The low incidence of
cardiovascular disease in Greenland Eskimos appears to be due to their high intake of seal, whale and fish. The
lipids of these marine animals lower serum
triglyceride and
cholesterol levels and help to prevent blood clotting. The latter effect has been related to a change in the balance of
prostacyclin and
thromboxane as a result of replacing n-6
polyunsaturated fatty acids in the body by n-3
polyunsaturated fatty acids present in marine
lipids. Dietary
fish oils have also been shown to inhibit development of mammary, pancreatic, intestinal and prostatic
tumors in experimental animals. This effect may likewise be due to changes in the production of
prostaglandins or related compounds. The involvement of
prostaglandins and
leukotrienes in immune responses has led to studies on the effects of
fish oil on various
chronic diseases associated with abnormalities of the immune system. Some of these diseases, such as
multiple sclerosis and
psoriasis, are also relatively uncommon in Eskimos. Preliminary results of these studies are encouraging, but more work is required to assess the usefulness of dietary
fish oils in treatment of these diseases. In addition to their apparent therapeutic value,
n-3 fatty acids are considered essential dietary components since they cannot be synthesized in the body and appear necessary for normal vision and probably other body functions.