Cod liver oil is extracted from the liver of the Atlantic cod. According to "Encyclopedia Britannica," cod liver oil is high in vitamins A and D and was used beginning in the 18th century to treat rickets, a softening of the bones due to vitamin D deficiency. Cod liver oil is also high in omega-3 fatty acids. These elevated vitamin levels can cause problems in high doses and can interact with certain medications. Before taking any new dietary supplement, consult with your physician.
Vitamin A Toxicity
Because of the high levels of vitamin A found in cod liver oil, you have a risk of developing vitamin A toxicity. According to the "University of California at Berkeley Wellness Guide to Dietary Supplements," one teaspoon of cod liver oil contains as much as 4,500 international units, or IU, of vitamin A; the standard dose for cod liver oil is one to three teaspoons a day. This is well above the recommended dietary allowances from the Institute of Medicine's Food and Nutrition Board of 3,000 IU for adult males and 2,310 IU for adult females. Hypervitaminosis A, or a toxic level of vitamin A, can cause birth defects, reduced bone density, liver abnormalities and central nervous system disorders. Symptoms can include vomiting and nausea, headaches, blurred vision and a lack of muscle coordination.
Medication Interactions
Cod liver oil can also interact with certain medications and cause health problems. If you take antihypertensive drugs for high blood pressure, taking cod liver oil -- which naturally lowers blood pressure -- can reduce your blood pressure to dangerously low levels. If you take anticoagulants to thin your blood, cod liver oil can make your blood even thinner. It acts as a natural blood thinner and can cause bleeding problems.
Fish Allergies
If you suffer from fish allergies, you should avoid cod liver oil. According to the National Institutes of Health, cod liver oil supplements can cause allergic reactions in people with fish allergies. Although no definitive studies have been done on this possibility, given that cod liver oil supplements contain fish oil, patients with a seafood allergy should take caution before ingesting cod liver oil supplements. They should first consult their physician.
Possible Side Effects
Cod liver oil can produce unpleasant side effects, such as belching, bad breath, nausea, heartburn, loose stools and nosebleeds from its blood thinning properties. The Institutes of Health recommends taking cod liver oil supplements with meals or, if in capsule form, freezing them. Taking these precautions can help reduce some of these side effects. Taking large amounts of cod liver oil can also increase your levels of low-density lipoproteins (LDL), also called "bad cholesterol." Having your physician monitor your cholesterol levels is advised.
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