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Fish consumption is of great importance to children’s health and is essential for neurodevelopment, which begins in pregnancy and continues throughout early childhood and into adolescence. However, fish consumption presents conflicting health outcomes associated with its nutritional benefits and its adverse contaminant risks, because both avoiding fish as well as the consumption of contaminated fish can potentially harm children. This may be challenging to communicate. The present review was performed to assess the current knowledge and recommendations around ‘smart’ fish-consumption decisions. Health Canada advises, as well as other advisories and guides, that fish should be consumed for its health benefits, while also informing consumers, especially women and children, to limit certain fish consumption. The current literature must attempt to handle the challenges inherent in communicating the dilemmas of children’s fish consumption. Incorporation of new knowledge translation strategies are proposed as a means to raise the level of knowledge about optimal fish consumption practices.
La consommation de poisson est essentielle pour la santé des enfants et pour le développement neurologique, qui commence pendant la grossesse et se poursuit pendant la petite enfance et l’adolescence. Cependant, les issues de santé liées à ses bienfaits nutritionnels et aux risques néfastes des contaminants qu’il contient sont conflictuels, parce que le fait d’éviter le poisson peut nuire à l’enfant tout autant que la consommation de poisson contaminé. Il peut être difficile de transmettre ce message. Les auteurs ont effectué la présente analyse pour évaluer les connaissances et les recommandations actuelles au sujet des décisions relatives à la consommation « intelligente » de poisson. Les conseils de Santé Canada, de même que d’autres avis et lignes directrices, indiquent qu’il faut consommer du poisson en raison de ses bienfaits pour la santé, mais ils préconisent également aux consommateurs, notamment les femmes et les enfants, de limiter la consommation de certains poissons. Les publications actuelles doivent viser à relever les défis inhérents à la communication des dilemmes liés à la consommation de poisson par les enfants. On propose d’intégrer de nouvelles stratégies de transfert du savoir pour accroître le niveau de connaissances sur les pratiques optimales de consommation de poisson.
For many cultures, fish has been, and still is, an important component of their normal daily diets. Communities rely on fish, which is well recognized for its nutritional benefits as a main source of protein (1). However, reports concerning the health risks of consuming fish have been emerging over the past few decades (2). Contamination of water reservoirs by heavy metals and persistent organic pollutants, such as polychlorinated biphenyls (PCBs), can lead to the contamination of fish, and has been widely investigated for potential detrimental neurological and developmental outcomes that could affect the health of fish consumers (3,4). Currently, some Canadian water reservoirs are polluted and their fish populations contaminated, mainly due to industrial activity. People who eat wild fish are advised to consult the fish consumption advisories provided by Health Canada (Table 1). Furthermore, some retail fish, local or imported, may also be contaminated (Tables 1 and and22).
Publications on the topic of fish consumption may present contradictory messages. The complexity of the topic and the fact that consumption of the same nutritional product is associated with both health benefits and risks presents a challenge for the development, as well as the uptake, of comprehensive, reliable and accessible recommendations for societies to maximize health benefits and, at the same time, minimize risks.
The present review will:
A literature search was performed using the following key words and search phrases: fish consumption, health, children, neurodevelopment, methylmercury, mercury, PCBs, unsaturated fats, omega 3, advisories and guides. The databases searched were the Cochrane Library and PubMed. A general web search was used to identify local advisories and recommendations using the following key words: advisories, mercury, fish consumption, Canada, eat fish and children.
Publications were limited to articles written in English from North America and Europe that included evidence on children’s health risks or benefits associated with the consumption of fish. To describe advisories’ awareness, recommendations and habits of fish consumption, references were limited to Canadian and United States (US) publications and resources, and focused on recent publications (2003 to 2011).
Of more than 700 references identified, more than 200 focused on fish consumption and its related health risks and benefits. Due to publication limitations, only 30 key references are cited in the present review. Approximately 28% of publications on fish guides and advisories referred specifically to children.
Fish is considered to be an important component of human nutrition, is recommended for a balanced diet and contributes to optimal child development (5). Fish is usually grouped together with poultry, meat, eggs and nuts in food guides due to its high protein content. Fish also contains essential vitamins and minerals (eg, selenium [which is associated with the mitigation of the toxic effects of heavy metals], vitamin D and calcium). What makes fish and seafood unique in their nutritive benefits are the low levels of saturated fats and the high levels of the beneficial omega-3 polyunsaturated fatty acids (PUFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are absent from other basic foods.
