title: Does incidence of breast cancer and prostate cancer decrease with increasing degree of visual impairment.
abstract: OBJECTIVE
  The issue of light at night and cancer continuously attracts discussion. The major hypotheses are that melatonin may decrease risk of hormone-related cancers, particularly breast cancer, or even act as a potent antioxidant and thus have a protective effect against cancer development in general.
  
  
  METHODS
  We tested the hypothesis that blind persons are at lower risk of cancer in a follow-up study linking a cohort of 17,557 persons with visual impairment identified from the Finnish Register of Visual Impairment with cancer incidence data of the Finnish Cancer Registry for years 1983-2003.
  
  
  RESULTS
  Breast cancer risk in females decreased by degree of visual impairment, and a similar but less consistent trend was observed for prostate cancer in males. The incidence for the remaining cancers among nearly to totally blind persons was significantly higher than in average Finnish population.
  
  
  CONCLUSIONS
  Our findings add to the suggestive epidemiological evidence for a decreased risk of hormone-related cancers in people with visual impairment and, consequently, a relationship between visible light at night and breast cancer risk. The result is strongly against the hypothesis of a systemic protective effect related lack of visible light.
authors.affiliation: Finnish Cancer Registry, Institute for Statistical and Epidemiological Cancer Research, Liisankatu 21B, Helsinki, FIN-00170, Finland. eero.pukkala@cancer.fi
authors.forename: Eero
authors.initials: E
authors.lastname: Pukkala
authors.forename: Matti
authors.initials: M
authors.lastname: Ojamo
authors.forename: Sirkka-Liisa
authors.initials: SL
authors.lastname: Rudanko
authors.forename: Richard G
authors.initials: RG
authors.lastname: Stevens
authors.forename: Pia K
authors.initials: PK
authors.lastname: Verkasalo
mesh_terms: D001766:Blindness / Q000503:physiopathology; D001943:Breast Neoplasms / Q000453:epidemiology / Q000503:physiopathology*; D005260:Female; D006801:Humans; D015994:Incidence; D008027:Light; D008297:Male; D008875:Middle Aged; D011471:Prostatic Neoplasms / Q000453:epidemiology / Q000503:physiopathology*; D015354:Vision, Low / Q000503:physiopathology*