Fish oils

General information

Omega-3 fatty acids are long-chain polyunsaturated fatty acids. The parent fatty acid of this group is alpha-linolenic acid, an essential fatty acid that the body is unable to synthesize; alpha-linolenic acid can be converted in the body to eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). In animals and man, these acids reduce the production of several compounds that are involved in inflammation and thrombosis, such as eicosanoids (prostaglandins, thromboxanes, prostacyclin, and leukotrienes) and cytokines (interleukin II-1) [ ]. The extent of the conversion of alpha-linolenic acid to EPA and DHA is unclear. The conversion process appears to be inhibited by a high intake of linoleic acid, another essential fatty acid [ ]. In addition, alpha-linolenic acid is found in dark green vegetables and the oils of certain nuts and seeds, especially rape seeds and soya beans.

Oily fish and extracted fish oils contain high concentrations of EPA and DHA. Fish oils also contain vitamins A and D. Oil derived from cod, halibut, or shark liver, or from fish body, typically contains about 200 mg/ml of long-chain omega-3 fatty acids. In addition, cod liver oil provides 50 micrograms/ml of vitamin A and 2 micrograms/ml of vitamin D. Many fish oil supplements are artificially enriched with omega-3 fatty acids.

The safety of drugs containing EPA and DHA has been reviewed; the reported adverse reactions were similar to those in control groups [ ]. Even 3–7 g/day for several months did not change liver enzyme activities, and there were no bleeding problems. Consumption of fish oils reduces the resistance of LDL to oxidative modification, and this is partly opposed by the addition of vitamin E [ ]. Belching or eructation with a fishy taste or smell, vomiting, flatulence, diarrhea, and constipation are relatively common.

Organs and systems