title: Mortality and cancer incidence in the EPIC-NL cohort: impact of the healthy volunteer effect.
abstract: BACKGROUND
  Prospective cohort studies recruit relatively healthy population samples, resulting in lower morbidity and mortality rates than in the source population. This is known as the healthy volunteer effect. The aim of this study was to define the magnitude and the development over time of the healthy volunteer effect in the EPIC-NL cohort.
  
  
  METHODS
  We studied mortality rates in the EPIC-NL cohort, which comprises 37 551 men and women aged 20-70 years at recruitment in 1993-97. The date and cause of death of deceased participants until 2010 were obtained through linkage with the municipal registry and Statistics Netherlands. Standardized mortality ratios (SMRs) were computed by dividing the observed number of deaths by the number of deaths expected from the general Dutch population. Additionally, standardized incidence ratios were calculated to compare cancer incidence.
  
  
  RESULTS
  After an average follow-up of 14.9 years, 3029 deaths were documented. Overall mortality in men [SMR 73.5%, 95% confidence interval (CI): 68.1-79.3] and women (SMR 65.9%, 95% CI: 63.2-68.6) was lower compared with the general population for the whole follow-up period. The SMRs clearly increased over the follow-up period. Among women, the SMR was lower for death due to cardiovascular diseases than death due to cancer. Cancer incidence was also lower in EPIC-NL than in the general population (SMR 78.3 and 82.7% for men and women, respectively).
  
  
  CONCLUSIONS
  The results show a healthy volunteer effect in the EPIC-NL cohort, which tapers off with longer follow-up. Therefore, in the first years of follow-up, power might not be sufficient to detect small associations.
authors.affiliation: 1 Department of Epidemiology, Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, 3508 GA, Utrecht, The Netherlands 2 Centre for Nutrition, Prevention and Health Services, National Institute for Public Health and the Environment (RIVM), 3720 BA, Bilthoven, The Netherlands e.struijk-2@umcutrecht.nl.
authors.forename: Ellen A
authors.initials: EA
authors.lastname: Struijk
authors.affiliation: 1 Department of Epidemiology, Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, 3508 GA, Utrecht, The Netherlands.
authors.forename: Anne M
authors.initials: AM
authors.lastname: May
authors.affiliation: 1 Department of Epidemiology, Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, 3508 GA, Utrecht, The Netherlands.
authors.forename: Joline W J
authors.initials: JW
authors.lastname: Beulens
authors.affiliation: 1 Department of Epidemiology, Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, 3508 GA, Utrecht, The Netherlands.
authors.forename: Carla H
authors.initials: CH
authors.lastname: van Gils
authors.affiliation: 1 Department of Epidemiology, Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, 3508 GA, Utrecht, The Netherlands.
authors.forename: Evelyn M
authors.initials: EM
authors.lastname: Monninkhof
authors.affiliation: 1 Department of Epidemiology, Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, 3508 GA, Utrecht, The Netherlands.
authors.forename: Yvonne T
authors.initials: YT
authors.lastname: van der Schouw
authors.affiliation: 2 Centre for Nutrition, Prevention and Health Services, National Institute for Public Health and the Environment (RIVM), 3720 BA, Bilthoven, The Netherlands.
authors.forename: Monique W M
authors.initials: MW
authors.lastname: Verschuren
authors.affiliation: 2 Centre for Nutrition, Prevention and Health Services, National Institute for Public Health and the Environment (RIVM), 3720 BA, Bilthoven, The Netherlands.
authors.forename: Jolanda M A
authors.initials: JM
authors.lastname: Boer
authors.affiliation: 2 Centre for Nutrition, Prevention and Health Services, National Institute for Public Health and the Environment (RIVM), 3720 BA, Bilthoven, The Netherlands 3 Department of Gastroenterology and Hepatology, University Medical Centre Utrecht, 3508 GA, Utrecht, the Netherlands.
authors.forename: Bas H
authors.initials: BH
authors.lastname: Bueno-de-Mesquita
authors.affiliation: 1 Department of Epidemiology, Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, 3508 GA, Utrecht, The Netherlands.
authors.forename: Petra H M
authors.initials: PH
authors.lastname: Peeters
mesh_terms: D000328:Adult; D000368:Aged; D015982:Bias; D002423:Cause of Death; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D006306:Health Surveys / Q000379:methods / Q000706:statistics & numerical data*; D064368:Healthy Volunteers / Q000706:statistics & numerical data*; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000453:epidemiology*; D009426:Netherlands / Q000453:epidemiology; D011446:Prospective Studies; D012042:Registries / Q000706:statistics & numerical data; D015203:Reproducibility of Results; D012307:Risk Factors; D017678:Sex Distribution; D055815:Young Adult