Attention deficit-hyperactivity disorder (ADHD), is a neurological condition associated with the brain’s chemistry and anatomy, is one of the most common neurobehavioral disorders of childhood. It can persist through adolescence and into adulthood. A conservative estimate is that it affects 3–7% of school-age children, and may occur in 4.4% of the adult population. Although questioned in the past whether ADHD is a real disorder, new evidence shows that ADHD is a heritable disease with a genetically determined basis.
WHAT ARE THE SYMPTOMS OF ADHD?
ADHD symptoms may include social withdrawal, shyness and anxiety, and in some children, impulsivity, difficulty controlling behavior and inattention. Children with ADHD often have learning difficulties, such as problems with reading and writing. There are three recognized types of ADHD: predominantly inattentive, hyperactive-impulsive and combined inattentive hyperactive-impulsive type, the most common form. Hyperactive children are constantly in motion, impulsive children are unable to curb their reactions or think before they act, and inattentive children have a hard time keeping their minds on any one thing and may get bored with a task after only a few minutes. These types of ADHD are recognized by the following traits:
ADHD children with inattention often:
- Are easily distracted
- Appear not to listen when spoken to
- Have difficulty following directions or finishing tasks
- Have difficulty staying organized
- Misplace things
Hyperactive children with ADHD typically have these characteristics:
- Difficulty remaining seated and waiting for their turn
- Fidgeting and bouncing while seated
- Talking too much
- Seeming to be in constant motion
- Climbing on and jumping off things inappropriately
- Running inappropriately
Impulsive ADHD children often:
- Have great difficulty waiting for turns
- Interrupt children’s play activities and conversations
- Blurt out answers to questions not directed at them
- Act recklessly without thinking of the consequences
Adults with ADHD may have difficulty following directions, remembering information, concentrating, organizing tasks or completing work within time limits, and these difficulties can cause behavioral, emotional, social, vocational and academic problems. No two people with ADHD have the same cluster of symptoms.
WHAT CAUSES ADHD?
Currently, the causes of ADHD are unknown with certainty, but they involve both genetic and environmental factors that differ among individuals. Over 25 years ago, researchers observed signs of fatty acid deficiency in hyperactive children. It is also known that severe deficiencies in essential fatty acids, including long-chain omega-3s, can cause profound mental retardation. Deficiencies in long-chain omega-3 fatty acids are known to affect behavior and cognition both directly and indirectly. Evidence to suggest a link with ADHD derives in part from human studies that reported reduced plasma omega-3 fatty acids in ADHD subjects. Studies have shown that abnormally low intakes or tissue levels of various types of polyunsaturated fatty acids (PUFAs), including omega-6s and omega-3s, are associated with ADHD. For example, some studies reported that ADHD children and adults had less long-chain omega-3s in their tissues than individuals without ADHD. Such reductions in docosahexaenoic acid (DHA), a long-chain omega-3 PUFA, and in total omega-3s and arachidonic acid, a long-chain omega-6 PUFA, may persist into adulthood. Although earlier research suggested that low status of omega-3s was associated with elevated behavioral and possibly cognitive symptoms of ADHD, recent research revealed few associations between PUFAs and cognition in adults with ADHD. Other studies in children with ADHD showed that their plasma fatty acids did not reflect an omega-3 PUFA deficiency.
Nutrition can influence the expression of genes related to enzyme production, potentially predisposing children to nutrient deficiencies. It is plausible that some of the numerous genes already known to influence fatty acid metabolism may contribute to the risk for inter-related developmental and psychiatric disorders. Several genes have been associated with ADHD, including one affecting PUFA metabolism, one affecting the dopamine transporter gene and another affecting the production of neurosteroids, substances that alter neuronal activity. However, it is not clear how dietary variables might affect the expression of these genes in ADHD. Other evidence that relates to PUFA metabolism suggests that some ADHD individuals have higher rates of oxidative breakdown of omega-3s. This might explain why omega-3s are lower in some individuals. Further, oxidation products might damage nerve tissue. Observations like these have led to the hypothesis that insufficient amounts of specific fatty acids affect brain function in such a way as to cause or worsen the symptoms of ADHD.
WHY ARE OMEGA-3s SO IMPORTANT IN BRAIN FUNCTION?
There are the two “families” of essential fatty acids, omega-3 and omega-6. Omega-3s, being required for both structure and function, are needed for children’s brains to develop properly. These fatty acids cannot be synthesized from scratch in the body, and must be obtained from the diet. PUFAs make up about 20% of the brain, and in the nervous system as a whole, one out of every three fatty acids is polyunsaturated. PUFAs are critical structural components of cell membranes and nerve tissue, and omega-3s, particularly DHA, are essential for the formation of new tissue, thus they are important for development and growth. The potential biological mechanisms that explain the impact of omega-3s on neurological disorders are complex and are still being investigated for verification.
LONG-CHAIN PUFAs AS A TREATMENT FOR ADHD
So, what is the scientific evidence that PUFAs may be effective in lessening the symptoms of ADHD? The studies of relationships of PUFAs to ADHD to date have had limitations that often make it difficult to compare the results of one study with others. These limitations are in part responsible for conflicting study outcomes. Among these limitations are mixed diagnosis of participants; differences in doses, products and duration; small numbers of participants; combined treatment with special diets and medications; concurrence or other health conditions; different treatment durations; variable statistical methods; etc. In spite of the many limitations, the evidence summarized below suggests that the symptoms of ADHD may be related to long-chain PUFAs, including omega-3 PUFAs.
