Why is getting vitamin A from food safer than supplements?

In general, for most people, it's smarter and safer to get vitamin A (and all nutrients, for that matter) from food than from supplements. That's because while it's possible to get all of the nutrients you need from a well-rounded diet, it's unlikely that you'll "overdose" on any one nutrient by eating a variety of foods. However, it's fairly easy to take too much of one nutrient by popping supplements.

Vitamin A is a fat-soluble vitamin, which means that if you consume too much of it, the excess that your body doesn't use right away will be stored, mostly in your liver. (In contrast, excesses of water-soluble vitamins such as vitamin C leave your body in your urine.) For that reason, excess vitamin A can lead to liver damage. High doses of vitamin A can also cause nausea, vomiting, diarrhea, loss of appetite, tiredness, headaches, dizziness, blurred vision, poor muscle coordination, skin itchiness, hair loss, bone pain and increased risk of osteoporosis (the brittle-bone disease). In pregnant women, too much vitamin A may lead to birth defects in the developing fetus. Talk to your doctor before taking vitamin A supplements to make sure that they're safe and recommended for you. Also, be aware that if you eat a lot of liver (chicken or beef), you may be getting too much vitamin A from food. Your doctor can help you figure out if that's the case.
Nutrition & Dietetics
Pre-formed vitamin A can be toxic at high levels (>10,000 IU or 3,000 mcg), thus, unless instructed by a qualified doctor, you would never take a daily supplement or combination of supplements containing anything near this amount. But the point is, this level could be achieved using supplements since the supplement(s) would contain pure pre-formed vitamin A. On the other hand, unless you were eating a very unusual high animal protein diet regularly containing red/organ meats, you would never reach a toxic level of vitamin A from foods. Hypervitaminosis A refers to high storage levels of vitamin A in the body that can lead to toxic symptoms. There are four major adverse effects of hypervitaminosis A: birth defects, liver abnormalities, reduced bone mineral density that may result in osteoporosis and central nervous system disorders. The RDA for vitamin A is 2310 IU and 3000 IU for females and males respectively and it’s important you average this amount daily because vitamin A plays roles in bone growth, immune function, reproduction, vision, cell division important to all parts of the body, etc. Your daily multivitamin and mineral formula (MVM) generally contains 1-2000IUs of pre-formed vitamin A leaving plenty of room for food vitamin A. The remainder of your body’s vitamin A needs will be supplied by a pro-vitamin A source such as beta-carotene from your MVM and fruits and vegetables from your diet. Pro-vitamin A will not be converted to vitamin A unless you body needs it, thus no matter how much pro-vitamin A you consume, you will not reach a toxic level of A. Therefore, the combination of a good MVM and a healthy diet assures no toxicity while delivering the right amount of overall vitamin A.
Dr. Michael Roizen, MD
Internal Medicine
Animal and fish livers are rich in iron and vitamin A, and cod liver oil is often used as a supplement. While very high doses of vitamin A can be toxic, that doesn't typically happen with eating food. Why? It's because the vitamin A comes in a less toxic form in food than in supplements.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.