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Diet and ADHD: Separating myth from clinical reality
As schools return and children embark on another year of learning, my thoughts turn to those with clinical conditions that may have an impact on their academic achievement like Attention Deficit Hyperactivity Disorder (ADHD).
ADHD, characterised by chronic levels of inattention, impulsiveness and hyperactivity, affects a significant number of children. It can result in long-term social, academic and mental health problems. The exact cause is not fully understood, but is thought to be a complex interaction between genetic and non-genetic factors. Pharmaceutical treatments are well established, but some children experience side effects and there is concern about their long term effects. Dietary changes have therefore been investigated for some time as an alternative way of reducing symptoms in children with ADHD. This has occurred in parallel with a growing scientific and public interest in the relationship between children’s diet and their mental and physical health.
The association between diet and behaviour, explored in a recent editorial in Journal of Child Psychology and Psychiatry, has both its strong promoters and strong sceptics. Is such strong scepticism unfounded – after all, even if the science supporting diet and poor behaviour is limited, surely improving the quality of children’s diet should be encouraged? The concern is not with a general healthy eating approach, but rather that a rigid parental belief in dietary factors as the exclusive cause of the behavioural issues may act as a barrier to more evidence-based and appropriate treatment.
However, both ends of the extreme – a strong scepticism that dietary factors can have any impact on behaviour and the belief that dietary factors explain all behaviours – are not helpful. Rather we require large well conducted clinical trials to see the strength of evidence of the effects of, for example, supplementation or dietary exclusions. It is this evidence, rather than belief, that needs to be conveyed to clinicians, carers and parents alike.
What is the history and current standing of the diet behaviour hypothesis?
The theory that artificial food additives may contribute to hyperactivity in children was first championed by Benjamin Feingold in the early 1970s. His work was based on a presumed link between increases in the prevalence of behavioural problems – in particular childhood hyperactivity – and the growing presence of synthetic flavours and colours in the western diet. This idea led to the promotion of an exclusion diet which involved the removal of artificial colours and flavours, along with certain natural substances containing salicylates (e.g. certain fruits), also thought to provoke hyperactivity. Subsequently, although remaining popular with some parents and self-help groups, support from health professionals waned. The mainstream clinical approach did not recognise diet as a major element in the causes of ADHD, although in individual cases, where for instance a food allergy was present, it might be important.
Artificial food colour exclusion
In recent years, exclusion diets are enjoying a revival to a degree. A review and meta-analyses of randomised controlled trials (Stephenson et al. 2014) investigating artificial food colour exclusions for the treatment of ADHD suggested a small but significant effect on ADHD symptoms. However, the effect of the size remains uncertain, as does the type of child for whom it is likely to be effective, and the quality of studies that the review is based on are of limited quality making firm conclusions difficult.
Nonetheless, past research funded by the Foods Standards Agency has suggested that consumption of certain artificial food colours could be linked to increased hyperactivity in some children including sunset yellow FCF (E110), quinoline yellow (E104), carmoisine (E122), allura red (E129), tartrazine (E102) and ponceau 4R (E124). A European Union-wide mandatory warning (‘may have an adverse effect on activity and attention in children’) must be put on any food and drink that contains any of these six colours. Many manufacturers and retailers participate in a voluntary ban, and have removed these from their products.
Few Food Diets
Restrictive diets beyond artificial colourings have also been advocated for improvement of behaviour in children with ADHD. Two different approaches are typically cited. The Few Food Diets approach involves the child being placed on an extremely restricted diet (e.g. rice, turkey, vegetables, pears and water). Benefit, if present, is generally noted in 2-3 weeks. New foods are subsequently added one at a time to see whether they are well tolerated or exacerbate symptoms. Alternatively, particular foods that are suspected to exacerbate a child’s behaviour may be removed one at a time to see if behaviour improves. Few studies have attempted to investigate the Few Foods Diet, although in some benefit have been noted on core ADHD symptoms.
However. there are methodological concerns in this research, so results are likely to be biased. In addition a biologically plausible mechanism for the apparent benefit is lacking, as it does not seem to be explainable by an allergic mechanism. Out of two recent meta-analyses, one found an effect size that becomes insignificant when only strictly blinded assessments were made, and in the Stevenson review, the findings for other restrictive elimination diets were less compelling than restricting artificial colours. Additionally, there is little data on how well children accept Few Foods Diets, and it is more a method of identification of diet-sensitive children rather than a treatment.
Sugar and sweeteners
A further popular and long-standing view in the diet and behaviour area is that ‘Western diets’ typified by excess sugar or sweeteners are related to behaviour in children with ADHD or equivalent diagnosis. Overall studies that have investigated sugars or sweeteners versus a control, or sugars compared to sweeteners in children with ADHD, or in children described by their parents to respond adversely to sugars, found no significant effects in core ADHD symptoms. These studies are fairly old, had few participants and only assessed short term exposure. However despite these limitations, current literature does not suggest sugars or any other sweetener causes symptoms of ADHD in children.
Vitamin and mineral supplements
The story regarding dietary supplements for behavioural problems is no less fascinating. A possible role for dietary deficiencies in ADHD has been highlighted in the past. The evidence for micronutrient supplementation remains sparse and inconsistent, partly due to a lack of good quality trials. Many trials have used mega doses of vitamins, and overall there is no evidence that this ameliorates ADHD symptoms, and consideration needs to be given to the potential of toxicity from high dose supplementation. There is also a lack of evidence to recommend routine supplementation of zinc or iron, although there may be some benefit in children with low blood concentrations of zinc or iron-deficiency anaemia.
Polyunsaturated fatty acids (omega-3) supplements
There is evidence that ADHD is associated with deficiencies of polyunsaturated fatty acids (PUFA) and, in particular, omega-3 PUFA; therefore theoretically supplementation may improve ADHD symptoms. Despite a number of relatively new and large intervention studies on this topic there is still no conclusive evidence for this effect, and a 2012 Cochrane review (perhaps considered the gold standard of scientific evidence) concluded that although there were some limited data that indicated there may be some improvement, overall there was little evidence that PUFA supplementation is beneficial. More recent systematic reviews have identified a small but nonetheless significant benefit, though. Given the small size of the beneficial effect reported, there is no suggestion at present that PUFA supplementation should be considered a front-line treatment for ADHD but its use as an adjunct to other more mainline treatments may be worthy of further consideration.
So what can we conclude?
- Robust trials in diet and ADHD are difficult and the methodology of most studies on which systematic reviews are based on are weak
- Clinical significance is difficult to quantify when studies have been undertaken looking at behaviour in children with ADHD who have specific dietary sensitivities (not applicable to all children with ADHD) and in general populations (not necessarily applicable to children with ADHD)
- There is some evidence that supplementation with fatty acids may be useful as an additional therapy, but for other supplements more studies must be conducted before conclusions can be made on their value in reducing ADHD symptoms.
- Restricted elimination diets may be of benefit in certain children, but large scale studies are needed on unselected children using blind assessment and including assessment of long-term outcome to understand the size of effect and relevance to children with ADHD. In addition, elimination diets should be conducted under the auspices of clinical professionals to avoid nutritional deficiencies and to ensure that any possible food allergies or intolerances may be identified.
Increasing research is allowing us to start to disentangle myth from reality with regard to the effect of diet on children’s behaviour. Perhaps the reality in ADHD is that there may be a limited but nonetheless significant role of diet. However, based on the science that we have to date we should beware of fierce advocates of the diet-behaviour relationship overplaying the impact.
Ayela Spiro, British Nutrition Foundation – QCS Expert Nutrition Contributor
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