There's no evidence that the behavioral disorder ADHD is caused by diet.
However, research suggests that for some people, dietary changes can improve symptoms.
In fact, a substantial amount of research has examined how nutrition affects ADHD.
This article is an overview of these findings, discussing the foods, diets and supplements involved.
What Is ADHD?
Attention deficit hyperactivity disorder (ADHD) is a behavioral condition involving inattention, hyperactivity and impulsiveness (, ).
It's one of the most common disorders children can have, but also affects many adults (, ).
The exact cause of ADHD is unclear, but research shows that genetics play a major role. Other factors, such as environmental toxicity and poor nutrition during infancy, have also been implicated (, , , ).
ADHD is believed to originate from low levels of dopamine and noradrenaline in the region of the brain responsible for self-regulation (, , ).
When these functions are impaired, people struggle to complete tasks, perceive time, stay focused and curb inappropriate behavior (, , ).
This, in turn, affects the ability to work, do well in school and maintain appropriate relationships, which can decrease quality of life (, , , , ).
ADHD is not considered to be a curable disorder, and treatment instead aims to reduce symptoms. Behavioral therapy and medication are mostly used (, ).
However, dietary changes may also help manage symptoms (, ).
Bottom Line: ADHD is a complicated behavioral disorder, and common treatments include therapy and medication. Dietary changes may also be useful.
Nutrition and Behavior
The science behind food's effects on behavior is still quite new and controversial. However, everyone can agree that certain foods do affect behavior.
Nutritional deficiencies can also affect behavior. One study concluded that taking a supplement of essential fatty acids, vitamins and minerals led to a significant reduction in antisocial behavior, compared to a placebo ().
Vitamin and mineral supplements can also reduce antisocial behavior in children, and poly-unsaturated fatty acids have been shown to decrease violence (, ).
Since foods and supplements have been shown to influence behavior, it seems plausible that they could also affect ADHD symptoms, which are largely behavioral.
For this reason, a good amount of nutrition research has looked into the effects of foods and supplements on ADHD.
Mostly, two types of studies have been performed:
- Supplement studies: Supplementing with one or several nutrients.
- Elimination studies: Eliminating one or several ingredients from the diet.
Bottom Line: Studies show that certain foods and supplements do affect behavior. For these reasons, quite a few studies have looked into how nutrition affects ADHD symptoms, which are mostly behavioral.
Supplement Studies: A Research Review
Many studies have shown that children with ADHD often have unhealthy eating habits or nutrient deficiencies (, , , ).
This caused researchers to speculate that supplements might help improve symptoms.
Nutrition studies have looked into the effects of several supplements on ADHD symptoms, including amino acids, vitamins, minerals and omega-3 fatty acids.
Amino Acid SupplementsEvery cell in your body needs amino acids to function. Among other things, amino acids are used to make neurotransmitters, or signaling molecules in the brain.
In particular, the amino acids phenylalanine, tyrosine and tryptophan are used to make the neurotransmitters dopamine, serotonin and norepinephrine.
People with ADHD have been shown to have problems with these neurotransmitters, as well as low blood and urine levels of these amino acids (, ).
For this reason, a few trials have examined how amino acid supplements affect ADHD symptoms in children.
Tyrosine and supplements have provided mixed results, with some studies showing no effects and others showing modest benefits (, , ).
Bottom Line: Amino acid supplements for ADHD show some promise, but more studies need to be done. For now, the results are mixed.
Vitamin and Mineral SupplementsIron and zinc deficiencies can cause cognitive impairment in all children, whether or not they have ADHD (, , ).
However, lower levels of zinc, magnesium, calcium and phosphorous have repeatedly been reported in children with ADHD (, , ).
Several trials have looked into the effects of zinc supplements, and all of them reported improvements in symptoms (, , ).
Two other trials assessed the effects of iron supplements on children with ADHD. They also found improvements, but again, more research is needed (, ).
The effects of mega-doses of vitamins B6, B5, B3 and C have also been examined, but no improvements to ADHD symptoms were reported (, ).
Nevertheless, a 2014 trial of a multivitamin and mineral supplement did find an effect. The adults taking the supplement showed a convincing improvement on ADHD rating scales after 8 weeks, compared to the placebo group (, ).
Bottom Line: The results from vitamin and mineral supplement studies have been mixed, but several show promise.
