Having a dog as a child could cut your risk of getting schizophrenia, a study has suggested.
Researchers found adults who owned a dog before they were 13 were 24 per cent less likely to have the mental health disorder.
Scientists believe humans may catch bugs from dogs which bolster their immune system and gut bacteria, and playing with them can reduce stress.
Both factors are thought to play a role in the development of schizophrenia – but there is no clear cause.
The study of 1,300 adults, however, found having a pet cat as a child offered little benefit, and may even have the opposite effect.
Having a dog in childhood could cut the risk of developing schizophrenia as an adults by 24 per cent, a study has suggested
Professor Robert Yolken and team at Johns Hopkins Children’s Center, Baltimore, published their findings in the journal PLOS ONE.
Professor Yolken said: ‘Serious psychiatric disorders have been associated with alterations in the immune system linked to environmental exposures in early life.
‘And since household pets are often among the first things with which children have close contact, it was logical for us to explore the possibilities of a connection between the two.’
A total of 1,371 men and women between the ages of 18 and 65 were included in the study.
Some 396 people had schizophrenia, 381 had bipolar disorder, and 594 had never been diagnosed with a psychiatric disorder.
All participants were asked if they had a household pet cat or dog or both during their first 12 years of their lives.
Professor Yolken estimated some 840,000 cases of schizophrenia could have been prevented by having a dog in the house as a child.
He calculated this using figures that show 3.5million people have been diagnosed with the disorder in the US.
‘The largest apparent protective effect was found for children who had a household pet dog at birth or were first exposed after birth but before age three,’ Professor Yolken said.
The exact cause of schizophrenia is unknown, but a combination of genetic and environmental factors is likely to be involved.
If someone is more vulnerable to developing schizophrenia, a stressful life event or drug misuse, for example, could trigger the disorder.
Dogs may protect a person from the risk of schizophrenia in a number of ‘several plausible’ reasons, the researchers said.
It’s well known petting a dog helps reduce stress. This may keep inflammation, and therefore the immune system response, at bay.
This is a risk for developing psychiatric disorders if an immune system is overactive, the researchers said.
A dog can also transfer bacteria to the owner, which may, in theory, boost the gut microbiome of children.
Schizophrenia has been shown to be connected to the gut, although scientists have yet to produce concrete evidence.
The findings show owning a pet had no protective effect, or negative risk, for bipolar disorder.
People who had owned cats as children didn’t have a change in risk of developing schizophrenia or bipolar disorder.
‘However, we did find a slightly increased risk of developing both disorders for those who were first in contact with cats between the ages of 9 and 12,’ Professor Yolken said.
It’s not the first time cats have been linked to schizophrenia.
Cats carry Toxoplasma gondii (T. gondii), a parasite which has been found to raise the risk of developing schizophrenia by 50 per cent. It can be spread to people through contact with cat litter trays and uncooked meat.
Professor Yolken said: ‘A better understanding of the mechanisms underlying the associations between pet exposure and psychiatric disorders would allow us to develop appropriate prevention and treatment strategies.’