Food additives, essential nutrients and neurodevelopmental behavioural disorders in children: A brief review
Abstract
In recent decades, changing lifestyles in Canadian homes has led to demand for foods with long shelf lives that are cosmetically appealing, palatable, easy to prepare and to consume. Food additives, especially preservatives and artificial colours as well as suboptimal intake of essential nutrients, have been linked to hyperactive behaviours and poor attention in a subgroup of children. Although other risk factors (ie, genetic, etc) for these conditions have received more attention in the scientific literature, the authors believe that there is enough evidence to consider dietary influences as a modifiable risk factor. This would involve raising awareness among clinicians and, subsequently, reviewing food regulatory processes to better protect children in Canada – similar to the regulations recently undertaken by the British Food Standards Agency. Conflicts of interest due to food and medication industry support for organizations advocating for children would need to be resolved by open communication between government regulatory agencies, academia and industry. Canadian parents and children need to be advised to limit unnecessary food additives and consume a diet rich in essential nutrients while more complete relationships are being explored further.
Résumé
Au cours des dernières décennies, l’évolution des modes de vie dans les domiciles canadiens a suscité une demande d’aliments à longue durée de conservation qui sont visuellement attrayants, de goût agréable et faciles à préparer et à consommer. Les additifs alimentaires, notamment les agents de conservation et les couleurs artificielles, de même qu’une consommation sous-optimale d’éléments nutritifs essentiels, sont liés à des comportements hyperactifs et à un déficit d’attention chez un sous-groupe d’enfants. Même si d’autres facteurs de risque (p. ex., génétiques, etc.) de ces pathologies ont suscité plus d’intérêt dans les publications scientifiques, les auteurs pensons que les données probantes sont suffisantes pour considérer les influences alimentaires comme un facteur de risque modifiable. Il faudrait donc sensibiliser les cliniciens, puis revoir les processus de réglementation des aliments de manière à mieux protéger les enfants du Canada, un peu comme dans la réglementation récente de la British Food Standards Agency. Les conflits d’intérêts causés par le soutien de l’industrie des aliments et des médicaments auprès des organisations qui défendent les enfants devraient être résolus par des communications ouvertes entre les organismes de réglementation gouvernementale, les universités et l’industrie. Les parents et les enfants canadiens ont besoin d’être avisés de limiter l’utilisation d’additifs alimentaires inutiles et de consommer un régime riche en éléments nutritifs essentiels tandis que des relations plus complètes sont explorées.
One challenge associated with the increasingly hectic Canadian family lifestyle is providing children with palatable food options that are easy to prepare and to consume. The food industry has responded seemingly effectively to this challenge by offering foods with long shelf lives, cosmetic appeal and palatability to children by using Health Canada-approved preservatives, food colourings and flavourings. Although these food additives undergo rigorous testing for efficacy and safety, questions are being asked regarding their potential effects on the health and behaviour of children.
In the 1970s, the Feingold diet was introduced following suggestions that hyperactive behaviour demonstrated by children may be managed by eliminating artificial food colours, artificial flavours, naturally occurring salicylates and the preservative butylated hydroxytoluene (1).
Studies from the 1970s and 1980s cautiously supporting the behavioural benefits of diets free from synthetic food dyes and additives (2–4) were counteracted by negative ones (5–7). Small study numbers and inconsistent methodologies noted discrepancies between parental observations and other objective assessments (8–11).
The identification, assessment and management of neurodevelopmental behavioural disorders (NDBDs) in children has become an essential and significant part of paediatric care, not only for the generalists but especially for specialists in the field. The most common NDBD – attention deficit hyperactivity disorder (ADHD) – occurs in 5% to 10% of Canadian children (12) with increased prevalence in First Nations communities (13). The condition persists into adulthood with a prevalence of approximately 4% (14). ADHD is a common diagnosis in children demonstrating delinquent behaviour, school drop out and incarceration (15). NDBDs are multifactorial conditions with an ever-increasing number of potential risk factors – both genetic and environmental (14). ADHD is recognized as a familial disorder in which siblings and parents of children diagnosed with the condition have a two-to eightfold increased risk of developing ADHD themselves. Twin and adoption studies have provided additional support for a genetic predisposition to ADHD. The genetic nature of this disorder is supported by the identification of various susceptibility gene variants in ADHD (16). Environmental risk factors include psychosocial ones (eg, severe marital discord, maternal mental disorder, paternal criminality, foster placement, lower socioeconomic groups and others). Physical and chemical environmental factors include exposure to tobacco smoke and/or alcohol in pregnancy, low birthweight, fetal and childhood exposures to lead, polychlorinated biphenyls (14), arsenic and, potentially, other environmental neurotoxins (17).
Harmful and potentially beneficial dietary implications for ADHD have been studied for several decades with inconsistent findings. Increasing awareness of the implications of ADHD and other NDBDs in childhood for society has led researchers to search for modifiable environmental risk factors.
