Contributing factors are substances, contexts or conditions that have roles in the causation or promotion of attention deficit hyperactivity disorder.

Diet and Mental Health 

Diet is commonly considered the most important mediator of health and disease.

Patients with psychiatric disorders often have poor food patterns, either from a reduced appetite, skipping meals, consuming fast or processed foods, or a general lack of interest in food altogether. (Greenblatt & Brogan, 2016).

Diet and ADHD

ADHD is associated with a “Western-style” diet, which is high in refined sugars and fats (Millichap & Yee, 2012).

Nutritional imbalances from poor diet in early childhood can cause behavioral issues in late childhood (Wiles 2009).

• • Consuming lots of junk food (high-fat, processed foods, burgers, fried chicken, snack foods high in fat and/or sugar, chips, chocolate) at age 4 was later connected to increased hyperactivity (age 7) (Wiles 2009).

Sugar-restricted, additive-free, and preservative-free diets that are supplemented with Omega-3s can reduce ADHD symptoms (Millichap & Yee, 2012). See the Mediterranean diet below:

Mediterranean diet and anxiety

• The Mediterranean diet is considered a good model for a healthy diet. It includes foods that are beneficial and reduces or elimates foods that promote mental health issues.
• General components of the Mediterranean diet include:
  • plenty of vegetables and fruit
  • healthy fats including olive oil
  • regular consumption of seafood
  • poultry, beans, and small amounts of red meat
  • small amounts of dairy such as yogurt and cheeses.
  • whole grains instead of refined grains

Elimination Diets and ADHD

Comprehensive elimination diets:

• Typical elimination diets for ADHD simultaneously exclude refined sugar, food additives, common food allergens, salicylates, and amines. This can be a difficult diet to follow.
• Substantial improvement can be achieved in many cases [of ADHD] after eliminating just the refined sugar, food additives, and common food allergens (Gaby, 2011).

Oligoantigenic diets (restricted elimination diet, hypoallergenic diet):

• Eliminate highly allergenic foods such as cow’s milk, cheese, egg, chocolate, and nuts. Oligoantigenic diets can vary in their strictness (Ly et al., 2017).

The oligoantigenic diet often involves an elimination phase (usually two to five weeks). During this phase, all of the food items are completely removed. (Ly et al 2017). The elimination phase could consist of only a few hypoallergenic foods such as rice, turkey, lettuce, pears, and water (Ly et al., 2017).

The oligoantigenic diet promotes the reduction of ADHD symptoms (Ly et al., 2017). After the elimination period, foods are reintroduced slowly to identify ‘problem’ foods. Re-introduction of problematic foods often causes reappearance of ADHD symptoms (Ly et al 2017)

Fiengold Diet and ADHD

The Feingold Diet is a type of elimination diet that eliminates certain food chemicals and  salicylates. The Feingold Diet has been shown to be effective in addressing ADHD symptoms. See more in the Food Additives section.

Additional information

Mediterranean diet for heart health
Mayo clinic

https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/mediterranean-diet/art-20047801

Sugar and Mental Health

Refined sugars are sources of carbohydrates, but lack the nutrients required for their metabolism (breakdown in the body). As a result, the body’s reserves of nutrients are used instead. With chronic sugar consumption, the body becomes depleted in nutrients – especially those that are important for mental health.

Elevated consumption of sugar can promote:

• damage to neurons by promoting oxidative stress and inflammation in the brain (Meng et al., 2014)
• cognitive impairments and neurodegenerative disorders (Jacques et al., 2019)
• insulin resistance, which in turn, can promote neurodegenerative disorders (Cetinkalp et al., 2014)

Sugar and ADHD

Refined sugar is one of the most common foods that induces ADHD symptoms in children (Gaby, 2011).

• “Glucose and insulin metabolism issues can promote neuropsychiatric symptoms through several different mechanisms” (Gaby, 2011)

The relationship between ADHD and refined sugar has been shown through clinical observation and research (Gaby, 2011)

• A strong positive association between soft drink consumption and odds of mental health issues was found, particularly in teens consuming 4+ soft drinks/day. Levels of hyperactivity directly connected to the number of soft drinks consumed (Lien et al 2006)

Gluten and ADHD

Gluten is a general name for proteins found in wheat and related grains. Although many people are not affected by gluten, for a variety of reasons for others it can cause problems..

