The value in identifying causes, is that these can often give us clues as to what might be helpful in treating that ailment or disorder. For example, if it were found that people who have ADD tended to be low in a certain protein, that could be boosted or supplemented in the diet, and improvements would likely follow.
As with most cognitive or neurological issues no single factor has been identified as the definitive cause of ADD or ADHD; instead, they are more likely due to several variables including the following:
Genetics
A considerable portion if not most ADHD cases are thought to be attributable to genetics, i.e. inherited. Dr. Amen has noted that in his clinical practice as well. A number of specific genetic variations are associated with ADHD. These are predominantly related to the regulation of dopamine (a chemical messenger used by brain cells). The importance of dopamine in ADHD is highlighted by the fact that methylphenidate (Ritalin), is thought to treat ADHD symptoms in part by increasing dopamine signaling in the brain.(*)
Fortunately, due to more recent studies in the field of epigenetics (over/above genetics) we now know, that the expression of genes can be determined by a variety of other factors, which can turn them off or on, factors such as those below.
Environmental Factors
Environmental toxins such as polychlorinated biphenyls (PCBs), some pesticides, and lead have been linked to ADHD development, but no studies have proven that they directly cause the disorder. Other external factors, such as harsh or negative child-parent interactions and poor or a lack of early social contact, have been found to contribute to ADHD onset.(*)
Also some variables in utero (in the womb), including maternal smoking during pregnancy, premature birth and/or low birth weight, and/or maternal stress, are seen as risk factors but not causative links to ADHD.(*) https://pubmed.ncbi.nlm.nih.gov/22963644/
Some recent fMRI brain imagine has shown that the brain networks in children with ADHD may activate in different patterns compared with healthy children’s brains. Other studies suggest brains of children with ADHD display variations in volume or density of various brain regions compared with non-ADHD kids.
These findings correlated with SPECT scans of children with ADHD conducted Dr. Amen’s team
Traumatic brain injury (TBI) has also been linked to behaviors similar to those observed in ADHD. Approximately 20–50% of children who suffer a TBI develop a form of clinically relevant attention disorder termed secondary ADHD. It is uncertain if mild TBI, which is commonly experienced by children, increases the risk of ADHD-type behaviors developing.(*)
In a 2003 study, scientists listed eight general categories of possible contributors to ADHD (7 of which had to do with diet, or nutrition): food and additive allergies, environmental toxicity (see above), dietary deficiencies in proteins or excesses in simple sugars, mineral imbalances, deficiencies in cell membrane components (essential fatty acids and phospholipids), deficiencies in certain amino acids, thyroid disorders, and deficiencies in B vitamins. https://www.lifeextension.com/magazine/2006/11/atd
Several of these factors noted above are likely related. For example low dopamine levels usually reflect low levels of the amino acid (protein) L-Tyrosine (the primary precursor for dopamine), and low tyrosine, has also been linked to low thyroid issues, and low vitamin B-6, as well as attention issues.
Moreover, we know that one of the reasons why stimulant drugs such as Ritalin® or Adderall® are helpful for many with ADHD is due to the fact that they promote the release of dopamine in brain tissue. However, dopamine levels and signaling are naturally increased with the consumption of the L-tyrosine. See the following link for more info on this important amino acid. https://www.verywellmind.com/can-l-tyrosine-help-with-adhd-symptoms-5248442
Additionally, studies have found evidence for insufficiency or imbalance of omega-3 and omega-6 fatty acids in people with ADHD. (Typically they have too much omega-6 from highly processed foods and oils from soybeans, corn, cottonseed and canola oil, and not enough Omega-3 from healthy fish, flax, hemp and other healthy seeds.)(*)
Zinc and magnesium intake have been found to be reduced in those with ADHD, while iron and vitamin D deficiency also may increase risk of ADHD. Iodine is particularly important for thyroid function and the developing brain, and has been shown to often be deficient in children with ADHD.(*)
On the foods to avoid side, excessive sugar intake has often been linked to ADHD by parents, although the majority of research has largely debunked this as unsubstantiated; definitive evidence for a causal relationship is currently lacking. Higher intake of sugar, candy, and soft drinks has been shown to be associated with a higher prevalence of ADHD in children and adolescents with a new ADHD diagnosis.(*)
Additionally, limited evidence suggests high intake of certain food additives, such as artificial colorings, may contribute to hyperactivity in those with ADHD as well.(*)
