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  • Genetics, brain chemicals, and gut health are all linked to ADHD development.
  • New research has explored how the gut mycobiome may influence the condition.
  • Levels of three specific fungi were different among ADHD patients.
  • An unbalanced gut microbiome can lead to inflammation, which could contribute to mental health concerns.
  • Research is ongoing into how gut health and ADHD are related.

Around 6 million or 10% of children aged 3-17 in the US are diagnosed with attention-deficit/hyperactivity disorder (ADHD).

Several factors are thought to contribute to its onset and symptom severity, including the balance of bacteria in the gut microbiome.

Now, new research published April 5 from scientists in Taiwan, published in The Journal of Child Psychology and Psychiatry, has gone one step further to explore the association between gut health and ADHD.

They focused on the mycobiome, which encompasses the fungi housed in the microbiome — and found that imbalances of certain fungi were more prevalent in ADHD patients.

Using high-throughput sequencing, the researchers analyzed DNA from the stool samples of 70 individuals: 35 ADHD patients and 35 controls.

They found that levels of certain fungi were different between the two groups. Compared to the control group, those with ADHD had higher amounts of Ascomycota and significantly lower amounts of Basidiomycota in their gut mycobiome.

But they were not the only differences seen. Those with ADHD had significantly more Candida (particularly Candida albicans).

A second element of the study involved in vitro testing (performed outside of a living organism) and found that Candida albicans greatly increased the permeability of the gut lining.

A more permeable gut lining can lead to concerns such as inflammation.

The findings are significant, said Jordan Haworth, a gastrointestinal physiologist at the Functional Gut Clinic in Manchester, UK, who was not involved with the research.

“This is one of the first studies to sequence the mycobiome in healthy controls and people with ADHD,” he told Healthline.

“Gut fungi are an important part of the gut microbiome, and there are hundreds of different fungi living in the gut,” revealed Dr. Sarah Cooke, a UK-based general practitioner specializing in nutrition.

“The types and proportions of fungi can be affected by multiple factors,” she told Healthline. “These include ethnicity, lifestyle, medication use, type of diet, and how regularly one may brush their teeth [as Candida albicans can thrive in the mouth].”

In this study, three fungi were highlighted as being of ‘abnormal’ levels in ADHD patients. With regards to Ascomycota and Basidiomycota, their specific function is not entirely clear, said Haworth.

“These fungi aren’t necessarily novel, but they’re not something other people have really looked at,” he explained. “There’s not a lot of research around what their potential mechanism could be.”

Fortunately, scientists have a much better understanding of Candida.

“Candida, in general, are a genus of yeasts—and they’re the most frequently detected kind of fungi in human feces,” Haworth shared. “In normal health, Candida albicans are pretty harmless. But if your health is compromised, this yeast can flourish and become more detrimental.”

Medications like antibiotics and immunosuppressants can deplete the gut’s ‘good’ bacteria and allow yeast to thrive. Unfortunately, Haworth said, “whether ADHD medications can disrupt the gut microbiome isn’t something that’s really been looked into.”

As found during the in vitro testing, flourishing Candida albicans may contribute to gut permeability—which can lead to inflammation.

“The intestinal barrier has two main jobs,” said Haworth. “The first is to absorb nutrients, and the second is to prevent unwanted things in the gut from entering the body—mainly microbes and their waste products.”

This barrier is made up of cells that are packed tightly together by proteins, he explained. However, when these proteins are damaged by inflammation, the gaps between the cells become bigger.

The gaps allow metabolites and toxins to enter the bloodstream, said Haworth, and “travel through the body to different sites and cause inflammation.”

“The gut-brain axis is an important pathway where transmissions occur,” Cooke added. “Gut permeability may affect these transmissions connecting the gut and the brain.”

It’s also worth noting that previous studies have revealed that imbalanced gut microbiota can trigger an immune response that also leads to inflammation.

It’s not entirely clear how inflammation and ADHD are linked, shared Sarah-Nicole Bostan, Ph.D., a clinical health psychologist and director of behavior change strategy at Signos.

“The study of gut-brain interactions is still in its infancy as it relates to functional impairment from mental health symptoms,” she told Healthline, “[although] the relationship is increasingly acknowledged.”

There are currently various hypotheses on the ADHD-inflammation relationship.

One, for instance, relates to the protective layer around the brain. “Just like the gut, the brain has a barrier, called the blood-brain barrier,” Haworth explained. “This prevents unwanted things from the blood entering the brain.”

However, he continued, “we know from studies that increased intestinal permeability is closely linked to a disrupted blood-brain barrier—[although] we can’t be sure what’s causing it.”

Another potential factor, said Haworth, involves the kynurenine pathway. In the gut, microbes work to convert an amino acid called tryptophan into the neurotransmitter serotonin.

But “some pathogenic microbes, including yeast species, don’t convert tryptophan into serotonin,” he said. “Instead, they convert it into something called kynurenine. And these can cross the blood-brain barrier and trigger neuroinflammation.”

The kynurenine pathway, Haworth added, is notably more responsive in those with mental health concerns such as ADHD, depression, and schizophrenia.

Meanwhile, Cooke explained that some brain inflammation is beneficial. But adverse effects can arise when inflammation occurs over an extended duration.

“Neuroinflammation (inflammation of the brain) has a primary function of protecting the brain against pathogens (disease-causing organisms) via a process which encourages tissues to repair themselves,” she said.

“However, if the inflammatory state is prolonged, then the inflammation can become detrimental and stop the renewal of cells,” Cooke continued.

“Neuroinflammation has been proposed in contributing to the development of ADHD, and it is noted that a high proportion of patients with ADHD also have a co-existing inflammatory or autoimmune condition.”

If an off-kilter gut microbiome and mycobiome play a role in ADHD, does that mean getting things balanced will ease symptoms?

Potentially, said Dr. Raphael Wald, a neuropsychologist at Marcus Neuroscience Institute, part of Baptist Health. “I would anticipate an improvement in ADHD symptoms with a more balanced gut microbiome,” he told Healthline.

Bostan noted that “because the gut mycobiome and microbiome are influenced heavily by diet and environment, it follows that changing diet and environment would also change gut mycobiome and microbiome composition.”

“However,” she continued, “it’s unclear how and to what degree this would impact ADHD symptoms.”

Some studies into whether probiotics (food for ‘good’ gut bacteria) can aid in easing ADHD symptoms have shown potentially positive results—although more clinical studies are needed.

Either way, a happy and healthy gut is vital for mental and physical wellbeing. Numerous approaches can help rebalance and nourish the beneficial bacteria and fungi in your gut, said Jenna Hope, a registered nutritionist in the UK.

She shared with Healthline that these include:

  • Consuming a varied, plant-based diet
  • Consuming foods containing prebiotics and probiotics—such as onions, garlic, leeks, bananas, yogurt (containing live cultures), sourdough bread, and fermented vegetables
  • Limiting high-sugar foods where possible
  • Replace refined grains with whole grains (as these provide dietary fiber, which acts as food for good bacteria)
  • Managing stress
  • Prioritizing sleep
  • Exercising in moderation

Although the gut microbiome and mycobiome have been linked to ADHD, other factors are believed to contribute to its development and symptom severity.

“Onset of any mental health challenge, including ADHD, is often multifactorial—meaning there are multiple pathways which influence development,” said Bostan.

According to Wald, three other common determinants are:

  • Genetics
  • Anatomy (the volume of different structures of the brain)
  • Physiology (the action of chemical messengers in the brain)

“Unfortunately, it is not possible to point to one single difference found in people with ADHD,” Wald concluded.