Those who had a pet dog in their first 12 years were up to 24 percent less likely to have schizophrenia.
But it didn't protect against bipolar disorder—and the pet cat didn't have any impact on either problem, say researchers at the Johns Hopkins Children's Center. They had questioned a group of 1,371 people aged between 18 and 65—396 of whom had schizophrenia, 381 were bipolar, and the rest didn't have any mental health issues—about having a pet dog or cat growing up. The greatest protection seemed to be between birth and the age of three, although the researchers said there was a positive effect up to the age of 12.
The researchers don't really know why having a dog has such a positive impact on mental health, but they think it may have a physical cause, with perhaps something in a dog's microbiome bolstering the immune system in people that protects them against psychiatric disorders.
Whatever the reason, it could mean that 840,000 cases of schizophrenia in the US—that's 24 percent of the 3.5 million sufferers—might never have happened if there had been a dog in the family home.