title: Donation frequency, iron loss, and risk of cancer among blood donors.
abstract: BACKGROUND
  Long-term deleterious effects of repeated blood donations may be masked by the donors' healthy lifestyle. To investigate possible effects of blood donation and iron loss through blood donation on cancer incidence while minimizing "healthy donor effects," we made dose-response comparisons within a cohort of Swedish and Danish blood donors.
  
  
  METHODS
  We used a nested case-control study design, in which case patients were defined as all donors who were diagnosed with a malignancy between their first recorded blood donation and study termination (n = 10866). Control subjects (n = 107140) were individually matched on sex, age, and county of residence. Using conditional logistic regression, we estimated relative risks of cancer according to number of blood donations made or estimated iron loss 3-12 years before a case patient was diagnosed with cancer. All statistical tests were two-sided.
  
  
  RESULTS
  No clear association was observed between number of donations and risk of cancer overall. However, between the lowest (< or = median, < 0.75 g) and highest (> 90th percentile, > 2.7 g) categories of estimated iron loss, there was a trend (P(trend) < .001) of decreasing risk for cancers of the liver, lung, colon, stomach, and esophagus, which are thought to be promoted by iron overload (combined odds ratio [OR] = 0.70, 95% confidence interval [CI] = 0.58 to 0.84), but only among men and only with a latency of 3-7 years. The risk of non-Hodgkin lymphoma was higher among frequent plasma donors (> 25 vs 0 donations, OR = 2.14, 95% CI = 1.22 to 3.74).
  
  
  CONCLUSIONS
  Repeated blood donation was not associated with increased or decreased risk of cancer overall. The lack of consistency across latency periods casts doubt on an apparent association between reduced cancer risk and iron loss in men. The positive association between frequent plasma donation and risk of non-Hodgkin lymphoma deserves further exploration.
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Box 281, SE-171 77, Stockholm, Sweden. gustaf.edgren@ki.se
authors.forename: Gustaf
authors.initials: G
authors.lastname: Edgren
authors.forename: Marie
authors.initials: M
authors.lastname: Reilly
authors.forename: Henrik
authors.initials: H
authors.lastname: Hjalgrim
authors.forename: Trung Nam
authors.initials: TN
authors.lastname: Tran
authors.forename: Klaus
authors.initials: K
authors.lastname: Rostgaard
authors.forename: Johanna
authors.initials: J
authors.lastname: Adami
authors.forename: Kjell
authors.initials: K
authors.lastname: Titlestad
authors.forename: Agneta
authors.initials: A
authors.lastname: Shanwell
authors.forename: Mads
authors.initials: M
authors.lastname: Melbye
authors.forename: Olof
authors.initials: O
authors.lastname: Nyrén
mesh_terms: D001782:Blood Donors / Q000706:statistics & numerical data*; D016022:Case-Control Studies; D003110:Colonic Neoplasms / Q000453:epidemiology / Q000517:prevention & control; D015986:Confounding Factors, Epidemiologic; D003718:Denmark / Q000453:epidemiology; D004938:Esophageal Neoplasms / Q000453:epidemiology / Q000517:prevention & control; D005260:Female; D006801:Humans; D007501:Iron / Q000097:blood*; D008113:Liver Neoplasms / Q000453:epidemiology / Q000517:prevention & control; D008175:Lung Neoplasms / Q000453:epidemiology / Q000517:prevention & control; D008228:Lymphoma, Non-Hodgkin / Q000453:epidemiology / Q000209:etiology; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000097:blood / Q000453:epidemiology* / Q000209:etiology / Q000517:prevention & control; D016017:Odds Ratio; D018570:Risk Assessment; D012307:Risk Factors; D012737:Sex Factors; D013274:Stomach Neoplasms / Q000453:epidemiology / Q000517:prevention & control; D013548:Sweden / Q000453:epidemiology; D013997:Time Factors
chemical_list: D007501:Iron