title: Recreational physical activity and risk of papillary thyroid cancer among women in the California Teachers Study.
abstract: OBJECTIVE
  Little is known about the relationship between physical activity and thyroid cancer risk, and few cohort data on this association exist. Thus, the present study aimed to prospectively examine long-term activity and risk of papillary thyroid cancer among women.
  
  
  METHODS
  116,939 women in the California Teachers Study, aged 22-79 years with no history of thyroid cancer at cohort entry, were followed from 1995-1996 through 2009; 275 were diagnosed with invasive papillary thyroid cancer. Cox proportional-hazards regression provided relative risk (RR) estimates and 95% confidence intervals (CI) for associations between thyroid cancer and combined strenuous and moderate recreational physical activity both in the long-term (high school through age 54 years or current age if younger than 54 years) and recently (during the three years prior to joining the cohort).
  
  
  RESULTS
  Overall, women whose long-term recreational physical activity averaged at least 5.5 MET-hours/week (i.e. were active) had a non-significant 23% lower risk of papillary thyroid cancer than inactive women (RR = 0.77, 95% CI: 0.57, 1.04). RR estimates were stronger among normal weight or underweight women (body mass index, BMI<25.0 kg/m(2), trend p = 0.03) than among overweight or obese women (trend p = 0.35; homogeneity-of-trends p = 0.03). A similar pattern of risk was observed for recent activity (BMI<25 kg/m(2), trend p = 0.11; BMI≥25 kg/m(2), trend p = 0.16; homogeneity-of-trends p = 0.04). Associations for long-term activity did not appear to be driven by activity in any particular life period (e.g. youth, adulthood).
  
  
  CONCLUSIONS
  Long-term physical activity may reduce papillary thyroid cancer risk among normal weight and underweight women.
authors.affiliation: Department of Epidemiology, School of Public Health, University of Washington, Seattle, WA 98195, USA.
authors.forename: Stephanie Whisnant
authors.initials: SW
authors.lastname: Cash
authors.forename: Huiyan
authors.initials: H
authors.lastname: Ma
authors.forename: Pamela L
authors.initials: PL
authors.lastname: Horn-Ross
authors.forename: Peggy
authors.initials: P
authors.lastname: Reynolds
authors.forename: Alison J
authors.initials: AJ
authors.lastname: Canchola
authors.forename: Jane
authors.initials: J
authors.lastname: Sullivan-Halley
authors.forename: Shirley A A
authors.initials: SA
authors.lastname: Beresford
authors.forename: Marian L
authors.initials: ML
authors.lastname: Neuhouser
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Vaughan
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Heagerty
authors.forename: Leslie
authors.initials: L
authors.lastname: Bernstein
mesh_terms: D000328:Adult; D000368:Aged; D015992:Body Mass Index; D002140:California / Q000453:epidemiology; D002277:Carcinoma / Q000453:epidemiology* / Q000209:etiology; D002291:Carcinoma, Papillary / Q000453:epidemiology* / Q000209:etiology; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology*; D009765:Obesity / Q000150:complications / Q000453:epidemiology; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012307:Risk Factors; D000077273:Thyroid Cancer, Papillary; D013964:Thyroid Neoplasms / Q000453:epidemiology* / Q000209:etiology; D055815:Young Adult