Although medicine classifies ADHD (attention-deficit/hyperactivity disorder) as a brain disorder, parents and academics have speculated for decades that certain foods may have something to do with the typical symptoms of inattention, restlessness and overactivity.
Now, the evidence is too compelling to ignore: study after study shows that certain foods-or agents within foods-may contribute to ADHD-related behaviours and that removing them from the diet might actually improve, or even reverse, these behaviours.
We've identified five likely suspects lurking in your kids' foods that could be making them hyperactive, based on the latest research, and what to avoid for a calmer child.
Artificial colours and preservatives
Synthetic food additives have long been suspected of causing or worsening hyperactive behaviour in children, and a well-designed study published in The Lancet in 2007 confirmed the link. The six-week trial involved giving healthy three-year-old and eight/nine-year-old children drinks containing additives-artificial colours and the preservative sodium benzoate-or a placebo drink, and monitoring their behaviour via parents, teachers and computer tests. The researchers discovered a significant increase in hyperactivity in both age groups of children during the weeks they consumed the additive-containing drinks.1
Other investigators-who pooled the results of 34 separate studies-estimate that 8 per cent of children with ADHD may have symptoms related to synthetic food colourings.2
What to avoid: Sweets, colourful cereals, fizzy drinks, cake mixes. Forgo processed and packaged foods as much as possible in favour of fresh, whole foods; if you do buy packaged items, look for those that are free of artificial additives.
This ubiquitous plastics chemical is commonly found in canned food; it can leach from the linings of cans into the product inside. One US study tested 12 canned-food items marketed to children, including Campbell's Disney Princess and Toy Story soups, and found detectable amounts of bisphenol A (BPA) in every single sample tested.3
Although the UK's Food Standards Agency insists that the levels of BPA found in food are not a health concern, evidence suggests that even low doses can have a detrimental effect on childhood behaviour. A recent study found that children with higher concentrations of BPA in their urine at age five were more likely to display inattention and hyperactivity behaviours at age seven-even though their BPA levels were generally lower than the US average.4 Other research shows that exposure to BPA in the womb-at levels commonly found in the general population-could contribute to aggressive and hyperactive behaviour in early life.5
What to avoid: Canned and plastic-wrapped food, plastic water bottles, plastic food containers with a number 7 recycling code. Choose fresh, unprocessed foods whenever possible.
Organophosphate pesticides, which turn up in our food and drinking water, have been linked to a host of serious health problems and may be particularly toxic to developing brains.
In a representative sample of US children, those with higher levels of organophosphate pesticide breakdown products in their urine were more likely to have ADHD than children with lower levels.6
Previous studies found associations between pesticide exposure and attention/behavioural problems, but this was the first to link the low levels of pesticide exposure seen in the general population to adverse health effects. "Each 10-fold increase in urinary concentration of organophosphate metabolites was associated with a 55 per cent to 72 per cent increase in the odds of ADHD," said lead study author Maryse Bouchard, PhD, working at Harvard's Department of Environmental Health at the time.
What to avoid: Non-organic produce, especially fruit and vegetables. If you can't afford to go completely organic, check consumer watchdog Environmental Working Group's Guide to Pesticides in Produce (www.ewg.org/foodnews) to work out which foods have the most and least pesticide residues.
Another environmental pollutant that's finding its way into food, mercury has also been associated with behavioural problems and ADHD.
A Boston University School of Public Health study published in 2012 discovered that children born to women with higher levels of mercury during pregnancy were more likely to exhibit signs of ADHD at age eight. On the flipside though, the researchers also found that the children whose mothers ate the most fish while pregnant-one of the main sources of mercury in the diet-were the least likely to show inattentive and hyperactive behaviours.7
Fish is rich in omega-3 fatty acids-crucial for brain development and function-and a lack of them could be involved in ADHD.8 But as fish can also contain mercury, which is toxic to the brain, the trick is to eat only those types of fish low in mercury. Good choices for women and children that offer the greatest health benefits and lowest mercury levels include salmon (wild), herring, mussels, sardines, anchovies and trout, according to The Environmental Working Group.9
But mercury may also be hiding in processed foods and drinks containing the sweetener high-fructose corn syrup (HFCS); the contaminant can sneak in as a result of some manufacturing processes.10 Some researchers have even speculated that the introduction of HFCS into the food supply could be a contributory factor to the recent alarming rise in cases of ADHD and other developmental disorders like autism.11
What to avoid: Anything with HFCS or glucose corn syrup on the label, plus fish high in mercury like seabass, shark and swordfish, and even species moderately high in the contaminant, including haddock, hake and canned tuna. Go for low-mercury fish varieties or choose a high-quality fish-oil supplement to avoid other contaminants too.
Even healthy foods have the potential to cause hyperactivity and behavioural problems in children if they're sensitive to them. Dr Lidy Pelsser, of the ADHD Research Centre in the Netherlands, estimates
that around two-thirds of ADHD cases are the result of hypersensitivity to foods.
She tested the theory on 100 children with ADHD, aged between four and eight years, who were randomly assigned to five weeks of either a restricted elimination diet or a general healthy diet (as a control). By the end of the trial, 64 per cent of the children on the restricted diet reported a dramatic decrease in, or a complete reversal of, ADHD symptoms, while none of those on the general control diet reported any such improvement.12
What to avoid: Wheat, dairy, eggs, chocolate and oranges are key suspects. If eliminating them from your child's diet doesn't make much difference, try avoiding salicylates, found in apples, berries, courgettes, peppers and a variety of other foods. Many parents swear by the Feingold diet, which eliminates salicylates as well artificial colourings, flavourings and certain preservatives, and has proved useful for ADHD in some studies.13 Consider consulting a nutritional therapist experienced in allergy treatment to find the right diet for your child.
1 Lancet, 2007; 370: 1560-7
2 J Am Acad Child Adolesc Psychiatry, 2012; 51: 86-97.e8
4 Environ Res, 2013; 126: 43-50
5 Environ Health Perspect, 2009; 117: 1945-52
6 Pediatrics, 2010; 125: e1270-7
7 Arch Pediatr Adolesc Med, 2012; 166: 1123-31
8 Int Rev Psychiatry, 2006; 18: 155-72
10 Behav Brain Funct, 2009; 5: 44
11 Clin Epigenetics, 2012; 4: 6
12 Lancet, 2011; 377: 494-503
13 Aust Paediatr J, 1988; 24: 143-7