Omega−3 fatty acids, are polyunsaturated fatty acids (PUFAs), it gets it's name, from the position of the double bond, which is between the third and fourth carbon atoms from the tail end. The three types of omega−3s involved in human physiology are α-linolenic acid (ALA), found in plant oils, and eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), both commonly found in marine oils.
Omega−3 fatty acids are important for normal metabolism. Cells use them to talk to each other.
Docosahexaenoic acid (an omega-3 fatty acid) is essential for proper functioning of adult human brains. Analysis of postmortem liver tissue from Alzheimer’s patients indicates their livers don't make DHA efficiently.