(CNN)-- Owning a cat might increase a woman's risk for attempting suicide, new research suggests.
A new study from the July 2 issue of Archives of General Psychiatry showed that women infected with the Toxoplasma gondii parasite found in some cats' feces were 1.5 times more likely to try to take their own life than those who were not infected.
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"We can't say with certainty that T. gondii caused the women to try to kill themselves, but we did find a predictive association between the infection and suicide attempts later in life that warrants additional studies," study author Dr. Teodor T. Postolache, associate professor of psychiatry and director of the Mood and Anxiety Program at the University of Maryland School of Medicine, said in a written statement.
For the study, researchers looked at nearly 46,000 Danish women who gave birth between 1992 and 1995 and whose babies were screened for T. gondii antibodies. Babies don't typically produce antibodies to the parasite until three months after their birth, thus newborns with antibodies suggest their moms were infected by the parasite. The researchers then cross-referenced Danish health registries to see if any of these women later attempted suicide in the decades since, and then looked at a psychiatric health register to determine which of these women were previously diagnosed with mental illness.
The researchers found an increase in suicide risk for women that corresponded with the levels of parasite antibodies found in the children's blood tests. Seventy-eight women had a violent suicide attempt, which may have involved guns, sharp instruments or jumping from high places, which suggests an 81 percent risk increase for infected women. More than 500 women in the study attempted suicide, so the overall actual risk was still small.
About one-third of the world's population is thought to be infected with the T. gondii parasite, which causes the infection toxoplasmosis. The parasite hides from the immune system in "cysts" found in brain and muscle cells and many people won't even show symptoms. The infection, however, may cause headache, fever, a mild illness similar to mononucleosis, muscle pain, blurred vision and seizures within two weeks. Toxoplasmosis has also been linked to mental illness such as schizophrenia and changes in behavior, the researchers said.
The parasite thrives in cats' intestines and is often passed through their feces into litter boxes or elsewhere in the home. As such, women are often warned not to change the litter box during pregnancy to reduce risk of infection. However the parasite can also be passed from other animals, or through contaminated drinking water, unwashed vegetables or by eating undercooked or raw meat.
Postolache notes his study had limitations, namely that the researchers didn't capture many occurrences of attempted suicide and weren't able to determine what caused the suicidal behavior.
"T. gondii infection is likely not a random event and it is conceivable that the results could be alternatively explained by people with psychiatric disturbances having a higher risk of becoming T. gondii infected prior to contact with the health system," Postolache said. The study also didn't look at men and women who didn't have kids.
Dr. J. John Mann, an international suicide expert at Columbia University, said in press release that there's mounting evidence that immune factors may be tied to suicide risk, so identifying infections that can trigger a heightened immune system response in at-risk patients that may lead to new suicide prevention strategies.
About 1 million people commit suicide and another 10 million attempt suicide worldwide each year.