• Gluten can damage the digestive tract, resulting in decreased nutrient absorption, and increased inflammation
• The gliadin component of gluten can be improperly converted into gluteomorphins – which are addictive. Withdrawal symptoms include anxiety, depression (Scott, 2011)
• Gluten sensitivity can decrease serotonin (Pynnönen 2005). Low serotonin is a risk factor for several mental health conditions.

Celiac disease and gluten

• Celiac disease is an autoimmune condition triggered by consumption of gluten.  Not all symptoms of celiac disease manifest in the digestive system (Naidoo, 2020; Anderson, n.d.; Jackson et al., 2011).
• The neurological and psychiatric symptoms associated with celiac disease may mimic those of ADHD.  (Medicine.net, 2017; Ertürk et al., 2020). Ruling out celiac
  disease may be helpful to the formal diagnosis of ADHD (Medicine.net, 2017).
• Studies have found that symptoms indicative of ADHD are more prevalent in individuals with celiac disease than in the general population (Niederhofer & Pittschieler, 2006; Anderson, n.d.; Jackson et al., 2011).  These symptoms may improve with strict adherence to a gluten-free approach to eating (Niederhofer & Pittschieler, 2006; Anderson, n.d.; Jackson et al., 2011; Ertürk et al., 2020; Medicine.net, 2017).

Non-celiac gluten sensitivity and ADHD

• Individuals with a non-celiac sensitivity to gluten may also experience psychiatric and neurologic symptoms associated with ADHD (Jackson et al., 2011).
• Consumption of foods containing gluten may worsen symptoms experienced by individuals with ADHD, especially if they have a non-celiac gluten sensitivity (Naidoo, 2020; Anderson, n.d.).
• Absorption of nutrients supportive of balanced brain chemistry may also improve with removal of gluten from the diet (Gore, n.d.).

Some sources of gluten (Sources of Gluten, n.d.)
• wheat, rye, barley, triticale, malt, brewer’s yeast, wheat starch, pastas, noodles, bread, crackers, baked goods, cereals, sauces and gravy, beer

Food Additives

Food additives are substances that get added to food to improve safety, taste, appearance, etc. Food additives can cause ADHD symptoms either through pharmacological effects or because of non-allergic (pseudoallergic) reactions (Gaby, 2011). Pseudoallergic reactions are generally not revealed by typical allergy tests (IgE, IgG RAST) (Gaby, 2011).

Artificial colours and sodium benzoate preservatives (in combination or separately) increase hyperactivity in children (McCann 2007).

• “An estimated 8% of children with ADHD may have symptoms related to synthetic food colors.” (Nigg 2012)
• When artificial colours and flavours, chocolate, MSG, preservatives, and caffeine were removed from the diet for 10 weeks, more than half of the children showed improvement in behavior, and reduced sleep problems (Kaplan 1989).

Salicylates and ADHD

Salicylates are natural substances found in some fruits and vegetables as well as aspirin and other pain medication. It has been reported that 30–50% of children with ADHD showed marked improvement in ADHD symptoms after avoiding salicylates with results usually apparent within 3 to 21 days (Gaby, 2011).

Feingold Diet and ADHD

The Feingold Diet is a form of elimination diet that removes certain harmful food additives as well as the aspirin-like chemical salicylate. Salicylates have been found to promote symptoms of ADHD (Ly et al., 2017). The benefits of the Feingold Diet approach have been confirmed by clinical observations, uncontrolled and double-blind trials (Gaby, 2011).

