Cod liver oil contains two essential vitamins plus healthy omega-3 fatty acids important for cardiovascular health. If you combine cod liver oil with vitamin supplements, you risk developing vitamin poisoning. Cod liver oil's fat-soluble vitamins build up in body tissues if they are not used. While the type of vitamin A in most vitamin supplements only converts to retinol if needed, vitamin D in supplements adds to the dose found in cod liver oil. To be safe, ask your doctor to approve the combination.
Vitamin Content
The potency of cod liver oil varies with the brand, but a high-vitamin product could include 5,000 IU of vitamin A and from 500 to 1,000 IU of vitamin D, says Sally Fallon of the Weston A. Price Foundation. If you're a healthy adult male over 18 years old, you should consume at least 3,000 IU of vitamin A every day. Adult women need only 2,300 IU. Actual daily needs of vitamin D depend partly on the amount of time you spend in the sun. Exposure to ultraviolet light in sunlight generates vitamin D in your skin. If you get little or no UV exposure, you may need from 800 to 1,000 IU daily.
Vitamin A Dangers
An adult man could safely consume as much as 10,000 IU of retinol daily. Chronic over-consumption of retinol, the vitamin A in cod liver oil, causes vitamin A poisoning. Symptoms range from itching, headache and peeling skin to cerebral edema and painful joints. Severe poisoning causes liver damage and potentially fatal illness. Foods such as eggs, butter and milk also contribute to the retinol total. If you eat a normal diet, take cod liver oil, and your vitamin supplement contains retinol, you could easily exceed the safe upper limit. Beta-carotene, found in many vegetables, converts to retinol only as needed, so beta-carotene supplements don't contribute to vitamin A toxicity.
Vitamin D Dangers
Most people need at least 600 IU of vitamin D daily, and if you're over 70 you need at least 800 IU. If you take too much vitamin D, the vitamin could build up in your liver and cause vomiting, weakness and confusion. As the excess raises calcium levels in your blood, your heart rhythm changes and your chances of developing kidney stones increases. Fortified foods also provide vitamin D, as do most multi-vitamin supplements. If you eat a balanced diet and spend a lot of time in the sun, you may already ingest your daily minimum.
Safe Amounts
To be sure you don't consume too much retinol, make beta-carotene the source of half your total intake of vitamin A. If you do exceed the 50 percent retinol goal, your body uses less beta-carotene and you're still within the safe zone. If you eat plenty of kale or collards and enjoy carrots and sweet potatoes regularly, you could already be well supplied with beta-carotene. Your vitamin D needs will vary, since the opportunity for effective sun exposure fades as seasonal lengths of day shorten. If you take enough cod liver oil to provide your daily vitamin D and add another dose through a supplement, you should still be well below the upper limit. Check with your doctor to be sure.
References
- The Weston A. Price Foundation; Cod Liver Oil Basics and Recommendations; Sally Fallon, et al.; February 8, 2009
- Linus Pauling Institute; Mincronutrient Information Center -- Vitamin A; Jane Higdon, Ph.D.; December 2003
- Colorado State University Extension; Fat-Soluble Vitamins; J. Anderson, et al.; August 2008
- MayoClinic.com; What Is Vitamin D Toxicity...; Katherine Zeratsky; December 11, 2010
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