ADHD

The Gut Link to Attention and Reward

Researchers are still early in exploring this connection, and the studies are small. What makes them worth reading is that one of them followed a specific chain from a bacterial gene to brain activity, rather than stopping at a list of bacteria. Attention deficit hyperactivity disorder involves difficulty sustaining attention, restlessness and impulsivity. A blunted response to anticipating a reward is one of its recognised features, and that is where the gut evidence lands.

From a bacterial gene to a brain scan

Researchers compared gut bacteria in 19 people with ADHD against 77 without it. Several bacterial groups differed, though only marginally.

Rather than stop there, the team predicted what the bacteria present could do. They focused on genes involved in making phenylalanine, tyrosine and tryptophan. These are amino acids the body uses as raw material for dopamine, noradrenaline and serotonin, the chemical messengers most involved in attention and reward.

One enzyme stood out. Cyclohexadienyl dehydratase, which helps build phenylalanine, was predicted to be about 150% more abundant in the ADHD group.

Then came the part that connects the gut to the brain. In 28 participants who had brain scans, higher levels of that enzyme were associated with a weaker response in the ventral striatum while they anticipated a reward. The ventral striatum is a region central to motivation.

That association held regardless of whether the person had an ADHD diagnosis, which suggests the enzyme relates to the brain response itself rather than to the label.

Source: Gut microbiome in ADHD and its relation to neural reward anticipation

Evidence that starts in infancy

If gut bacteria matter here, the effect might begin long before a diagnosis. Two studies have looked.

One followed infants and recorded who later developed ADHD or a related condition. Babies with higher levels of Bifidobacterium in early life had a lower risk.

A later birth cohort study tracked children to age 10. Those who developed ADHD had a different gut community at six months old, notably short of lactic acid bacteria such as the Lactobacillales.

Now hold that against the previous section, because the two do not agree. The adolescent and adult study found Bifidobacterium raised in ADHD. The infant study found low Bifidobacterium associated with higher later risk.

Both cannot be a simple description of the same thing. The most likely explanations are that timing matters, that Bifidobacterium covers many species doing different jobs, or that one of the findings will not replicate. Either way, it's early work, and worth reading as such.

Source: A narrative review of research advances in gut microbiota and microecological agents in children with attention deficit hyperactivity disorder (ADHD)

Why the amino acid route is still worth attention

Despite the disagreement, one thread holds up, and it is the mechanism rather than the specific bacteria.

Phenylalanine, tyrosine and tryptophan cannot all be made by the human body. They arrive in food, are absorbed in the intestine, and gut bacteria both produce and consume them. So bacteria sit directly on the supply line for the raw materials of dopamine and serotonin.

That is established biology, independent of any ADHD study. What remains unproven is how much the bacterial contribution actually shifts what reaches the brain, given that diet supplies these amino acids in far larger quantities.

The honest position is that the route exists and its importance is unmeasured.

What this means for you

ADHD is assessed and treated by a specialist, and medication and behavioural support are the treatments with the strongest evidence behind them. In addition, the work above places gut bacteria on the supply line for the raw materials of dopamine and serotonin, though it's early and points in more than one direction. A varied, plant-rich diet supports the same gut bacteria sitting on that supply line. That's the same idea behind GutLab, everyday gut health starts with regularly feeding the microbiome a broad range of plant-rich ingredients.