An Overview of Vitamin Toxicity

Overuse of supplements may lead to toxic effects in the body

In This Article

Vitamins are essential nutrients that keep the body healthy, but it is possible to have too much of a good thing. Taking an excessive amount of any one vitamin can cause serious health problems, a condition generally referred to as hypervitaminosis, or vitamin toxicity. Certain diet choices may also risk regularly overconsuming vitamins. Misusing vitamin supplements can be very dangerous. Some medications can also increase the risk of vitamin toxicity, either by increasing the body’s absorption of a vitamin or by containing vitamin-based compounds.

In 2017, vitamins were responsible for 59,761 toxic exposures in the United States, 42,553 of which were in children under age 5, as listed by the National Poison Data System. Fortunately, the number of serious medical outcomes associated with vitamin toxicity is much lower. Nevertheless, it is important to recognize the symptoms and understand the causes of vitamin toxicity.

What Are Vitamins?

Vitamins are a group of essential nutrients vital to keeping your body healthy. The right amounts are important to maintain a healthy brain, bones, skin, and blood. Several vitamins also assist in metabolizing food. Many vitamins are not produced by the body and must be obtained through food or vitamin supplements, including:

  • Vitamin A
  • Vitamin B1 (thiamin)
  • Vitamin B2 (riboflavin)
  • Vitamin B3 (niacin)
  • Vitamin B5 (pantothenic acid)
  • Vitamin B6
  • Vitamin B7 (biotin)
  • Vitamin B9 (folate, folic acid)
  • Vitamin B12 (cobalamin)
  • Vitamin C (ascorbic acid)
  • Vitamin D (calciferol)
  • Vitamin E (alpha-tocopherol)
  • Vitamin K (phylloquinone, menadione)

Fat-soluble vs. Water-soluble Vitamins

The main distinction that determines the danger of overdosing is whether a vitamin is fat- or water-soluble. Water-soluble vitamins are used by the body as they are digested and are not usually absorbed in any body tissues for a long period of time. All essential vitamins are water-soluble except for vitamins A, D, E and K. These four are fat-soluble, meaning the body can keep them stored within fat deposits for long-term use. 

Due to the way vitamins are absorbed and used by the body, some vitamins pose a lower risk of a one-time toxic dose. They only cause health problems when taken in high doses continuously for many days or in very extreme doses, usually from misuse of supplements. Fat-soluble vitamins are taken up by the body quickly and can pose immediate health risks when taken in moderate-to-extreme doses.

Multivitamins or vitamin supplements shouldn’t normally be taken in excess of their recommended daily dosage. While some diseases and conditions can be helped by elevated vitamin use, a health care professional should always be consulted before following high-dose vitamin regimens. 

For these reasons, care should be taken to use only the recommended amount of supplements. Let’s consider each of the vitamins and the potential risk of vitamin toxicity for each one.

Consider the most common vitamins and how toxicity may occur if an excessive amount of each is taken, including the potential symptoms, diagnosis, and treatments.

Vitamin A

Vitamin A is used by the body to promote vision, the immune system response, and normal organ function when consumed in moderate amounts. It is a fat-soluble vitamin found in high concentrations in animal liver, kidney, and fish oil, and in moderate concentrations in dairy and eggs. Vegetables such as sweet potatoes and carrots are also moderate sources of vitamin A. 

Animal-based foods contain preformed vitamin A that readily becomes usable by the body through digestion, while plant-based foods often contain carotenoids generically called provitamin A, which can be made into vitamin A in the liver.

The amount of vitamin A in a food or supplement is indicated by retinol activity equivalents (RAE), a measure of how readily the various provitamin A compounds, such as beta-carotene, become vitamin A used by the body. It may also be listed in international units (IU), but FDA regulations require product labels to list amounts in micrograms (mcg) RAE by 2021.

The recommended vitamin A from animal sources and retinoid-based supplements per day varies for different people:

  • Men over age 18: 900 mcg RAE (3,000 IU)
  • Women over age 18: 700 mcg RAE (2,333 IU)
  • Pregnant women over age 18: 770 mcg RAE (2,566 IU)
  • Lactating women: 1,300 mcg RAE

Adults should avoid taking more than 3,000 mcg RAE (10,000 IU). Keeping daily vitamin A intake near the recommended amounts is the safest choice as chronically taking more can be harmful.

Symptoms

Vitamin A toxicity commonly affects the skin, causing reddening, irritation, and patchy peeling. Chronic, excessive supplement use may lead to more severe symptoms, including:

These severe symptoms correspond to lasting effects on bone health and possible liver damage.

A unique symptom of excess beta-carotene consumption, called carotenodermia, causes a yellow or orange coloration of the skin, but this condition is not dangerous.

