Cod liver oil is an oil extracted from cod livers. Once commonly given to children daily as a nutritional supplement, it is rarely given today, probably because of its foul taste. Cod liver oil is a significant source of supplemental vitamin A and D; however these vitamins were chemically isolated and packaged in neutral-tasting capsules from the mid 20th century on, eliminating the need to drink the rest of the oil. Now, scientists are discovering that it wasn't just the vitamins in cod liver oil that are healthy, but they say essential fatty acids found in fish oils (such as omega-3) also help brain function.