Attention Deficient Hyperactivity Disorder or ADHD is typically an early onset neurodevelopmental disorder that can persist into adulthood, characterized by symptoms of inattention, impulsivity and hyperactivity. Although the cause of ADHD is still unknown, it's believed to be a complex interaction of genetic and environmental factors including diet and lifestyle. The current approach to treatment is a combination of pharmaceuticals and psychotherapy with some success although pharmaceuticals are often associated with adverse side effects, so many families are looking for alternative treatments. Current research points towards the gut microbiome, immune function, inflammation, and nutrition playing key roles in the development and lasting symptoms of ADHD. Oxidative stress and inflammation markers are higher in ADHD patients as well as mitochondrial dysfunction and alterations in dopamine function. Poor nutrition is considered a major environmental risk factor, so targeted nutrition can improve ADHD symptoms by improving gut health, inflammation and nutrient absorption.
The Microbiome
The gut microbiome is the center health and disease. Many different species of bacteria and other microbes live in the gut and can be influenced by countless environmental factors. Our modern diet of packaged, processed and prepared foods as well as a lifestyle with little to no movement and chronic stress greatly influences gut dysbiosis. Over 40 trillion different microbes protect against pathogens, support the immune system, produce vitamins and short-chain fatty acids (SCFA) in the gut. A diverse and healthy microbial population not only supports absorption and assimilation of macro-nutrients, bile acids and neurotransmitters, it also impacts brain development and mental health.
A strong and relevant connection exist between both gut and brain health, often referred to as the gut-brain axis. The gut microbiota, as the key regulator, directly affecting the central nervous system through the bi-directional gut-brain axis via neurotransmitters, the vagus nerve, hormones, and the immune system. Research shows that people with ADHD have a different composition of gut bacteria that influences how the disorder develops compared to those without symptoms of ADHD people. There is no simple answer as to which bacteria are “good” or “bad” because several factors play a role but, in a recent large study, a high level of Clostridium was significantly associated with ADHD.
The immune system and inflammation
Dysbiosis describes a microbial imbalance where the microbes shift from being protective to pathogenic. The immune system works well if microbes are balanced and the gut is healthy, but if exposed to factors like an unhealthy diet, too much alcohol, antibiotics, stress, other pharmaceuticals or drugs, that system will fail. The barrier function doesn’t work, leading to “leaky gut” which creates systemic inflammation. An over-active immune system, working to manage leaky gut, leads to chronic inflammation. Increased levels of inflammation and dysbiosis have been linked to psychiatric illnesses like schizophrenia, depression, anxiety or ADHD.
Patients with eczema, asthma and allergies have a 30-50% higher chance of developing ADHD. The allergic hypothesis considers that high levels of pro-inflammatory cytokines and immune-associated conditions are associated with ADHD and that inflammation and immunity should be considered in treatment. Ultimately, the way we assess and treat ADHD could change considering the disorder may be a highly inflammatory and immune-associated condition.
Studies show increased levels of inflammatory cytokines IL-1 and IL-6 in patients with ADHD. Food intolerances also increase systemic inflammation by producing the same cytokines. Other adverse food reactions can be immune-mediated as an IgG (sensitivity) or IgA (allergy) antibody response. That means the immune system thinks a particular food is dangerous and attacks it, causing inflammation leading to unpleasant symptoms. If we continue to eat food that is problematic, it will lead to more discomfort, inflammation and ultimately disease. Dietary intervention has been shown to reduce ADHD-like behavior.
Nutrition
A major environmental risk factor for ADHD is diet and because nutrition plays an important role, research has increased over the last few years. Keep in mind a healthy gut microbiome is important for digestion, absorption and assimilation of necessary macro and micronutrients.
The “Western” diet high in saturated fat and simple sugars is a major contributor to gut dysbiosis. By contrast more traditional diets rich in complex carbohydrates in the form of fruit, vegetables, whole grains (fiber), good quality protein and fats are associated with better gut health producing more beneficial microbes. Diets rich in polyphenols (fruits and vegetables) help maintain normal brain function and in particular, polyphenolic extract from pine bark has been shown to reduce hyperactivity and oxidative stress in ADHD. Polyphenols in the diet act as “food as medicine” by modulating the composition of the gut microbiome. Approximately 90% of dietary polyphenols get to the large intestine where they are broken down to helpful metabolites by creating beneficial bacteria while reducing pathogenic microorganisms.
Often, ADHD patients have chronic deficiencies in various nutrients. Some studies show magnesium, iron and zinc, while others show low vitamin D and iodine. Low levels in some of these nutrients can lead to exaggerated symptoms. Omega-3 fatty acids are also commonly low or out of balance with Omega-6 fatty acids. The anti-inflammatory properties of Omega-3s are important and may be beneficial in mental health by regulating brain-derived neurotrophic factor (BDNF). They also regulate neurotransmitter balance and docosahexaenoic acid (DHA) is critical for cognition. Omega-3s produce an antimicrobial effect on the microbiota by increasing bacteria that strengthen the gut lining. It may also create positive impacts by modifying metabolism and consequently the behavioral and cognitive symptoms of ADHD.
Beneficial metabolites are produced by “good” bacteria in a healthy gut. However, short chain fatty acids (SCFA), neurotransmitters and amino acids are less abundant in people with ADHD. SCFA are produced from dietary fiber by microbial fermentation in the gut. They are a major energy source, neuroactive and anti-inflammatory. SCFAs influence the immune system, dopaminergic system and BDNF. Eating foods that contain polysaccharides (fiber) create more SCFA.1 BDNF is important for neuronal survival and growth, it modulates neurotransmitters and supports neural plasticity that is essential for learning and memory. Studies show that plasma BDNF levels in ADHD patients are different that non-ADHD suggesting BDNF may play a role in the disorder. Deficits in dopamine, noradrenalin and/or serotonin play important roles in ADHD. Therefore, the gut microbiota could be a therapeutic target to help with neurotransmitter regulation and transmission.
Supporting good gut health through appropriate nutrition can help improve ADHD symptoms by regulating the immune response, increasing nutrient absorption, and lowering inflammation in the gut and subsequently, the brain.
Studies referenced
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2. Checa-Ros A, Jeréz-Calero A, Molina-Carballo A, Campoy C, Muñoz-Hoyos A. Current Evidence on the Role of the Gut Microbiome in ADHD Pathophysiology and Therapeutic Implications. Nutrients. 2021;13(1):249. doi:10.3390/nu13010249
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