A common yeast infection could trigger schizophrenia and bipolar disorder, scientists have warned.
Their study found a link between a history of Candida infections – commonly known as thrush or candidiasis – and higher rates of the mental illnesses.
They found thrush was more common in a group of men with schizophrenia or bipolar disorder, than those without the infection.
And in women, the researchers noted those with the mental health conditions and who tested positive for Candida performed worse on a standard memory test than women with schizophrenia or bipolar disorder who had no evidence of past thrush infection.
Though the findings do not establish a direct cause and effect relationship, researchers say their investigations warrant a more detailed examination of the role of lifestyle, immune system weaknesses and connections between the gut and brain as contributing factors to the risk of psychiatric disorders and memory impairment.
Dr Emily Severance, assistant professor of pediatrics at Johns Hopkins University School of Medicine, said: ‘It’s far too early to single out Candida infection as a cause of mental illness or vice versa.
‘However, most Candida infections can be treated in their early stages, and clinicians should make it a point to look out for these infections in their patients with mental illness.’
She adds that Candida infections can also be prevented by decreased sugar intake and other dietary modifications, avoidance of unnecessary antibiotics, and improvement of hygiene.
Candida albicans is a yeast-like fungus naturally found in small amounts in human digestive tracts, but its overgrowth in warm, moist environments causes burning, itching symptoms, thrush (rashes in the throat or mouth) in infants and those with weakened immune systems, and sexually transmittable genital yeast infections in men and women.
In its more serious forms, it can enter the bloodstream. In most people, the body’s own healthy bacteria and functioning immune system prevent its overgrowth.
Dr Severance said her team focused on a possible association between Candida susceptibility and mental illness in the wake of new evidence suggesting that schizophrenia may be related to problems with the immune system, and because some people with weakened immune systems are more susceptible to fungal infections.
She added that patients and parents of patients had shared personal stories and testimonials with the researchers about their experience with yeast infections.
These discussions, Dr Severance said, prompted the investigation into possible links between mental illness and the microbiome – the body’s natural collection of bacteria.
The researchers, she added, chose to focus on Candida because it is one of the most common types of yeast in the body.
Researchers took blood samples from a group of 808 people between the ages of 18 and 65.
This group was composed of 277 controls without a history of mental disorder, 261 individuals with schizophrenia and 270 people with bipolar disorder.
They used the samples to measure the level of antibodies to Candida, which indicates a past infection with the yeast.
After they accounted for age, race, medications and socioeconomic status, which could skew the results, the researchers looked for patterns that suggested links between mental illness and infection rates.
Significantly, the team says, it found no connection between the presence of Candida antibodies and mental illness overall in the total group.
But when the investigators looked only at men, they found 26 per cent of those with schizophrenia had Candida antibodies, compared to 14 per cent of the control males.
There wasn’t any difference found in infection rate between women with schizophrenia (31.3 per cent) and controls (29.4 per cent).
The higher infection rate percentages in women over men likely reflects an increased susceptibility for this type of infection in all women.
Candida albicans, illustrated, is a yeast-like fungus naturally found in small amounts in human digestive tracts, but its overgrowth in warm, moist environments causes burning, itching symptoms, thrush in infants and those with weakened immune systems, and sexually transmittable genital yeast infections in men and women
Men with bipolar disorder had clear increases in Candida as well, with a 26.4 per cent infection rate, compared to only 14 per cent in male controls.
But, after accounting for additional variables related to lifestyle, the researchers found that the association between men with bipolar disorder and Candida infection could likely be attributed to homelessness.
However, the link between men with schizophrenia and Candida infection persisted and could not be explained by homelessness or other environmental factors.
Many people who are homeless are subjected to unpredictable changes in stress, sanitation and diet, which can lead to infections like those caused by Candida.
Dr Severance said the data adds support to the idea that environmental exposures related to lifestyle and immune system factors may be linked to schizophrenia and bipolar disorder, and that those factors may be different for each illness.
Similarly, specific mental illnesses and related symptoms may be very different in men versus women.
Dr Severance said: ‘Although we cannot demonstrate a direct link between Candida infection and physiological brain processes, our data show that some factor associated with Candida infection, and possibly the organism itself, plays a role in affecting the memory of women with schizophrenia and bipolar disorder, and this is an avenue that needs to be further explored.
‘Because Candida is a natural component of the human body microbiome, yeast overgrowth or infection in the digestive tract, for example, may disrupt the gut-brain axis.
‘This disruption in conjunction with an abnormally functioning immune system could collectively disturb those brain processes that are important for memory.’
Dr Severance said her team now plans to take their research of the gut-brain connection to test on mice models to look for a cause-and-effect relationship between Candida and memory deficits.
The findings are published online in npj Schizophrenia – a new publication from the Nature Publishing Group.