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At Healthfully, we strive to deliver objective content that is accurate and up-to-date. Our team periodically reviews articles in order to ensure content quality. The sources cited below consist of evidence from peer-reviewed journals, prominent medical organizations, academic associations, and government data.
- Linus Pauling Institute; Vitamin A; Jane Higdon: 2003
- MedlinePlus: Vitamin D
- Office of Dietary Supplements: Vitamin E
- Linus Pauling Institute; Vitamin K; Jane Higdon; May 2004
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Vitamins A, D, E and K are fat-soluble vitamins required in small amounts for good health. Fat-soluble vitamins are stored in the body for a long time until they are needed, and unlike water-soluble vitamins, do not need replacing regularly. Most people meet their vitamin requirements by eating a healthy balanced diet, without the need for vitamin supplements 2. Excess fat-soluble vitamin intake from supplements may cause vitamin levels to build to high levels in the body, which can be toxic and pose a danger to health 2.
Vitamin A is needed for night vision, immune system function, healthy growth and red blood cell production. The recommended dietary allowance for vitamin A for adults19 and older is 900 mcg for males and 700 mcg for females. Vitamin A toxicity is known as hypervitaminosis A and may occur after taking excessive amounts of vitamin A for a long time. Symptoms of too much vitamin A include fatigue, suppressed appetite, nausea, dizziness, headache and dry skin. In severe cases, excess vitamin A may cause liver damage. It also may cause birth defects if taken during pregnancy. The tolerable upper intake level per day for vitamin A is 3,000 mcg for adults, according to the Linus Pauling Institute 13.
Vitamin D controls levels of calcium and phosphorous in the body and helps prevent rickets and osteoporosis. The recommended dietary allowance for vitamin D for people ages 1 to 70 is 600 IU. Taking 4,000 units or more of vitamin D daily may lead to high blood calcium levels. Side effects of excess vitamin D include fatigue, headache, loss of appetite, nausea and vomiting. Too much vitamin D may increase the risk of atherosclerosis in people with kidney disease, and high doses during pregnancy may harm the developing baby, according to MedlinePlus.
Vitamin E is an antioxidant, which means it helps protect the body from damaging free radicals. Free radicals can cause cancer and other diseases. The recommended dietary allowance for vitamin E for people 14 and older is 15 mg. High doses of vitamin E may cause hemorrhage and interfere with blood clotting 2. The tolerable upper intake level per day for vitamin E for adults 19 and older is 1,000 mg, states the Office of Dietary Supplements 2.
Vitamin K is needed for blood clotting. Newborn babies are typically low in vitamin K and are given vitamin K injections at birth to prevent life-threatening vitamin K-deficiency bleeding. The adequate intake for vitamin K for adults 19 and older is 120 mcg for males and 90 mcg for females. There is no risk of toxicity from consuming large amounts of naturally occurring vitamin K, but large doses of synthetic vitamin K may cause damage to cell membranes, liver toxicity, anemia and jaundice. There is no established tolerable upper level of intake for vitamin K, according to the Linus Pauling Institute 13.
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