title: Ultraviolet radiation exposure and risk of malignant lymphomas.
abstract: BACKGROUND
  The incidence of malignant lymphomas has been increasing rapidly, but the causes of these malignancies remain poorly understood. One hypothesis holds that exposure to ultraviolet (UV) radiation increases lymphoma risk. We tested this hypothesis in a population-based case-control study in Denmark and Sweden.
  
  
  METHODS
  A total of 3740 patients diagnosed between October 1, 1999, and August 30, 2002, with incident malignant lymphomas, including non-Hodgkin lymphoma, chronic lymphocytic leukemia, and Hodgkin lymphoma, and 3187 population controls provided detailed information on history of UV exposure and skin cancer and information on other possible risk factors for lymphomas. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated by logistic regression. Statistical tests were two-sided.
  
  
  RESULTS
  Multivariable-adjusted analyses revealed consistent, statistically significant negative associations between various measures of UV light exposure and risk of non-Hodgkin lymphoma. A high frequency of sun bathing and sunburns at age 20 years and 5-10 years before the interview and sun vacations abroad were associated with 30%-40% reduced risks of non-Hodgkin lymphoma (e.g., for sunbathing four times a week or more at age 20 versus never sunbathing, OR = 0.7, 95% CI = 0.6 to 0.9; for two or more sunburns a year at age 20 versus no sunburns, OR = 0.6, 95% CI = 0.5 to 0.8). These inverse associations increased in strength with increasing levels of exposure (all P(trend)< or =.01). Similar, albeit weaker, associations were observed for Hodgkin lymphoma. There were no clear differences among non-Hodgkin lymphoma subtypes, although associations were stronger for B-cell than for T-cell lymphomas. A history of skin cancer was associated with a doubling in risks of both non-Hodgkin and Hodgkin lymphoma.
  
  
  CONCLUSIONS
  A history of high UV exposure was associated with reduced risk of non-Hodgkin lymphoma. The positive association between skin cancer and malignant lymphomas is, therefore, unlikely to be mediated by UV exposure.
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Box 281, SE-171 77 Stockholm, Sweden. karin.ekstrom@meb.ki.se
authors.forename: Karin Ekström
authors.initials: KE
authors.lastname: Smedby
authors.forename: Henrik
authors.initials: H
authors.lastname: Hjalgrim
authors.forename: Mads
authors.initials: M
authors.lastname: Melbye
authors.forename: Anna
authors.initials: A
authors.lastname: Torrång
authors.forename: Klaus
authors.initials: K
authors.lastname: Rostgaard
authors.forename: Lars
authors.initials: L
authors.lastname: Munksgaard
authors.forename: Johanna
authors.initials: J
authors.lastname: Adami
authors.forename: Mads
authors.initials: M
authors.lastname: Hansen
authors.forename: Anna
authors.initials: A
authors.lastname: Porwit-MacDonald
authors.forename: Bjarne Anker
authors.initials: BA
authors.lastname: Jensen
authors.forename: Göran
authors.initials: G
authors.lastname: Roos
authors.forename: Bjarne Bach
authors.initials: BB
authors.lastname: Pedersen
authors.forename: Christer
authors.initials: C
authors.lastname: Sundström
authors.forename: Bengt
authors.initials: B
authors.lastname: Glimelius
authors.forename: Hans-Olov
authors.initials: HO
authors.lastname: Adami
mesh_terms: D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D016001:Confidence Intervals; D015986:Confounding Factors, Epidemiologic; D003718:Denmark / Q000453:epidemiology; D005260:Female; D006689:Hodgkin Disease / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000453:epidemiology; D016015:Logistic Models; D008223:Lymphoma / Q000453:epidemiology* / Q000209:etiology; D008228:Lymphoma, Non-Hodgkin / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D016017:Odds Ratio; D018570:Risk Assessment; D012307:Risk Factors; D011795:Surveys and Questionnaires; D013548:Sweden / Q000453:epidemiology; D014466:Ultraviolet Rays / Q000009:adverse effects