Chemicals removed in the Feingold diet (FAQ | Feingold Association, n.d.):

• artificial (synthetic) food dyes
• artificial (synthetic) flavorings & fragrances
• artificial sweeteners
• three specific food preservatives

Also removed from the diet:

• Foods and non-foods containing salicylates
• Aspirin and medicine containing aspirin

Lead and Mental Health

Toxic levels of lead are associated with (Pataracchia, 2008):

• psychosis
• behavioural issues
• mood disorders
• learning disabilities
• insomnia
• compromised immunity
• brain damage
• delayed infant development
• disruption of thyroid hormone transport

Lead is involved in several processes, including:

• Blocking N-methyl- D-aspartate (NMDA) glutamate receptors, which affects brain plasticity and organization.
• Replacing calcium and altering cellular function (Brochin et al 2008)
• Free radical production
• Neurotransmitter generation (Verlaet et al., 2018)
• Midbrain dopamine circuitry

Low-level lead exposure remains a potential influence on ADHD, due to its abundance internationally, and it’s role in disrupting midbrain dopamine circuitry, as it is the same circuitry involved in ADHD (Nigg et al., 2008)

Lead and ADHD

Children with ADHD or learning disabilities have significantly higher levels of lead than healthy children. (Gaby, 2011). These higher levels are associated with increased hyperactivity symptoms and higher ratings of attention-deficit behaviour.

The current population average of lead blood levels in children in the US  is 1–2 μg/dL (Nigg et al., 2008). Blood lead levels of up to 10 μg/dL are associated with:

• lower child intelligence scores
• weaker executive cognitive abilities
• behavioural symptoms of ADHD (inattentiveness, hyperactivity
• diagnosis of ADHD

Lead & ADHD symptoms

• Children with high lead levels had almost 3x the odds of inattentive and hyperactive symptoms. Children with low lead levels showed risk of ADHD symptoms (Kim 2010)

Removing lead improves symptoms. When treated with a chelating agent (EDTA or penicillamine) to reduce high lead levels, ADHD patients showed clinical improvement, which sometimes was after an initial worsening of behaviour (Gaby, 2011).

Sources of Lead Exposure

Lead exposure via water, soil, and other sources remains a worldwide health concern (Nigg et al., 2008).

Common sources of lead exposure (Common Sources of Lead, n.d., Campbell, 1995):

• lead-based paint
• children’s toys and jewelry
• mini blinds
• imported candy
• lead water pipes
• drinking water
• newsprint
• organ meats
• tobacco
• cosmetics
• workplace and hobby hazards
• traditional home remedies and cosmetics
• lead-glazed ceramic ware, pottery and leaded crystal
• contaminated soil
• car batteries
• leaded gas (which may persist in the environment still) (Eschner, 2016)

Addressing Lead Toxicity

Environmental and dietary sources of toxic metal exposures need to be removed as much as possible.

Many patients will improve with a basic protocol of a healthy diet, supplementation of essential nutrients, exercise, and rest. Sweating from exercise or sauna can also help remove toxic metals (Sears, 2018).

Detoxification of toxic metals must be properly supported with a protocol tailored to the patient’s unique situation and toxic load, in order to minimize the risk of releasing, then depositing the metals back into tissues. The best approach for brain detoxification is conservatively, “with repeated, modest treatments, using multiple agents” (Sears, 2018).

Food allergies and sensitivities

Food allergies and sensitivities that affect the brain can be referred to as “cerebral allergies”. Cerebral allergies include more than just antibody-antigen reactions.

Cerebral allergies are mediated by:

1. Direct biochemical effects of substances found in food or drink, for example caffeine, alcohol, and sugar
2. Hidden or delayed allergic reactions to food or drink, for example wheat, milk, corn, and egg

Foods commonly associated with allergies (Prousky, 2015):

• dairy products
• wheat, rye, barley
• eggs
• pork, beef, seafood
• soy
• corn, tomato
• citrus fruits
• nuts, peanuts
• chocolate
• coffee, tea
• sugar
• yeast

Food Allergies and ADHD

Studies have shown that children with ADHD have a higher risk of developing allergies and that food allergies are a common cause of ADHD (Ly et al., 2017). “Children with ADHD are 7x more likely to have food allergies” (Bellanti 2001; Greenblatt, 2018).

