Carrie Ruxton, PhD RD, Dietitian, Nutritionist, and Health Writer, UK
“Among polyunsaturated fatty acids most scientific evidence on health benefits relates to the very long chain omega-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), with far fewer studies reporting benefits for the shorter-chain alpha-linolenic acid (ALA). Our bodies can metabolize DHA and EPA from the plant-based ALA, but the process is inefficient and can be hindered by high intakes of omega-6 fatty acids. Therefore, it is far more efficient to consume EPA and DHA directly from dietary sources.
Fish is the principal dietary source of omega-3 fatty acids, particularly oily fish, such as salmon, trout, mackerel, herring, and fresh tuna. Meats and fortified products contain small amounts of omega-3 fatty acids, while fish oil supplements are rich in them. Recommendations for omega-3 fatty acids in the UK are presented as ideal weekly fish intakes, i.e. two portions, one of which should be oily (2), which translates as 0.45g per day of omega-3 fatty acids. The fish advice is based on an average portion size of 140g and is meant for the whole population. However, no specific guidelines were given on portion sizes for children, some of whom may struggle to eat 140g. Further policy development is needed to address this gap. In the US, the Food and Nutrition Board suggested around 0.15g per day for pre-school children (3), while the World Health Organization suggested intakes of 0.1-0.25g depending upon the age group (4).
Some authors have attempted to assess omega-3 fatty acid intakes in populations of children. Fish consumption is the best predictor of intake. A study of over 1,000 German children found that daily omega-3 fatty acid intakes in regular fish consumers were ten times higher than in children who ate no fish (0.10-0.26g vs. 0.01-0.02g). In the UK, there are currently no published analyses of intakes in children. However, data on average weekly fish intakes are provided by the National Diet and Nutrition Survey (5,6). It can be seen that younger children consume up to 140g fish per week, while older children consume 116g, but most of this is white fish. Only 14% of pre-schoolers, 10% of young schoolchildren and 6% of teenagers consume oily fish. Even the highest weekly intake of 21g of oily fish in children from ages four to ten would provide just 0.4g omega-3 fatty acids per week – around 13% of the recommended level. These findings are confirmed by a recent telephone survey of 1,000 UK parents: only 10% of children ate fish two or more times a week and 40% ate it once a week, although 42% of parents claimed to be aware of the fish recommendations. In addition, 87% of children never consumed oily fish.
The role of omega-3 fatty acids in the development and maintenance of the human brain has been recognized for some time. DHA makes up 25% of brain fatty acids and seems to drive the rapid growth seen in fetal brain tissue during the last trimester of pregnancy (7). DHA is probably vital for brain development because it creates fluidity in neuronal membranes, thus helping to facilitate enzyme activity, protein binding, and nutrient transport, all of which govern how well the brain functions. DHA also plays a role in the development of vision and accounts for 50% of fatty acids in the retina (8). It is thought that the fluidity of DHA supports the normal functioning of photoreceptor cells, thus helping visual acuity (9). Poor DHA status during fetal development has been linked with sub-optimal cognitive function and vision (10,11). Omega-3 fatty acids also play a role in immune function. Substances in the body called eicosanoids, which are made from fatty acids, control the intensity and duration of inflammatory responses. It is believed that the eicosanoids produced from EPA are less potent, and thus less inflammatory, than those synthesized from omega-6 fatty acids. This means that maternal diets which are high in EPA can program fetal immune systems to be less allergic (12). Several randomized, controlled trials (RCT) have tested how maternal omega-3 status influences infant development. The results from these trials suggest benefits of adequate omega-3 fatty acid intakes to infant development – such as a reduced risk of food allergy (13) and eczema (14), as well as improved mental development (particularly sequential processing and problem solving) (15), eye and hand coordination (16), and visual acuity (clarity) (17) – at maternal intakes of 0.2 to 3.7g of DHA plus EPA per day. These levels are achievable with recommended weekly intakes of fish or regular use of commercially-available fish oil supplements.
Most trials of omega-3 fatty acids in school-aged children have focused on behavioral disorders, such as ADHD (Attention Deficit Hyperactivity Disorder) or dyspraxia (motor learning disability). Generally, omega-3 fatty acid intakes in these trials are 0.3 to 0.6g per day. A systematic review funded by the Food Standards Agency concluded that there were some benefits to supplementing children who had ADHD with omega-3 fatty acids, but also that firm conclusions were hampered by small sample sizes, short studies, and a lack of consistency in dosages (18). Of more relevance is the limited, but growing, number of studies in normal, healthy children. Although most studies found no major impact of supplementation on mental performance tests, some positive effects were found which could, over time, impact on health or performance, e.g. improved DHA/EPA status, more normal immune function (19), better verbal learning and memory (20), and improved performance in listening comprehension and vocabulary acquisition tests (20). Significant reductions of inattention and undesirable behavior in class were also found in the most recent trial (22) using fairly small amounts of omega-3 fatty acids (i.e. 0.01-0.4g/day).
In conclusion, the reviewed study results suggest that omega-3 fatty acids are vital in utero and the first few years of life. Maternal supplementation and supplementation of infants boosts DHA/EPA status and supports the normal development of the brain, the eyes and the immune system. In healthy, school-aged children, the benefits of supplementation are more modest, although results may be hindered by the small number of studies, the limited duration, and low intakes of omega-3 fatty acids. More controlled trials in a greater range of age groups are necessary to determine optimal intakes of omega-3 fatty acids during childhood.”