title: Suicide risk in relation to air pollen counts: a study based on data from Danish registers.
abstract: OBJECTIVE
  Since the well-observed spring peak of suicide incidents coincides with the peak of seasonal aeroallergens as tree-pollen, we want to document an association between suicide and pollen exposure with empirical data from Denmark.
  
  
  METHODS
  Ecological time series study.
  
  
  METHODS
  Data on suicide incidents, air pollen counts and meteorological status were retrieved from Danish registries.
  
  
  METHODS
  13 700 suicide incidents over 1304 consecutive weeks were obtained from two large areas covering 2.86 million residents.
  
  
  METHODS
  Risk of suicide associated with pollen concentration was assessed using a time series Poisson-generalised additive model.
  
  
  RESULTS
  We noted a significant association between suicide risk and air pollen counts. A change of pollen counts levels from 0 to '10-<30' grains/m(3) air was associated with a relative risk of 1.064, that is, a 6.4% increase in weekly number of suicides in the population, and from 0 to '30-100' grains, a relative risk of 1.132. The observed association remained significant after controlling for effects of region, calendar time, temperature, cloud cover and humidity. Meanwhile, we observed a significant sex difference that suicide risk in men started to rise when there was a small increase of air pollen, while the risk in women started to rise until pollen grains reached a certain level. High levels of pollen had slightly stronger effect on risk of suicide in individuals with mood disorder than those without the disorder.
  
  
  CONCLUSIONS
  The observed association between suicide risk and air pollen counts supports the hypothesis that aeroallergens, acting as immune triggers, may precipitate suicide.
authors.affiliation: National Centre for Register-based Research, Aarhus University, Denmark.
authors.forename: Ping
authors.initials: P
authors.lastname: Qin
authors.forename: Berit L
authors.initials: BL
authors.lastname: Waltoft
authors.forename: Preben B
authors.initials: PB
authors.lastname: Mortensen
authors.forename: Teodor T
authors.initials: TT
authors.lastname: Postolache
keywords: Epidemiology; Immunology; Public Health; Tropical Medicine