Adverse food reactions associated with ADHD are often surrounding wheat and dairy. Both dairy and wheat show reaction types including (Greenblatt, 2018):

• IgG Food Allergy
• IgE Food Allergy
• Suboptimal DPP IV
• Autoimmune

​​IgG food allergy symptoms include (Rapp 1991):

• hyperactive, uncontrollably wild, unrestrained
• nonstop talk, repetition, loud talk, stuttering
• inattentive, disruptive, impulsive
• short attention span and inability to concentrate
• nervous, irritable, upset, short-tempered, moody
• high-strung, excitable, agitated

Eliminating Food Allergies 

The most frequent symptom-evoking foods have been found to be (starting with most common):

• sugar
• colours (especially red), additives, and flavours
• milk/dairy
• corn
• chocolate
• egg
• wheat
• oats
• soy
• citrus
• pork

Less frequent symptom-evoking foods were beef, apple, chicken, grape, peanut, onion, pineapple, tomato, carrot, oats, rice, and lettuce (Gaby, 2011).

The Microbiome

• The human microbiome is made up of 10-100 trillion microbial cells consisting of bacteria, fungi, and viruses, among many others.
• The microbiome also includes the genes contained by these cells (Ursell et al., 2012).
• The composition of the microbiome is influenced by changes in diet and health (Quigley, 2013).

The microbiome is affected by:

• antibiotics
• infections
• dietary sucrose (sugar and starch consumption)
• dietary chemicals – including pesticides, additives and preservatives
• medications – NSAIDs, Prednisone, oral contraceptives
• food intolerances
• location of birth
• the birthing process
• formula feeding

The Gut-Brain Axis and Mental Health

• The gut-brain axis includes the brain, spinal cord, autonomic nervous system (sympathetic, parasympathetic and enteric nervous systems), and the hypothalamic-pituitary–adrenal (HPA) axis (Dinan et al., 2015).
• Mental health conditions affected by the gut-brain axis include anxiety, depression, autism, obsessive compulsive disorder, and schizophrenia.

The Microbiome and ADHD

• Evidence has shown that the microbiome plays a large role in the development and progression of many psychiatric and behavioural disorders such as Attention Deficit/Hyperactivity Disorder (ADHD). (Understanding Gut Microbial Link with ADHD – an Update, n.d.)
• The gut microbiome of ADHD individuals is different than the average healthy individual. It has been suggested that gut microbial imbalance can alter the gut and brain barriers, which leads to chronic inflammation and neurotransmitter dysfunction, which then can contribute to the development of ADHD. (Understanding Gut Microbial Link with ADHD – an Update, n.d.)

Probiotics and ADHD

• Children with ADHD have been found to have significantly fewer probiotic species at early age (Pärtty, 2015).
• Mothers taking Probiotic Lactobacillus rhamnosus GG for 4 weeks before delivery and for 6 months after delivery resulted in:
  • No children treated with the probiotic were diagnosed with ADHD or ASD, compared to 17% of untreated children (Greenblatt 2018).
  • Supplementation with Lactobacillus acidophilus and bifidus showed similar effects on ADHD symptoms (attention, self control) as 5-15 mg Ritalin 2-3 times daily for four weeks (Harding 2003; Greenblatt 2018).

Oxidative Stress

Oxidative Stress is a biological condition that results in excess accumulation of oxidants as a result of (Moghadas et al, 2019):

• production of excessive amounts of oxidants
• decreased level of antioxidants
• a combination of both events

People are constantly exposed to free radicals, which are unstable atoms that can damage other cells. Exposure to free radicals in the environment can be from (Moghadas et al, 2019):

•  Electromagnetic radiation from the man-made environment (pollutants, cigarette smoke)
• Natural resources (radon, cosmic radiation, cellular metabolisms)

Oxidative Stress and ADHD

• Excessive amounts of free-radicals and/or an ineffective anti-oxidant system can cause changes in proteins, and damage to membranes and DNA structure. Therefore, there is some evidence suggesting a correlation between ADHD and oxidative stress levels (Moghadas et al, 2019).
• It has been suggested that oxidants can inhibit the uptake of enzymes and/or neurotransmitters. Since these are a part of the physiological functioning of cells, they could be seen as a predisposing factor for ADHD (Moghadas et al, 2019).
• Changes in oxidative metabolism have been reported as a major factor in the cause of ADHD (Moghadas et al, 2019).

ADHD Patients have been found to have (Ceylan et al 2010):

• significantly higher markers of reactive oxygen molecules (known as reactive oxygen species) and lipid peroxidation (nitric oxide and MDA)
• inhibited antioxidant activity (such as low glutathione peroxidase activity)
• oxidative damage to neurons