Does Fish Oil Interfere with Vitamin D? may earn compensation through affiliate links in this story.
Fish oil

Fish oil, such as cod liver oil, has been used as a safe dietary supplement for many generations. Fish oil contains numerous essential nutrients, especially omega-3 fatty acids and vitamins A and D. The vitamin D in fish oil is well absorbed by the body, and other compounds in the oil do not interfere with it. The main concerns about supplementing with fish oil are a potential for vitamin A toxicity and vitamin E depletion. Furthermore, fish oil may interfere or interact with some medications. Consult with your doctor before consuming moderate to high levels of fish oil.

Fish Oil

Fish oil is a supplement made from the fats and/or livers of fish such as cod, salmon, mackerel, herring and sardines. Fish oil, especially cod liver oil, is rich in omega-3 essential fatty acids, an unsaturated fat that displays strong anti-inflammatory properties in the human body. Consequently, fish oil is a popular supplement for people wanting to naturally treat their arthritis and lower their risk of cardiovascular diseases, such as heart attack and stroke. Fish oil is also rich in vitamins A and D. For example, 1 tablespoon of cod liver oil contains about 13,000 international units of vitamin A and 1,300 international units of vitamin D.

Vitamin D

Vitamin D is essential for bone health, hormone regulation, immune response and blood pressure control, among other roles. Your skin produces vitamin D-3 when exposed to specific frequencies of sunlight, although many Americans now avoid the sun for fear of skin cancer, wrinkles or sun spots. Consequently, vitamin D deficiency is fairly common in the United States, where an estimated 70 percent of the population experiences it. Vitamin D toxicity or overdose is not possible from sun exposure, although there is a slight risk of it from consuming too much fish oil because it's fat-soluble and stored in the body. Symptoms of vitamin D toxicity include nausea, reduced bone strength and an increased risk of kidney stones.

Vitamin A Toxicity

Vitamin A is also fat-soluble, but excessive amounts have more of a toxic effect on the body, especially your liver. Since fish oil is rich in vitamin A, consuming large amounts over many weeks or months significantly increases your risk of toxicity symptoms such as nausea, vomiting, appetite loss, dry skin, achy pain, reduced bone mineral density and nervous system disorders. The tolerable upper limit for adults is 10,000 international units of vitamin A daily.

Vitamin E Depletion

The only vitamin that fish oil may interfere with is vitamin E. Some clinical studies have noted that vitamin E levels gradually drop in people who consume fish oil supplements long-term, according to the "Natural Standard Herb & Supplement Reference: Evidence-Based Clinical Reviews." The theory is that absorbing fish oil uses vitamin E, so your body's requirement for the vitamin is greater when taking fish oil supplements. Consequently, taking a vitamin E supplement with fish oil may be a good idea. Consult with a nutritionist about the potential benefits and drawbacks of taking fish oil.

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