While there is no disputing that it has many health benefits, you should be aware of the following cautions and potential side effects of cod liver oil.
Cod liver oil may cause nausea, vomiting, decreased appetite, heartburn, stomach bloating, diarrhea, and burping. Some people experience an unpleasant aftertaste from the oil up to several hours after taking the supplement.
Low Blood Pressure
Cod liver oil lowers the blood pressure, which is a good thing if you have high blood pressure, but for people with already low blood pressure, it may lower it too far.
One of the health benefits of cod liver oil is its ability to thin the blood which prevents dangerous blood clots. However, taking large doses of cod liver oil may thin the blood too much and lower the blood’s clotting ability, especially when taken in combination with other blood thinning drugs or supplements such as aspirin, warfarin, heparin, garlic, ginko, and others.
Extreme blood thinning may lead to nose bleeds, bruising, gastric bleeding, or hemorrhagic stroke. If you are taking any other supplements or medications that thin the blood, talk to your doctor before taking cod liver oil.
Some people have reported higher levels of LDL (“bad”) cholesterol after supplementing with large doses of cod liver oil.
Beware of Contaminants
Only purified, high quality cod liver oil should be taken in order to avoid PCBs, dioxins, mercury, and other potential contaminants. Research the brands that are available and find out how they purify their oil before purchasing.
Expectant mothers should be extra aware of the danger of contaminants mentioned above because they may cause birth defects.
Pregnant women should talk to their physician about taking cod liver oil because of its high levels of vitamin A. Large doses of vitamin A during pregnancy have been associated with birth defects. The recommended upper limit of vitamin A is 10,000 IU per day. One tablespoon of cod liver oil may contain as much as 5,000 IU of vitamin A, depending on the brand. Many women opt to take fish oil during pregnancy rather than cod liver oil since the former does not contain as much vitamin A.
One study found that cod liver oil taken during pregnancy increased the risk of gestational hypertension by as much as five times the normal rate. However, it is not clear whether the hypertension was caused by cod liver oil itself or the mercury that may have been present in the oil used in the study.