section_path: Risk factors/Environmental exposures
section_name: Environmental exposures
paragraph_text: Environmental exposures
  
  Some environmental exposures, including air pollution, intense sunlight, sunlight duration, hot weather, and high altitude, are associated with suicide. There is a possible association between short-term PM exposure and suicide. These factors might affect certain high-risk individuals more than others.
  
  The time of year may also affect suicide rates. There appears to be a decrease around Christmas, but an increase in rates during spring and summer, which might be related to exposure to sunshine. Another study found that the risk may be greater for males on their birthday.
  
  Genetics might influence rates of suicide. A family history of suicide, especially in the mother, affects children more than adolescents or adults. Adoption studies have shown that this is the case for biological relatives, but not adopted relatives. This makes familial risk factors unlikely to be due to imitation. Once mental disorders are accounted for, the estimated heritability rate is 36% for suicidal ideation and 17% for suicide attempts. An evolutionary explanation for suicide is that it may improve inclusive fitness. This may occur if the person dying by suicide cannot have more children and takes resources away from relatives by staying alive. An objection to this explanation is that deaths by healthy adolescents likely do not increase inclusive fitness. Adaptation to a very different ancestral environment may be maladaptive in the current one.