Most of the research on the benefits of omega-3 PUFAs for development focuses on the effects of exposure during gestation and early childhood. In animal studies, it has been shown that young monkeys that were fed a diet low in omega-3 PUFAs had poor visual acuity and impaired brain function (6). It is believed that omega-3 PUFAs promote fluidity in neuronal cell membranes and help to regulate neurotransmitter activity (6). Furthermore, low maternal seafood intake is associated with increased risk of suboptimal outcomes for prosocial behaviour, fine motor skills, communication and social development scores (7). Additionally, the effects of maternal DHA supplementation or fish consumption on neurodevelopment have been investigated in many human trials, which have assessed a variety of overlapping outcomes, and have suggested that there are many associated benefits to specific neurological domains (eg, mental process, intelligence quotient, improved performance on language tests and visual motor skills), visual acuity and global cognition (8–10). Brain development begins during the prenatal phase and continues through childhood (11). Thus, DHA remains a crucial factor in healthy neurodevelopment and cognition during childhood and even into adolescence (10). Fish consumption by adolescents is associated with better cognition, measured according to academic achievement (12), as well as improved cognitive performance in early adulthood (as a continuous effect related to fish consumption earlier in life ).
Other health benefits, such as reduction of asthma risk, related to consumption of fish or PUFAs during pregnancy, lactation, infancy and childhood have been inconclusive (14). Fish consumption in children has been associated with the prevention of eczema in young children (and not specifically as omega-3 PUFAs) (15).
Intake of supplementary DHA has been suggested to have beneficial effects with regard to immune disorders, such as inflammatory bowel disease, and requires further study (16). Research on the treatment of attention-deficit hyperactivity disorder and other psychiatric disorders with omega-3 and -6 PUFAs has yielded inconsistent evidence (10).
While many of the publications on fish consumption refer only to EPA and DHA supplementation, it is important to recognize the benefits of eating whole fish. Beyond the significance of fish’s benefits on childhood health, it is important to acknowledge the importance of exposing children to healthy dietary patterns that include regular fish consumption. Fish consumption contributes to a reduced risk of cardiovascular diseases in adults (1); therefore, creating smart consumption habits at a young age may affect future dietary habits and health benefits. Higher dietary intake of long-chain omega-3 PUFAs, particularly for boys, and lower intake of saturated fats are required to meet recommendations for prevention of cardiovascular diseases (17). Including fish in the diet may lead to substitution of the saturated fats from meat with the healthier unsaturated fats found in fish, which in the long term may influence various health outcomes, including reducing the risk of cardiovascular disease.
The main health risks associated with eating fish, other than allergies, relate to the potential exposure to contaminants that can be found in fish and seafood. In this context, the most significant risks include exposure to methylmercury (MeHg) and persistent organic pollutants (eg, PCBs) (2,3,9).
Mercury is a heavy metal with high neurological toxic potential, especially when transformed into MeHg in a process that involves metabolism by microorganisms under anaerobic conditions. MeHg binds to proteins, as well as to free amino acids; therefore, MeHg cannot be removed by cooking or cleaning processes that do not destroy muscle tissues (2). A historical example of the toxic properties of mercury was demonstrated in Minamata, Japan in 1956. The people in Minamata were exposed to high levels of mercury that resulted in severe neurological outcomes, which were later described as Minamata disease (18). Later studies confirmed MeHg-induced developmental neurotoxicity, which constituted the basis for risk assessments and related public health policies. Studies report poorer neurological status and slower development in newborns, infants and children exposed to MeHg in utero or during early childhood. According to some reports involving children, MeHg exposure in utero is associated with lower performance on language tests, as well as with attention, memory, and visuospatial and/or motor function deficits (2).
Three longitudinal studies in the Seychelles, New Zealand and Faroe Islands were used to define reference levels of MeHg for risk assessments (3) and investigated the association between prenatal mercury levels and the neurodevelopment and neurobehaviour of children. The New Zealand and Faroe Islands studies found decrements in attention, language verbal memory, motor speed and visuospatial function. The Seychelles study did not replicate these associations. In an attempt to answer these inconsistencies, investigators suggested that adverse effects may become apparent in higher-order, cognitive functions that develop with maturity (2). However, additonal studies in the Seychelles (4) followed mercury exposures in children up to 17 years of age and found no consistent pattern of adverse association between prenatal MeHg exposure and neurocognitive and behavioural outcomes.
