Omega-3 fatty acids are an essential nutrient, meaning we have to get them from food because the human body doesn’t have the ability to manufacture them out of components. There are three types of omega-3 fatty acids, but the two most important of them—the "long-chain omega-3 fatty acids"—are typically found together in the same source. Humans do have the ability to convert the third kind, called ALA, into one of the long-chain kinds, but the process is not very efficient.
These nutrients serve important functions in the body and play an important role in the brain. One of the long-chain varieties, called DHA, has shown signs of being able to slow or stop dementia. Even in healthy people, insufficient levels of DHA have been found to be associated with "senior moments" and other indicators of mental decline with age; a new study suggests DHA may prevent the loss of brain cells that normally comes with age. The other long-chain omega-3, EPA, helps treat hyperactivity symptoms, and ALA can reduce depression.
DHA does some other tricks as well. It helps inhibit tumor growth in some kinds of cancer, and it can enhance the effectiveness of chemotherapy. There is some evidence that the short-chain ALA can be used to help lower the incidence of coronary heart disease. EPA also buffs chemotherapy, and it can help protect the liver. In addition, EPA’s effect on drugs can help people avoid overdose without compromising the effectiveness of medications used as intended. Both kinds of long-chain omega-3 fatty acids help fight inflammation.
Many people turn to supplements to make sure they get the omega-3 fatty acids they need. Not all supplements deliver what they promise, however. Over-the-counter supplements are lightly if at all regulated in the United States; in many cases, manufacturers don’t even have to prove that the products contain the ingredients in the amounts listed on the label. A recent study found that a lot of fish oil supplements had lower levels of omega-3 acids than labeled—in some cases, a third less. Other studies suggest fish oil supplements may not be as effective as fish oil in fish even when the supplements are accurately labeled.