The Importance of N-3 Fatty Acids in Health and Disease

Interest in the n-3 fatty acids began some thirty years ago from the remarkable studies in the Greenland Eskimo by the Danish scientists, Dyerberg and Bang. These Eskimos had a low prevalence of coronary heart disease despite a high fat diet because their fat contained high proportions of n-3 fatty acids. This discovery stimulated a large amount of subsequent research about n-3 fatty acids as indicated by the several thousand papers that have appeared in the literature. There is little doubt that n-3 fatty acids have a decisive importance in human nutrition. They are significant structural components of the phospholipid membranes of tissues throughout the body and are especially rich in the retina, brain, and spermatozoa in which docosahexaenoic acid (22:6 n-3 or DHA) constitutes up to 36.4 percent of total fatty acids (1,2). These are all structures where membrane fluidity is essential for proper functioning. In the retina, n-3 fatty acids are especially important. N-3 fatty acid deficiency has resulted in decreased vision and abnormalities of the electroretinogram. N-3 fatty acids are essential fatty acids, necessary from conception, throughout pregnancy, in infancy and undoubtedly throughout life. A major question is whether there is need in the human diet for the entire spectrum of n-3 fatty acids from the 18 carbon alpha linolenic acid with three double bonds (18:3 n-3) to the highly polyunsaturated 22:6 n-3 (DHA). Since DHA can be synthesized from 18:3 n-3, is there a need for DRA in infant formulas? Or should DHA be supplied to infant formulas in addition to linolenic acid? DHA is certainly transferred across the placenta to the fetus during pregnancy (3) and it is always present in human milk along with other n-3 fatty acids including linolenic acid. A second question relates to the proper ratio in the diet of the n-6 fatty acids to the n-3 fatty acids. An imbalance in this ratio can accentuate the n-3 fatty acid deficiency state. The n-6/n-3 ratio may have been increased in industrialized societies from the use of vegetable oils rich in the n-6 linoleic acids and from reduced consumption of n-3 rich foods. Since both n-3 and n-6 fatty acids are essential, the ratio of the n-6 fatty acid, arachidonic (20:4) to DHA may be important also. The second important feature of the n-3 fatty acid family is in their role in the prevention and modulation of certain diseases so common in Western civilization. Rather firm evidence is available for certain diseases and less certain evidence, even speculation, about other disorders. A partial listing of such disorders which is by no means complete is provided in table 1.