If you thought cat litter and juvenile concussions sounded like improbable causes of suicide, here is another one for you: researchers from Aarhus University have identified pollen as a potential explanation for the seasonal effects on suicide rates (April is apparently the cruelest month).

Statistical significance only goes so far
A study published in the journal BMJ Open shows an apparent correlation between the number of suicides in Denmark and the amount of pollen in the air.

“We were excited to see the positive results. But it is also important to note that, although we found a statistically significant correlation between the amount of pollen and the number of suicides in the population, the effect was not huge," says Ping Qin, associate professor at the National Center for Register-based Research and head of the study.

Furthermore, the effect of the pollen was found to be strongest on people who already had mood disorders or were diagnosed with depression.

Puzzling mechanism
Although the exact cause of the apparent phenomenon is not known, the study hypothesises that pollen might trigger an allergic inflammatory condition, which sets in motion signalling molecules called cytokines which affect people who are prone to mood swings.

Suicide on the rise
Suicide is a rising cause of death. According to Health Metrics and Evaluation's Global Burden of Disease 2010, in the developed world, suicide became the leading cause of death in 2010 for people aged 15 to 49.