Omega-3 Fatty Acid SupplementsOmega-3 fatty acids play important roles in the brain.
Children with ADHD generally have lower levels of omega-3 fatty acids than children who don't have ADHD (, ).
What's more, the lower their omega-3 levels, the more learning and behavioral problems the ADHD children seem to have ().
Therefore, it's not surprising that many studies have found omega-3 supplements to cause modest improvements to ADHD symptoms (, , , , ).
Omega-3 fatty acids appeared to help improve task completion and inattention. Additionally, they decreased aggression, restlessness, impulsiveness and hyperactivity (, , , , , , ).
Bottom Line: Numerous trials have found that omega-3 supplements can bring about modest improvements in ADHD symptoms.
Elimination Studies: A Research Review
People with ADHD are more likely to have adverse reactions to food, causing speculation that eliminating problematic foods might help improve symptoms (, ).
Studies have examined the effects of eliminating many ingredients, including food additives, preservatives, sweeteners and allergenic foods.
Eliminating Salicylates and Food AdditivesBy accident, an allergist named Dr. Feingold discovered that food could affect behavior.
In the 1970s, he prescribed a diet to his patients that eliminated certain ingredients that produced a reaction for them.
The diet was free of salicylates, which are compounds found in many foods, medications and food additives.
While on the diet, some of Feingold's patients noted an improvement in their behavioral problems.
Soon after, Feingold started recruiting children diagnosed with hyperactivity for dietary experiments. He claimed that 30–50% of them improved on the diet ().
His work was celebrated by many parents, who formed the still-existent ().
Although reviews concluded the Feingold diet was not an effective intervention for hyperactivity, it stimulated further research into the effects of food and additive elimination on ADHD (, , ).
Bottom Line: The Feingold diet pioneered elimination diet research for ADHD. It improved symptoms in children with ADHD, although recent evidence is mixed.
Eliminating Artificial Colorants and PreservativesAfter the Feingold diet was no longer considered effective, researchers narrowed their focus to look at artificial food colors (AFCs) and preservatives.
This is because these substances seem to affect the behavior of children, regardless of whether or not they have ADHD (, ).
One study followed 800 children suspected of hyperactivity. 75% of them improved while on an AFC-free diet, but relapsed once given AFCs again ().
Another study found that hyperactivity was increased when 1,873 children consumed AFCs and sodium benzoate, a preservative ().
Even though these studies indicate that AFCs can increase hyperactivity, many people claim the evidence is not strong enough (, , , , , ).
Nonetheless, the FDA requires certain AFCs to be listed on food packages. The EU, on the other hand, requires foods containing AFCs to have a label warning of adverse effects to children's attention and behavior (, , , ).
Bottom Line: AFCs may affect behavior in children, although some say the evidence is not strong enough. However, the FDA and the EU require food labels to list additives.
Eliminating Sugar and Artificial SweetenersSoft drinks have been linked to increased hyperactivity, and low blood sugar is also common in those with ADHD (, ).
Furthermore, some observational studies have found sugar intake to be related to ADHD symptoms in children and adolescents (, ).
However, one review looking into sugar and behavior found no effects. Two trials studying the artificial sweetener aspartame also found no effects (, , ).
Theoretically, it's more likely that sugar causes inattention, rather than hyperactivity, as blood sugar imbalances can cause attention levels to drop.
Bottom Line: Sugar and artificial sweeteners have not been shown to directly affect ADHD. However, they may have indirect effects.
The Few Foods Elimination DietThe Few Foods Elimination Diet is a method that tests how people with ADHD respond to foods. Here's how it works:
- Elimination: Follow a very restricted diet of low-allergen foods that are unlikely to cause adverse effects. If symptoms get better, enter the next phase.
- Reintroduction: Foods suspected of causing adverse effects are reintroduced every 3–7 days. If symptoms return, the food is identified as "sensitizing."
- Treatment: A personal dietary protocol is prescribed. It avoids sensitizing foods as much as possible, in order to minimize symptoms.
The reason why this diet works for some children and not others is unknown.
Bottom Line: The Few Foods Elimination Diet is a diagnostic tool to rule out problems with food. All studies have found a favorable effect in a subgroup of children, usually more than half.
Take Home Message
Research on the effects of food on ADHD symptoms is far from conclusive.
Yet the studies mentioned here suggest that diet can have powerful effects on behavior.