However, because the condition cannot be satisfactorily explained purely on either genetic or environmental grounds, researchers have directed their attention toward searching for gene-environment interactions in which specific gene variants in individuals may influence the response to various environmental exposures (14).
Clinical and epidemiological evidence supports a potential role of food additives and essential nutrients in NDBD in children as modifiable risk factors for certain symptoms and behaviours.
As a result of ongoing anecdotal evidence, studies focusing on hyperactivity and behavioural problems in childhood in relation to food colouring, flavouring and preservatives continue to be published. A double-blind placebo-controlled study undertaken in 137 three-year-old and 130 eight- or nine-year-old children from the general population (18) supported the theory that artificial colouring and benzoate preservatives promote hyperactive behaviour in children (effect size 0.20 [95% CI 0.10 to 0.39], P=0.044). In addition, meta-analysis data from 15 trials (19) support the notion that artificial food colours promote hyperactivity in children who already suffer from hyperactive syndromes (overall effect size 0.210 [95% CI 0.007 to 0.414]). Similar to other environmentally related disorders in children and, particularly, the subtle neurobehavioural developmental effects for which a multifactorial etiology is proposed, food additives and preservatives warrant further investigation of their safety in vulnerable populations (ie, the fetus and growing young child). Studies repeatedly demonstrate a subgroup of children that responds favourably to withdrawal of food additives from their diet with return of hyperactive behaviours when the food additives are reintroduced (19). Identification of levels of tolerance in these subgroups of children in the context of other mitigating factors may be valuable in the management of their hyperactive behaviours (20). In spite of advances toward understanding the molecular basis of ADHD (21,22), precise knowledge pertaining to how food additives could be contributing to the process is lacking. Experimental evidence indicates that common food additives, in combination, potentiate neurotoxicity, providing support for their potential role in neurodevelopmental alterations (23).
The British Food Standards Agency (24) has already advised parents to eliminate food colourings from the diet of children who exhibit hyperactive behaviours. Review of the regulation of nonessential food additives, taking into account subtle neurodevelopmental symptoms in subpopulations of young children, clearly needs to be undertaken by regulatory agencies. In the meantime, widespread education of health professionals and the community regarding potential links between artificial food colourings and NDBD is essential, especially within institutions that care for these children, and may assist the management of common neurodevelopmental behavioural problems in children. The possibility of reducing medication use, and its potential harmful side effects, in affected children needs to be considered.
Potentially beneficial dietary implications for ADHD similarly need to be addressed. A recent special review article of more than 90 scientific publications (25) summarized evidence of nutritional and dietary influences on ADHD identifying suboptimal levels of certain nutrients in relation to behaviour and learning in children. Children with suboptimal levels of iron, zinc and magnesium may demonstrate improvement in their hyperactivity and attention when supplemented appropriately with these nutrients (25). The results of additional studies (26–28) indicated that supplementing ADHD children with omega-3 fatty acids was associated with improvement of their symptoms, suggesting that deficiency of omega-3 fatty acids may be playing a role in symptoms of ADHD in children.
The challenge ahead lies in identifying the balance between beneficial and potentially harmful dietary factors in subtle neurodevelopmental disorders for which a multifactorial etiology is identified. The British Food Standards Agency (24) considers that there is sufficient scientific evidence to alert parents to potential harmful effects from certain food dyes. Attentions in Canada must focus on reviewing regulatory action that is protective of children. This is a daunting task because organizations caring and advocating for children may be faced with significant conflicts of interest due to support from food and drug companies that market food and medications for children. Raising awareness among clinicians who deal with individual children and families would help move the process forward. Paediatricians could participate in discussions between community, industry, academia and regulatory agencies to develop a plan that includes disseminating available evidence and its shortcomings. Recognizing that, withdrawal of unnecessary food additives and including essential nutrients in the diets of children who exhibit hyperactive behaviours may improve not only their learning, but also their social acceptability; this could be left in the hands of parents to manage but would, ultimately, be more effective if regulated nationally. In the meantime, educating paediatricians about harmful and potentially beneficial dietary implications for ADHD to be included in the general assessment and management of NDBD may not only benefit a small subpopulation of children but also contribute to health promotion aspects of paediatric care. Additional research directed at identifying specific gene variants in children with ADHD and their response to modifiable dietary factors (ie, food additives) may provide valuable evidence for regulators and parents; however, answers will not be available quickly. Improving the diets of children with respect to essential nutrients and non-essential food additives needs to be addressed, and very soon, by society as a whole. This path, in itself, is not an easy one; it demands widespread education, interdisciplinary communication and societal readaptation.
Acknowledgments
The authors thank Bronia Heilik and Susan McRae for their library assistance, Melissa Gibson for her administrative assistance, and Drs Robin Walker and Harold Hoffman for their review of the manuscript.