The link between ADHD and gut health: what we know so far

ADHD isn’t just about the brain. Growing research suggests the gut may play a surprising role too. From microbial imbalances to inflammation and nutrient absorption, the gut-brain axis could be a key piece of the puzzle. Here’s what the science says so far.

What is ADHD?

You may have heard of ADHD (Attention-Deficit Hyperactivity Disorder) – it is a neurodevelopmental disorder, with symptoms commonly developing between 3 to 6 years old. It’s characterised by ongoing symptoms of inattention, hyperactivity and impulsivity. This can show up in ways such as frequently losing everyday items, fidgeting or squirming while seated or interrupting others in games and meetings.¹

There is no complete consensus on the cause of ADHD, with scientists widely believing it to be a complex combination of environmental and genetic factors.² This is supported by research showing that children of parents with ADHD may have up to a 40% chance of developing the disorder.³

Where does ADHD begin?

ADHD symptoms begin in the brain 🧠- people with ADHD have differences in brain chemistry compared with those who don’t. Experts believe that dysfunction within the dopamine pathway leads to lower levels of dopamine and norepinephrine in the brain. The structure of the brain can also differ in those with ADHD, with alterations observed in the frontal cortex, limbic regions and basal ganglia, contributing to ADHD symptoms.⁴

The more we research the gut microbiome, the more we see just how much it may influence our physical and mental health and wellbeing. While the link between ADHD and the microbiome is still being investigated, researchers have found differences in the gut health of those with ADHD and those without.

Curious about the ADHD-gut connection? Read on to find out what the latest research is revealing.

An altered microbiome: the difference between those with ADHD and those without

Gut dysbiosis

Gut dysbiosis is an imbalance in the gut microbiome that leads to negative health outcomes. We talk a lot about gut dysbiosis here at CG, as your gut is your “second brain”. It plays a vital role in overall mood and mental and physical health. A combination of reduced microbial diversity, loss of beneficial bacteria and overgrowth of harmful bacteria leads to gut dysbiosis.

Variations in microbial abundance, richness and diversity have been observed in a range of neuropsychiatric conditions such as ADHD, depression and ASD amongst others. Research shows that individuals with ADHD have lower gut microbiota diversity than healthy controls.⁵

One study showed a higher prevalence of Blautia (genus), Anaerostipes (genus) and Lachnospiraceae (family) in the ADHD group when compared with the control group. Conversely, the prevalence of Verrucomicrobia (phylum), Akkermansia, Anaerococcus (genera), Christensenellaceae and Ruminococcaceae (family) were found to be significantly higher in the control group, than the ADHD cohort.⁶

Another study showed an increase of Odoribacter and Eggerthella and a decrease in Faecalibacterium (part of the Ruminococcaceae family) in those with ADHD.⁷

The mechanisms behind how these specific changes in microbial diversity affect symptoms and treatment are still being explored. But studies like these highlight just how powerful our gut bugs may be in influencing us – in ways we hadn’t previously imagined.

Low levels of short chain fatty acids (SCFAs)

SCFAs are by-products from the fermentation of dietary fibre by intestinal pr obiotic bacteria.⁸ These are also known as postbiotics. We look at these in our Microbiome Test as they play such a positive role in human health. SCFAs are important for modulating the immune system, maintaining the integrity of the gut barrier and have anti-inflammatory effects.⁹ They have also been shown to influence neurotransmitter production, especially serotonin and norepinephrine, which play a vital role in the mechanism of ADHD. ¹⁰

One study found that there was a significant decrease in the levels of SCFAs such as acetic, propionic, isobutyric, isovaleric and valeric acids in those with ADHD when compared to the control group. The researchers noted however, that there was no significant difference in the level of butyric acid between the two groups.¹¹

With decreased microbiome diversity and gut dysbiosis, it makes sense that people with ADHD may also have reduced SCFAs as a result. Good levels of probiotic bacteria such as Bifidobacterium, Faecalibacterium or Rosburia are needed to produce SCFAs.

The gut-brain axis: potential mechanisms linking ADHD to gut health

The gut-brain axis refers to the bidirectional communication pathway along the vagus nerve linking your brain with peripheral intestinal functions.¹² The microbes in your gut can send signals to the brain, influencing mood, perception and behaviour.¹³

From the research we can see that there does appear to be differences in the microbial diversity and a decrease of SCFAs in those with ADHD when compared with controls. This gives people with ADHD an increased risk of gut dysbiosis – which can have a knock on effect on symptoms.

Lower levels of SCFAs and gut dysbiosis can contribute to higher levels of inflammation in the gut, this can lead to high levels of pro-inflammatory cytokines. These cytokines cross the blood-brain-barrier, causing neuroinflammation and further disrupting neurotransmitter pathways, leading to ADHD symptoms.¹⁴

Implications for ADHD treatment

With alterations observed in the gut microbiome, the integration of gut-based interventions to support ADHD symptoms may be closer than you think! Research into synbiotics (prebiotics + probiotics) showed lower intestinal inflammation and increase in SCFAs in children with ADHD when given a synbiotic supplement. Supplementation with Lacobacillus rhamnosus GG in children with ADHD showed an improvement in emotional, physical, social and academic functioning when compared to the placebo group.¹⁵ Could probiotics, or synbiotics, be another tool to help manage ADHD symptoms?

However, there has been a mix in results – with some studies showing no differences between probiotic use and placebos as a treatment for ADHD symptoms.¹⁶ These studies use different probiotic strains, doses and durations, and we can’t forget that ADHD is a diverse condition, so a one-size-fits-all approach may not be suitable.

Although the research doesn’t show evidence of a cure, supporting gut health through a balanced, fibre-rich diet, alongside prebiotics and probiotics, just may be another piece of the puzzle for ADHD symptom management. Scientists have only just scratched the surface in looking into how the gut microbiome may play a part in neuropsychiatric conditions such as ADHD. While more research is needed, exploring the gut microbiome link may pave the way for integrative approaches to help individuals with ADHD.

Want to learn more about neurodiversity and the gut-brain connection ? Check out our article World Autism Month: how holistic care can empower individuals.

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