The relationship between the microbiota and ADHD in childhood and adolescence
In recent years, science has begun to rediscover the essential role played by the trillions of bacteria that inhabit our gut. What was once considered merely a matter of digestion is now understood as a complex system capable of influencing the brain , mood, and possibly attention deficit hyperactivity disorder (ADHD).
But what does the gut have to do with a neurodevelopmental disorder like ADHD? In this article, we explain what science says about the role of the gut microbiota in childhood ADHD , what mechanisms might be involved, and whether there are dietary treatment options, such as probiotics.
The gut microbiota: much more than digestion
The gut microbiota is the collection of microorganisms—primarily bacteria—that live in our digestive system, especially the colon. In a healthy person, these bacteria form a diverse and balanced community that participates in multiple functions: they aid in the digestion of certain foods, regulate the immune system, and synthesize certain vitamins and bioactive compounds that can influence other organs, including the brain.
During childhood, the gut microbiota is rapidly developing and is particularly sensitive to factors such as delivery method, breastfeeding, diet, and antibiotic use. Increasing scientific evidence suggests that an imbalance in the microbiota, known as dysbiosis, may influence neurological development and behavior in children.
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ADHD and its possible connection to the gut
ADHD is a complex neurodevelopmental disorder that affects approximately 5% of children and adolescents. Its origin is multifactorial: genetics plays a significant role, but environmental factors, such as diet, sleep, and exposure to certain substances, also have an influence. In recent years, several studies have explored whether the gut microbiota could also be another key piece in this complex puzzle.
Several studies have observed that the gut microbiota of children with ADHD often differs from that of children without the disorder . In particular, lower levels of beneficial bacteria such as Faecalibacterium have been detected, along with a greater presence of other species that could be linked to inflammatory processes or alterations in the production of certain neurotransmitters. Although these differences are not identical in all studies, the results consistently point to a distinct microbial pattern in many children with ADHD.
Now, the big question is: are these differences a cause of ADHD, or rather a consequence of the disorder?
Does the gut microbiota cause ADHD or is it merely affected by it?
In science, distinguishing between cause and effect is not always easy. The differences observed in the gut microbiota could be due to multiple factors associated with ADHD, such as diet, medication use (e.g., methylphenidate), stress, or certain lifestyle habits.
To investigate this question further, studies have been conducted using animal models. In one of these studies, the gut microbiota of children with ADHD was transplanted into mice that lacked their own gut bacteria. Surprisingly, the mice that received this microbiota developed brain changes and behaviors distinct from those that received microbiota from children without ADHD. These findings suggest that the gut microbiota could directly influence brain function and behavior .
Taking care of gut health through good nutrition and, in some cases, with the support of probiotics, could be a complementary strategy to improve the well-being of children with ADHD.
Other studies conducted on laboratory animals have shown that modifying the gut microbiota of mice with ADHD-like behaviors can reduce their symptoms. Furthermore, some genetic analyses in humans have identified certain bacteria whose presence appears to be associated with a higher or lower risk of developing ADHD, which would reinforce the hypothesis of a possible causal relationship .
Although we cannot yet say with complete certainty that the microbiota causes ADHD, current evidence suggests that it could play a relevant role in its appearance or evolution.
How can the gut influence the brain?
The connection between the gut and the brain is known as the gut-brain axis. It is a bidirectional communication pathway: the brain can influence the gut (for example, stress can disrupt digestion), but the gut can also send signals that affect the brain.
There are several ways in which this interaction occurs:
- Immune pathway: When the gut microbiota is imbalanced, it can increase intestinal permeability, allowing certain substances to pass into the bloodstream and activate the immune system. This can trigger low-grade inflammation that also affects the central nervous system.
- Nervous pathway: Some gut bacteria can stimulate the vagus nerve, a kind of "highway" that directly connects the gut to the brain. Through this pathway, signals can be sent that modulate brain activity.
- Metabolic pathway: Certain bacteria, such as Lactobacillus or Bifidobacterium, produce compounds like short-chain fatty acids, for example, butyrate or propionate. These metabolites have anti-inflammatory properties and can cross the blood-brain barrier, acting directly on the central nervous system.
- Neurotransmitter pathway: Some bacterial species collaborate in the production of precursors to key neurotransmitters such as dopamine and serotonin, which are implicated in ADHD. An imbalance in the microbiota could disrupt this delicate network of chemical communication.
