Long chain polyunsaturated acids from fish are required for the correct development of the brain and retinal in infants and children. In particular, docosahexanoic acid (DHA, C22:6 (n-3)) has been researched with respect to central nervous system growth in early years. Docosahexanoic acid can be synthesised in humans from alpha linolenic acid (ALA, C18:3 (n-3)) and so is not an essential fatty acid. However, conversion of ALA to DHA in humans is slow due to widespread genetic deficiency of the required delta 5-desturase enzyme, and so DHA could be considered conditionally essential, especially during times of accelerated growth during infancy and early childhood. In addition, dietary intakes of ALA are limited to a select number of foods, and Western diets have shifted in recent years to exclude many sources of ALA at the expense on increased intakes of linoleic acid (LA, C18:2 (n-6)).
Because of the importance of DHA for brain and retinal development, researchers have used cross-sectional studies to increase knowledge of the dietary intakes of DHA, particularly in infants and children. One such study published in the Journal of the American College of Nutrition1 investigated the intakes of DHA in Canadian children between 4 and 7 years, using 3 day food records. A total of 78 children completed the study, in which DHA intakes were 37 mg/d. The range in intakes of DHA as an average over 3 days was between 0 and 350mg/d, and per day the range varied between 0 and 991mg/d. The total DHA intakes were less than 30mg/d for 74% of the subjects. The authors also reported that those children not living near marine sources of DHA did not have suitably high intakes of ALA to compensate, with 72% not attaining the recommended intake of ALA.
Taken as a whole, these results suggest that intakes of DHA are higher in marine environments. The fact that dietary intakes of ALA were not high enough to endogenously produce sufficient DHA suggests that children living in non-marine environments may be at risk of impaired growth of important tissues during development, particularly the retina and brain. Where dietary levels of ALA and DHA are low, supplementation with fish oils containing DHA could be a possible solution, as fish oil supplements have been shown to effectively raise plasma levels of DHA. Consuming fatty fish such as mackerel, sardine, trout or salmon 3 times per week is also effective at raising plasma DHA levels, but compliance with eating fish in children may be problematic. The use of ALA from foods such as flax to raise DHA levels is controversial might not be effective.
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