Influence of fish-oil supplements on man.

Cod-liver oil has been used as a household remedy for centuries and over the course of time scientific explanations for its properties have become available. The first extensive clinical tests of cod-liver oil seem to have been made by Samuel Kay, a physician at the Manchester Infirmary from 1752 to 1784. He gave doses of cod-liver oil to patients suffering from bone diseases and rheumatism and wrote ‘the good effects of it are so well known among the poorer sort that it is particularly requested by them for almost every lameness’. Cod-liver oil played a central role in the isolation and discovery of vitamins A and D because it was known to cure night blindness, corneal xerosis and rickets. The nutritional value of cod-liver oil was officially acknowledged during World War I1 by the Ministry of Food who established a scheme for the free distribution of the oil to all infants up to 5 years old and to pregnant and nursing women. The issue of cod-liver oil by the Ministry of Food had a remarkable effect on the sales of the oil after the war. Indeed, the administration of cod-liver oil to children was widespread until the late 1950s. Cod-liver and halibut-liver oils still remain a popular supplementary source of vitamins A and D. There has been renewed interest in fish-oil supplements since Dyerberg et al. (1978) postulated that dietary eicosapentaenoic acid (20:503; EPA) may offer protection against acute myocardial infarction by way of its influence on blood lipids, prostaglandins and haemostatic function. Fish oil is a readily available source of EPA, consequently fish-oil supplements have been used to evaluate the effect of EPA on blood lipids, haemostasis and eicosanoid production. Different fish oils of varying composition and dose have been used so there are difficulties in extrapolating the results from one study to another. It should be emphasized that fish oils do contain other pharmacologically active ingredients apart from EPA. Most fish oils contain significant amounts of other 0 3 polyunsaturated fatty acids such as docosahexaenoic acid (22:603; DHA), which shares several of the pharmacological effects of EPA (Corey et al. 1983), and so there is no justification in attributing all the effects observed with fish-oil supplements to EPA. The fatty acid composition of fish oil varies considerably from species to species and seasonally (Ackman, 1982) and is dependent on the food chain. As a rule fish oils from cold-water fish contain high proportions of 0 3 fatty acids, mainly EPA and DHA with smaller amounts of 18:403 and 22:503. The oils from certain tropical fish contain a relatively high proportion of arachidonic acid (20:406; AA) (O’Dea & Sinclair, 1982). Generally, fish-liver oils contain high levels of vitamins A and D, the highest concentrations being found in sharkand halibut-liver oil. Oils extracted from the crushed whole fish such as anchovy, sardine and menhaden oil contain far lower