Yeast infections have been linked to schizophrenia and bipolar disorder in a new study, leading researchers to suggest that infections like thrush could be an early sign of mental illness.
Researchers found significantly higher exposure to Candida albicans, which can cause thrush, among males with schizophrenia and bipolar disorder.
This association was weaker among women, however high Candida albicans exposure was also linked with reduced mental function in females with schizophrenia.
The study's authors suggest that doctors should screen for yeast infections alongside schizophrenia and bipolar disorder.
They also believe that exposure to this particular yeast infection could "be a formative step in the development of schizophrenia".
A team of researchers from the Johns Hopkins University School of Medicine measured IgG antibody levels to determine lifetime exposure to Candida albicans, which causes yeast infections such as thrush in humans.
For the study, which was published in npj Schizophrenia, researchers took blood samples from a group of 808 people between the ages of 18 and 65.
This group was composed of 277 people without a history of mental disorder, 261 individuals with schizophrenia and 270 people with bipolar disorder.
The researchers used the blood samples to quantify the amount of IgG class antibodies to Candida, which indicates a past infection with the yeast.
After accounting for factors like age, race, medications and socioeconomic status, they looked for patterns that suggested links between mental illness and infection rates.
They found that a history of thrush was more common in men with schizophrenia and bipolar disorder, compared to those without a mental illness.
The link was weaker among women, however in those females who had schizophrenia, a history of thrush was associated with reduced mental function.
Co-author 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."
Researchers said their findings do not establish a cause-and-effect relationship between mental illness and yeast infections.
But they did add that it should prompt a more detailed examination into the role of lifestyle, immune system weaknesses and gut-brain connections as contributing factors to the risk of psychiatric disorders and memory impairment.
Commenting on the study, Dr Helen Webberley, the dedicated GP for Oxford Online Pharmacy, said: "We need to be very careful about drawing any conclusions from this study as there was no significant positive finding overall.
"It is an interesting thought and may merit further investigation, but it's worth bearing in mind that the yeasts that lead to thrush live as a commensal in many women and men.
"Certainly in my clinical practice, I have seen no evidence of any cause and effect between mental illness and this common yeast infection."
Vaginal thrush is a common yeast infection which affects most women at some point in their lives.
While many people with thrush experience no symptoms at all, others can experience itching and soreness around the entrance of the vagina, pain on sexual intercourse and vaginal discharge, which is usually odourless and may be thick and white or thin and watery.
"Thrush can usually be treated with anti-fungal medication which can be taken orally, in capsule form, as a pessary inserted into the vagina, or through the use of an intravaginal cream," explains Dr Webberley.
"There are certain triggers which can cause an increase in vaginal yeast which leads to thrush, such as the use of perfumed products in intimate areas, stress and high sugar foods.
"Avoiding such triggers can help reduce the chances of thrush developing."
She continued: "If you are concerned, visit your GP. Alternatively, kits which test for common infections such as thrush are available online and can be easily carried out in the comfort and discretion of your own home."