and among men, the odds ratios were 1.28 (0.71, 2.33) and 1.65 (0.91, 2.99), respectively. Compared to median BMI, the odds ratio of later physical inactivity among women with high BMI was 1.91 (1.39, 2.61), and among men the odds ratio was 1.50 (1.01, 2.22). The associations were not confounded or modified by age, pre-existing diseases, smoking, alcohol intake, educational level, occupational physical activity or by familial predisposition to obesity.
  
  
  CONCLUSIONS
  This study did not support that physical inactivity as reported in the freely living adult population in the long term is associated with the development of obesity, but the study indicates that obesity may lead to physical inactivity.
authors.affiliation: Danish Epidemiology Science Centre at Institute of Preventive Medicine, Copenhagen University Hospital, Copenhagen K DK-1399, Denmark.
authors.forename: L
authors.initials: L
authors.lastname: Petersen
authors.forename: P
authors.initials: P
authors.lastname: Schnohr
authors.forename: T I A
authors.initials: TI
authors.lastname: Sørensen
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D015992:Body Mass Index; D003430:Cross-Sectional Studies; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000209:etiology*; D011446:Prospective Studies; D012044:Regression Analysis; D012737:Sex Factors