In Spain, high mercury levels (0.96 μg/g in hair tests) were associated with cognitive developmental delay in preschool children (19). Oken et al (9) observed associations between high mercury levels and poor child cognition at exposure levels much lower than previously observed, in pregnant women who consumed more than two servings of fish per week, compared with pregnant women who did not consume fish. The current provisional tolerable daily intake (pTDI) of MeHg for women of child bearing age and young children is 0.20 μg/kg/day (11).
There is controversy within the scientific community surrounding mercury’s health effects, as well as the determination of tolerable levels of mercury. Various reports have attempted to evaluate the effects of mercury using mercury levels taken from women’s and children’s blood and/or hair, but these studies have inconsistent findings. Some studies suggest that exposure to the mercury levels tested do not pose a danger and do not support the associations with retarded neurodevelopment, while others show strong associations (3,4,9).
Other contaminants associated with fish consumption are PCBs. PCBs are fat-soluble substances and, therefore, accumulate in fatty tissues. Exposure to PCBs through fish consumption, during fetal development and early life, has been shown to reduce the intelligence quotient and alter the behaviour of children. PCBs have also been associated with immune suppression and alteration of the thyroid gland and the reproductive systems of both men and women, and are also considered to be tumour promoters that enhance the effects of other carcinogenic substances (20). Furthermore, women exposed to PCBs are at high risk of giving birth to infants of low birth weight (20).
The scientific literature acknowledges the need for further research and continues to investigate detrimental health effects attributed to mercury and PCBs to determine their effects on children’s health and safe levels of exposure. Therefore, there is still a need for well-designed research focused on the prenatal period, childhood and adolescence to determine the contribution of dietary fish contaminants (alone or in combination) to adverse effects on neurodevelopment and cognition, which will help the public to weigh the risks and benefits and make an informed decision.
Fish consumption has the potential to affect childhood neurodevelopment in both beneficial and detrimental ways; however, the majority of publications only address either the risks or the benefits. As a result, it is challenging to determine whether the benefits of fish consumtion outweigh the risks, although some researchers have attempted to do so.
While scientists continue to investigate the beneficial properties of fish consumption during childhood, as well as the health effects associated with fish contamination, the question remains: What are the best practices for children’s health – or simply – ‘To eat or not to eat?’ Food guides around the world recommend including fish as an important part of a balanced diet, and various governmental and nongovernmental agencies provide recommendations for eating fish. For example, Health Canada’s fish consumption advice includes recommendations for women and children on fish consumption related to health benefits, as well as advice on fish consumption that should be limited (Tables 2 and and33).
Other online fish consumption guides and advisories are available from both Canadian and US sources (Table 1). Some of these advisories offer more detail, including advice on a long list of fish species, including their different origins, health properties, sustainability considerations and more.
The aim of these guides is to recommend the specific types of fish to be eaten, because different fish have different levels of contaminants and unsaturated fatty acids. Therefore, when choosing fish for consumption, one must be aware of the properties of the fish (eg, fish origin, levels of contaminants and nutritional value) as opposed to considering all fish in a generic fashion. Considering that there are many fish species, it is recommended to use the advisories to learn more about the fish that one consumes, to choose fish with higher levels of omega-3 PUFA (eg, mostly oily fish such as salmon), to avoid or minimize choosing fish with potentially higher levels of contaminants (eg, predatory fish such as shark) and to consume a variety of fish.
Various information sources offer advice and guides for smart fish eating. However, these guides are not always easy to access, especially when information and updates are primarily electronically published or where hard copies, such as updated brochures and guidelines, are less abundant and more difficult to access. Other challenges beyond accessibility relate to the guides’ content, which can be difficult to comprehend and put into action, including multiple considerations for consumers (eg, sustainability considerations) and the identification of health outcomes and relating them to specific types of fish. Most advisories do not provide specific advice for growing and developing children of varying ages, which further delivers uneven messages for health risks and benefits. Additionally, media coverage and public reports, on both the health benefits and the health risks related to fish consumption, that have the bulk of the messaging focused on risks (21) result in confusion, which can leave the consumer in doubt as to the credibility of all sources. These limitations in the available information may lead to indifference, and the disregarding of warnings or, conversely, to minimizing fish consumption altogether. This was demonstrated in a study in which pregnant women who reported improved awareness of fish advisories, also admitted to higher frequencies of fish avoidance (22). Another study found that consumers lacked accurate information on contaminants in fish to make informed risk-balancing decisions (23).