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What if we modulate the microbiota? Therapeutic strategies
If the gut microbiota is involved in ADHD, can we intervene to improve symptoms? This is one of the most active lines of research today.
Probiotics
Probiotics are live microorganisms that, when administered in adequate amounts, provide health benefits. In the case of ADHD, research has focused particularly on strains of Lactobacillus and Bifidobacterium.
Some studies have observed that certain probiotics can improve mood, reduce anxiety, or promote better sleep in children and adolescents with ADHD. However, when analyzing the core symptoms of the disorder—such as inattention, hyperactivity, or impulsivity—the results are more modest. A recent meta-analysis concluded that probiotics, on their own, do not significantly reduce these symptoms , although they may offer additional benefits when used alongside standard medication.
Certain probiotics can improve mood, reduce anxiety, or promote better sleep in children and adolescents with ADHD, but the results on the core symptoms of the disorder are more modest.
One particularly interesting study administered probiotics to infants during their first six months of life and observed that, by age 13, none of them had developed ADHD, while 17% of the group that did not receive probiotics had. Although this is a single study and its results need to be confirmed, it opens a promising line of research into ADHD prevention from early developmental stages.
Prebiotics, synbiotics and dietary fiber
Prebiotics are components found in some foods, usually dietary fiber, that serve as food for beneficial bacteria in the gut. When combined with probiotics, they form what are called synbiotics, which have a dual purpose: to repopulate the gut with healthy microorganisms and, at the same time, provide them with the nutrient-rich environment they need to thrive.
In a clinical trial conducted in children with ADHD, the administration of a synbiotic did not produce significant improvements in the disorder's main symptoms . However, a reduction in inflammation and an increase in beneficial intestinal metabolites were observed, suggesting that this type of intervention may be generating positive effects at a biological level, even if these take longer to translate into visible clinical changes.
In this sense, following a diet rich in fruits, vegetables, legumes and whole grains, which are natural sources of dietary fiber, can be a simple and effective way to promote a healthy gut microbiota from childhood.
Mediterranean and anti-inflammatory diet
Beyond supplements, what we eat daily has a profound impact on our gut and brain health. The Mediterranean diet, rich in fruits, vegetables, legumes, whole grains, oily fish, nuts, and extra virgin olive oil, has been associated with numerous health benefits , including a lower risk of neurodevelopmental disorders.
Several observational studies have found that children with ADHD tend to follow less healthy eating patterns, with higher consumption of ultra-processed foods, sugary drinks, and pastries, and lower intake of fresh, fiber-rich foods. Conversely, children who adhere more closely to the Mediterranean diet exhibit fewer symptoms of inattention and hyperactivity, as well as a lower risk of being diagnosed with ADHD.
The Mediterranean diet has been associated with numerous health benefits, including a lower risk of neurodevelopmental disorders.
Although these studies do not demonstrate a direct causal relationship, they do suggest that a balanced and anti-inflammatory diet, such as the Mediterranean diet which is also rich in dietary fiber, could act as a protective factor against the development of the disorder, or help to modulate its evolution.
What can we do at home? Practical recommendations
Although there is no specific treatment for ADHD based on modulating the gut microbiota, there are several everyday actions that can contribute to maintaining gut health and promoting proper neurological development:
- Promote a diet rich in fiber, including daily fruits, vegetables, legumes and whole grains.
- Reduce or limit the consumption of ultra-processed foods, sugary drinks, and sweets.
- Incorporate fermented foods such as yogurt, kefir or sauerkraut.
- Avoid unnecessary use of antibiotics, as they alter the intestinal microbiota.
- Promote a healthy lifestyle: adequate rest and sleep, regular exercise, and stress management.
And, of course, remember that ADHD treatment must be comprehensive . Interventions targeting the gut microbiota can be a useful complement, but they do not replace medication, psychological therapy, or educational support when indicated.
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Conclusion: a new piece in the ADHD puzzle
The gut and brain are far more connected than we previously thought. The gut microbiota is emerging as a key player in neurological development and may be involved in disorders such as ADHD. While we still lack conclusive evidence that modulating it can alter the course of the disorder, current findings are promising.
Maintaining gut health through a good diet and, in some cases, with the support of probiotics, could be a complementary strategy to improve the well-being of children with ADHD . We will continue to learn in the coming years, but in the meantime, we already have enough reasons to look at the gut with a new perspective.
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