Cod Liver Oil

Bottom Line: Think twice before taking it. Cod liver oil has some risks, and the benefit is still unproven.

Full article, November 2004:

Was Grandma Right About Cod Liver Oil?

Some of us are old enough to remember when children had to swallow a daily spoonful of cod liver oil (usually against their will) as a vitamin supplement.

Here are some reasons to think twice before taking cod liver oil:

• Though fish oil is rich in heart-healthy omega-3s, supplements can pose dangers. They can increase the risk of hemorrhagic stroke, and people taking anticoagulants should not take them. Large doses may suppress the immune system. The American Heart Association does say that people with heart disease should consider taking the supplements, but only if they don’t eat enough fish and after consulting a doctor. Eating fish is a better option for most people.

• Cod liver oil, bottled or in capsule form, has special problems. It is the richest source of vitamins A and D. Just one teaspoon has 4,500 IU of A, for instance, and the standard dose is one to three teaspoons a day. The capsules contain less oil, but the vitamin can still add up, especially on top of the amount you get from foods and from a multivitamin, if you take one. Recent studies have found that as little as 6,000 IU of vitamin A daily can interfere with bone growth and promote fractures. And women of childbearing age should not exceed 10,000 IU of vitamin A because of the risk of birth defects. Too much vitamin D can also be toxic.

• Cod liver oil is made from livers, of course. The liver is a filter, so toxins (such as PCBs) get concentrated there. Thus cod liver oil is more likely to be contaminated than other fish-oil supplements.

Words to the wise: If you want to see if fish oil helps, eat fatty fish two or three times a week. Even if it turns out that fish oil doesn’t help, there are other known benefits from eating fish. If you want to try the supplements, avoid cod liver oil—and talk to your doctor first.

UC Berkeley Wellness Letter, November 2004