Like every other essential nutrient, your body can't function properly without vitamin A. However, getting too much of the vitamin from certain food sources or vitamin A supplements can be toxic.
Yes, too much vitamin A from supplements and certain food sources, such as liver and cod liver oil, is bad for you.
Vitamin A's Function
Vitamin A is an essential fat-soluble vitamin that supports immune health and reproduction and is critical for vision. Most Americans get an adequate amount of vitamin A to meet their needs, according to the National Institutes of Health (NIH).
The vitamin A in the food you eat is either provitamin A carotenoids, found mostly in plant foods such as carrots and sweet potatoes, or preformed vitamin A, which is found in animal foods like dairy and meat. Your body metabolizes both forms of vitamin A into retinal and retinoic acid. However, to account for the variations in the bioactivity of each form of vitamin A, the recommended dietary allowances (RDAs) for the fat-soluble vitamin are provided as retinol activity equivalents (RAEs).
Your RDA for vitamin A depends on your age and sex. Women need 700 microgram RAEs and men require 900 microgram RAEs. Unlike water-soluble vitamins, like vitamin C and the B vitamins, your body stores fat-soluble vitamins for long periods of time, says the Colorado State University Extension, which is why too much vitamin A is bad. Your body stores excess vitamin A in your liver.
Read more: A List of Vitamins and Their Uses
Too Much Vitamin A
Getting too much vitamin A may lead to a disorder called hypervitaminosis A. The U.S. National Library of Medicine reports that you're unlikely to consume toxic amounts of vitamin A from the food you eat. In most cases, hypervitaminosis A occurs in people taking vitamin A supplements.
How do you know if your vitamin A dosage is too high? The Food and Nutrition Board at the Institute of Medicine developed a tolerable upper limit (UL) for vitamin A to prevent toxicity. The UL for vitamin A for adult men and women is 3,000 microgram RAEs.
It should be noted that the UL for vitamin A dosage specifically refers to animal sources of vitamin A and supplements that contain preformed vitamin A, either as retinol or retinyl ester. Forms of provitamin A carotenoids, such as beta-carotene, aren't likely to lead to hypervitaminosis A. However, beta-carotene supplements aren't recommended except for the treatment of vitamin A deficiency, reports the NIH.
Signs and symptoms that you may be getting a toxic vitamin A dosage include:
- Blurry vision
- Bone pain
- Poor appetite
- Nausea and vomiting
- Itchy, flaky skin
- Yellow skin (jaundice)
High-dose vitamin A supplements may also cause permanent liver damage. Harvard Health Publishing warns that too much vitamin A is bad for your bones and increases your risk of fractures.
The Best Vitamin A Sources
As previously mentioned, most people get an adequate amount of vitamin A from the foods they eat. If you have concerns about getting too much vitamin A, NIH recommends you limit your intake of liver and cod liver oil, which have high concentrations of preformed vitamin A.
For perspective, a 3.5-ounce portion of braised beef liver has 9,363 microgram RAEs, which is more than three times the UL. Eggs are also a source of preformed vitamin A, but one large egg has only 90 microgram RAEs of vitamin A.
Though liver contains high amounts of vitamin A, you don't need to completely cut it from your diet, unless advised to do so by your doctor. However, you should limit the amount of liver you eat every month to reduce risk of toxicity.
To meet your daily needs, you can include these healthy vitamin A sources in your diet:
- Sweet potatoes
- Fortified milk
Though deficiencies are rare, not getting enough vitamin A may cause dry scaly skin or reversible night blindness.
- National Institutes of Health Office of Dietary Supplements: "Vitamin A"
- Colorado State University Extension: "Fat-Soluble Vitamins A, D, E and K"
- U.S. National Library of Medicine: "Hypervitaminosis A"
- The National Academies of Sciences, Engineering, Medicine: "Summary Table: Tolerable Upper Limits"
- Harvard Health Publishing: "Vitamin A and Your Bones"
- USDA FoodData Central: "Beef Liver, Braised"
- USDA FoodData Central: "Eggs, Grade A, Large, Whole Egg"