The observations that hyperactive children have signs of fatty acid deficiency, and that ADHD and other neurodevelopmental disorders may be associated with inadequate levels of essential fatty acids, suggest that ADHD symptoms might be addressed with a nutritional or dietary approach involving omega-3-rich fats. Clinicians investigating a link between diet and hyperactivity found that flax oil, high in the omega-3 alpha-linolenic acid (ALA), decreased ADHD symptoms in children and improved attention in healthy adults. Although our bodies have the enzymes necessary to make the more biologically active long-chain omega-3s from ALA, very little is converted to eicosapentaenoic acid (EPA) and almost none goes to DHA. Thus, these two omega-3s appear to come primarily from the diet or body stores and not from ALA metabolism.
Long-chain omega-3s have been helpful to ADHD patients in some but not all studies. Symptoms of ADHD in children treated with omega-3s were significantly improved compared with non-ADHD children in two large studies, one in the United Kingdom and a second in Australia. Children with a primary diagnosis of dyslexia and secondary ADHD-type symptoms received an omega-3/omega-6 combination or olive oil for 3 months. Those consuming the omega-3/omega-6 combination experienced significantly greater benefits than children in the olive oil group with respect to inattention, anxiety/withdrawal and disruptive behavior.
Further evidence of long-chain omega-3 effectiveness in treating ADHD children was reported by a psychiatrist who described significant improvements in behavior (inattention, hyperactivity, oppositional/defiant behavior and conduct disorder) in children supplemented with a high amount of EPA/DHA concentrates each day for 8 weeks.
When children with primarily ADHD-type difficulties were treated for 4 months with an omega-3/omega-6 formula from fish oil plus evening primrose oil (high in gamma-linolenic acid, an omega-6 fatty acid), there were significant benefits for attention and behavior and on clinical ratings of oppositional defiant disorder. In a similar study, ADHD children given capsules containing 2,400 mg fish oil and 600 mg evening primrose oil daily for 15 weeks had significant improvements in many areas relating to hyperactivity and inattention compared with ADHD children given placebo. An additional 12-month long study is currently comparing the benefits of EPA- and DHA-rich oils on ADHD symptoms and literacy in children with ADHD and learning difficulties.
In yet another recent study, a majority of ADHD children and adolescents treated for 3 months with omega-3/omega-6 did not respond; however, a subgroup of participants characterized by inattention and associated neurodevelopmental disorders responded with more than a 25% reduction of symptoms, and after 6 months, 47% of all children showed such improvement.
In a larger number of children with a related neurological condition—developmental coordination disorder—treated with long-chain omega-3 and omega-6 PUFAs, symptoms improved significantly, but again, to a very small extent. Although some studies to date show that children treated with omega-3 supplements did not outperform those taking a placebo, other reports suggest that these supplements may have had a modest effect on attention and hyperactivity symptoms in children with developmental coordination disorder.
In spite of the promising results of some studies, others show no significant effect of treating ADHD children with omega-3s. For example, children undergoing maintenance therapy with stimulant medication were given 345 mg DHA per day for 4 months. Although their blood DHA levels went up, the 4-month treatment did not decrease symptoms of ADHD. However, a small number of children not diagnosed with ADHD, but with ADHD-related symptoms and treated with omega-3s, exhibited a modest beneficial effect. Unfortunately, studies with small numbers of children with different time intervals for treatment and different forms of omega-3s do not permit conclusions about the long-term effectiveness of omega-3 treatment on ADHD. Certainly further studies with a mixture of high-dose omega-3/omega-6 fatty acids for longer time intervals are worth investigation.
No nutrient works in isolation, and essential micronutrients like zinc also provide benefits for ADHD. Zinc is an essential co-factor in the synthesis of PUFAs; hence, these findings seem to be relevant to a basis for its benefits for ADHD. It is unlikely that a single cause will be found for ADHD. Nutrient deficiencies are common in ADHD, and supplementation with minerals, the B vitamins, omega-3 and omega-6 fatty acids, and flavonoids have potential to decrease ADHD symptoms. Multiple forms of treatments are probably needed to treat patients with ADHD, and may include nutritional, environmental, pharmacologic and psychosocial interventions.
What conclusions can individuals derive from currently available information on long-chain omega-3s and ADHD? At this time, we do not know with certainty whether fatty acid abnormalities associated with ADHD are the result of differences in diet, genetic factors or fatty acid metabolism. So far, we know that children with ADHD who have low amounts of omega-3 EPA and DHA in their bodies have more learning and behavioral problems than those with normal amounts. As yet, we do not know the optimal amount of omega-3s and omega-6s given separately or together that are most effective in different types of ADHD. However, preliminary evidence from treatment trials suggests that long-chain omega-3s may be a useful adjunctive treatment for ADHD and related childhood developmental conditions. Overall, with better study designs for future studies, more attention to dose and treatments, and greater selectivity of participants, consistent directions in outcomes are beginning to emerge. Although it is not yet possible to recommend omega-3s for primary treatment of any mental or behavioral disorder, there is sufficient evidence to justify continued clinical study to further examine the ability of long-chain omega-3 supplements to improve the symptoms of ADHD. Ensuring that the diet provides a regular source of long-chain omega-3s through eating fish twice a week as recommended by the American Heart Association, or consuming fish oil supplements or omega-3-enriched eggs is a reasonable approach for someone with ADHD.
*A fully referenced version of this article is available from the editor.