In the 19th and early 20th centuries, children were often fed a spoonful of cod liver oil, a practice rooted in hundreds of years of folk medicine.

As medical science later confirmed, deriving important nutrients from certain foods is a useful complementary treatment method for certain conditions.

Rickets, a disease caused by a lack of vitamin D in the body, was common prior to the mid-1950s. The disease affected very young children, softening and deforming their bones. They’d outgrow it within a few years. By then, however, permanent damage had already occurred.

Cod liver oil was traditionally used to treat rickets, though scientific evidence that the oil’s high vitamin D content made this treatment effective wasn’t available until the 1930s.

In addition to vitamin D, cod liver oil is also rich in vitamin A, making it very good for the bones, teeth, and eyes. It’s rich in omega-3 fatty acids as well.

Toward the end of the 20th century, researchers began studying fish oil. Unlike cod liver oil, fish oil doesn’t contain vitamins A and D. However, it’s much richer in omega-3 fatty acids than its counterpart. Omega-3s are excellent for heart health — and, as it turns out, for arthritis.

The two types of omega-3 fatty acids found in fish oil are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).

EPA and DHA can reduce inflammation, which causes swelling and pain. has indicated that both acids might suppress the body’s immune system. However, a suggests that DHA might enhance immune function instead. DHA is more effective at reducing inflammation than EPA, but both have a role.

All of these effects makes fish oil potentially beneficial for people with arthritis.

EPA and DHA come with other health benefits: They can help prevent heart attacks by making it harder for blood to clot. They help lower blood triglyceride levels and blood pressure. As well, EPA taken with statin medication is more effective in reducing the inflammation of arteriosclerosis than medication alone.

Cod liver oil is an excellent source of omega-3s, vitamin A, and vitamin D. It’s made from cod livers that are cooked and then pressed.

Fish oil supplements are made from a variety of oily-fleshed, cold-water fish, including mackerel, tuna, herring, salmon, and cod liver. They may also contain whale or seal blubber.

Fish oil contains only a small amount of vitamins and minerals, including iron, calcium, B vitamins, and vitamins A and D.

The term “arthritis” is derived from two Greek words: “arthro,” meaning “joint,” and “itis,” meaning “inflammation.” There are over 100 different types of arthritis, and all of them affect the joints.

The most common is osteoarthritis (OA). It attacks the tough, flexible cartilage in and around the joint. Caused mainly by wear and tear, osteoarthritis generally affects older people.

The second most common form of arthritis is rheumatoid arthritis (RA). RA is a chronic autoimmune disease that causes the immune system to attack the joint’s synovial capsule and other soft tissues. Both types of arthritis cause inflammation and pain in the joints.

For the omega-3 fatty acids in fish oil to work against arthritis, it’s necessary to consume a fairly large quantity of it each day. Fish oil — or cod liver oil — enclosed in capsules makes this fairly easy.

On the other hand, because cod liver oil contains very high amounts of vitamin A and vitamin D, taking too much can be toxic. For the purpose of treating arthritis, fish oil is the safer choice.

Shop for fish oil supplements.

Most people can take even large doses of fish oil without trouble. Nevertheless, some do report mild side effects, including:

Most of these side effects will be reduced or eliminated if you take fish oil immediately before a meal. You can also try freezing the capsules before taking them.

Talk with your doctor before you take fish oil for arthritis, especially in high doses.

It’s important to speak with your doctor if you’re already taking non-steroidal anti-inflammatory drugs (NSAIDs) that suppress the immune system, blood thinners, or blood pressure drugs.

Check with your doctor before taking fish oil with any other alternative or complementary remedies as well. They should be able to advise you about any potential drug interactions.