Evaluating fish consumption practices may assist in providing the public with effective fish consumption advice. A survey conducted in Alberta identified lower than recommended consumption of fish by children (24). Hughner et al (25) reported that 250,000 women of childbearing age in the US were exposed to high mercury level fish and that more than two million women did not eat enough fish. From an economic perspective, Shimshack and Ward (26) claim that advisories have net negative benefits because they result in reducing mercury intake at the expense of omega-3 PUFA.
In Vancouver (British Columbia), Innis et al (11) found high levels of mercury in Canadian children from a Chinese cultural background. These children consumed more seafood and fish than other children tested from the same neighbourhoods, and they mostly consumed imported fish that do not appear in the ‘fish to avoid’ category of health advisories. Thus, there is definitely a need to increase the monitoring of more types of fish and to improve the outreach to and education of immigrant populations with respect to the health risks and benefits of fish consumption.
Several studies have demostrated high levels of mercury, obtained from blood and hair tests, in communities around the world. For example, in Ontario, mercury levels obtained from hair were found to be higher than the acceptable level (0.3 μg/g) in women of reproductive age (27). These elevated mercury levels found in Canada stress the need to accurately document fish consumption, as well as the need to understand what shapes consumption habits, so that effective advice, for diverse audiences, can be provided to maximize health benefits and minimize health risks. This advice should include suggestions for safe fish eating and will need to be delivered in a well-designed KT program with outreach to all communities (regardless of education level and accessibility to electronic information).
Many factors affect decisions on fish consumption including awareness of the health benefits and risks, access to guides, availability of fish and cost: “Consumer guidance should therefore be coordinated combining benefit and risk information and be easier to access and easier to understand” (18). Understanding decision-making in the context of fish consumption by children can help in the planning of educational programs that will improve the ability of parents and children to make smart fish-consumption decisions. It will also serve as a preliminary phase for future KT applications, where educational programs will be strictly designed and extensively promoted to address parents’ needs for information and practical advice.
Developing KT strategies to inform the public on MeHg risks and healthy eating habits are challenging for health promoters. Active engagement of public participation in the process of reviewing advisories, as was performed in Alberta (28), will improve the KT process and help achieve good fish consumption habits, where consumers are aware of the health properties of the fish they eat and have the tools to make smart choices.
KT could, and should, be performed directly with consumers, engaging children, youth, parents and caregivers, but KT could also benefit from the engagement of health care providers such as physicians, public health nurses and dieticians. Practitioners are in an ideal position to transfer knowledge and can improve the awareness of parents/guardians and children with respect to making informed choices about fish consumption. Research shows that physicians are considered by the public to be a reliable and trustworthy source for health information (versus the media, governmental advisories, industry, etc) and can clarify the risks and benefits of eating fish (29).
Other suggestions to improve parents’ and caregivers’ knowledge may include: improving dissemination of practical advice (electronically and in hard copy, ie, brochures, fact sheets); distribution of guidelines to various sites (eg, health clinics, retail stores, schools etc); engaging the public and health care providers in the design of advice; and continuous collaboration with the media to release balanced and practical advice.
Alongside KT programs, policy considerations need to take place with respect to better labelling, preventive regulations (eg, strict regulations on pollutant discharge), and reliable monitoring of both local and imported retail fish, as was also suggested by the US Institute of Medicine of the National Academics (18). A study in the US (30) discovered higher than advised levels of mercury in three brands of tuna also available in Canada. This case reaffirms the need for better and more frequent monitoring of all retail fish. Once timely information on the properties of retail and sport fish (ie, their contaminant levels) are available, clearer KT strategies can be applied to formulate meaningful recommendations for the public.
While communicating the health benefits and risks associated with fish consumption remains a challenge, it is important to continue to research and seek new knowledge that will improve and encourage positive behavioural change. The scientific community acknowledges the fact that to sustain health in our society, it is of the utmost importance to promote children’s health. By applying prevention strategies and by promoting knowledgeable, healthy life styles, we will achieve a healthier future society.
The authors thank Covenant Health for supporting this review.