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The main vitamins in cod liver oil are vitamin A, vitamin D, and the healthy fats eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These are omega-3 fatty acids, which are thought to reduce the inflammation that may contribute to certain health conditions. Vitamin A is needed for proper eyesight and healthy epithelial tissue. Vitamin D is needed by the body to help absorb dietary calcium and maintain bone health.
One tablespoon of cod liver oil contains about 13,000 international units (UI) of vitamin A, which is greater than 250 percent of the dietary reference intake (DRI). Vitamin A deficiency is rare in individuals who take a multivitamin or eat a variety of vegetables.
Vitamin D, another of the vitamins in cod liver oil, occurs at the level of about 1,300 IUs per tablespoon, or about 350 percent of the DRI. Many people are thought to be deficient in vitamin D, particularly the elderly and those who live in northern latitudes. In addition to helping the body regulate calcium intake, vitamin D may prevent some types of cancer, cardiovascular disease, and possibly reduce inflammation.
EPA and DHA are omega-3 fatty acids that may have a number of proposed health benefits, including lowering blood pressure and triglycerides, improving cardiovascular health, and possibly reducing cancer risk. They are also thought to reduce certain conditions marked by an increased inflammation response. One tablespoon contains about 2.5 grams of these fats, which is about twice as much as many fish oil supplements contain.
The vitamins in cod liver oil may interfere with the action of some medications or have a negative effect on an existing condition. Therefore, consult a doctor before taking cod liver oil. When taken in liquid form, the most common dose is one tablespoon daily. Read the manufacturer's instructions when taking cod liver oil supplements in capsules. While unlikely, taking much larger amounts than recommended could result in vitamin A or vitamin D overdose.
Before the advent of synthetic vitamins, the vitamins in cod liver oil played an important role in preventing and treating deficiency diseases caused by inadequate intake of vitamin D and vitamin A. Vitamin A deficiency in developing children can impair vision. The disease called rickets could also be prevented by the vitamins in cod liver oil, as it is caused by low levels of vitamin D. Often beginning at a young age, this condition causes skeletal deformities that persist throughout life.