Causes

Excessive consumption of animal food sources, like liver or fish oil, in addition to supplements high in preformed vitamin A, increases the risk of vitamin A toxicity. Many multivitamins contain vitamin A as a mix of preformed vitamin A and provitamin A, so it is important to identify what kinds are present in these supplements. 

Plant-derived beta-carotene, a provitamin A found in carrots, is metabolized differently than preformed vitamin A. It is not found to be responsible for any of the serious symptoms of vitamin A toxicity.

Some medications will affect how the body absorbs vitamin A. Orlistat, a common weight loss medication, decreases the absorption of fat-soluble vitamins (including vitamin A). Patients taking orlistat should take a multivitamin that includes vitamin A.

Medications called retinoids consist of vitamin A related compounds and are used for treating ailments affecting the skin, blood, and organ lining. These may increase the risk of toxicity when taken together with vitamin A supplements.

Treatment

If chronic vitamin A toxicity is diagnosed based on a blood test, the most important course of action is to reduce vitamin A intake. In cases of a large toxic dose, activated charcoal can be administered. If activated charcoal isn’t available, and a hospital can’t be reached within an hour, ipecac should be used to induce vomiting. In case of a vitamin overdose, poison control should always be contacted as soon as possible at (800) 222-1222.

B Vitamins

Most of the B vitamins are important for metabolism with functions linked to skin, hair, brain, and muscle health. Fortunately, with the exception of vitamins B3 and B6, significant vitamin toxicity is not associated with their overuse.

Vitamin B1 (Thiamin)

Vitamin B1, also known as thiamin, is found in beef, pork, whole grains, legumes, and nuts. The recommended daily amount for adults is 1.2 mg for men and 1.1 mg for women.

Vitamin B1 is not known to be toxic in high doses.

Vitamin B2 (Riboflavin)

Vitamin B2, also known as riboflavin, is found in dairy, eggs, meat, whole grains, and leafy greens. The recommended daily amount for adults is 1.3 mg for men and 1.1 mg for women.

Vitamin B2 has not been shown to be toxic in high doses.

Vitamin B3 (Niacin)

Vitamin B3, also known as niacin, is found in meat, fish, whole grains, and leafy greens. The recommended daily amount for adults is 16 mg for men and 14 mg for women.

High one-time doses of vitamin B3 are not known to be toxic. 

Vitamin B3 is used therapeutically to manage cholesterol. However, people taking it may be at risk of toxicity when taking doses of 50 milligrams (mg) per day or more for a prolonged period of time. Pregnant women should avoid taking too much vitamin B3 as it can cause birth defects.

Early symptoms of vitamin B3 toxicity are sometimes called “niacin flush” due to reddening of the skin, itchiness, and burning. While harmless, it is an important indicator of vitamin B3 toxicity. Prolonged overuse of vitamin B3 can cause liver damage, particularly in people with pre-existing liver disease.

Vitamin B5 (Pantothenic acid)

Vitamin B5, also known as pantothenic acid, is found in chicken, egg yolk, dairy, whole grains, legumes, mushrooms, kale, cabbage, and broccoli. The recommended daily amount for adults is 5 mg. 

Vitamin B5 has not been shown to be toxic in high doses, but in extreme doses may cause diarrhea.

Vitamin B6

Vitamin B6 is a group of compounds related to pyridoxine found in poultry, pork, fish, whole grains, and legumes. The recommended daily amount is 1.3 to 2 mg for adults.

Supplemental doses over 100 mg per day are not recommended for adults outside of therapeutic applications. Extreme doses of 1,000 to 6,000 mg taken over an extended period of time can negatively affect the brain and skin. It may cause loss of coordination, skin lesions, and disrupted digestion. The symptoms usually resolve when the vitamin supplements are discontinued.

Vitamin B7 (Biotin)

Vitamin B7, also known as biotin, is found in liver, pork, eggs, dairy, banana, sweet potato, and nuts. The recommended daily amount for adults is 30 mcg. 

Vitamin B7 has not been shown to be toxic in high doses.

Vitamin B9 (Folate, Folic Acid)

Vitamin B9, commonly known as folate or folic acid, is important for new cell production as well as early brain and spine development of a fetus during pregnancy. It is found in citrus and leafy greens.

The recommended daily amount for adults is 400 mcg. Pregnant woman should get 600 mcg and those who are lactating should get 500 mcg daily.

Folic acid is not generally toxic in high doses, but it can obscure symptoms of pernicious anemia.

Vitamin B12 (Cobalamin)

Vitamin B12, also known as cobalamin, is found in dairy, eggs, fish, poultry, and meat. The recommended daily amount for adults is 2.4 mcg. 

Vitamin B12 has not been shown to be toxic in high doses.

Vitamin C

Vitamin C, also known as ascorbic acid, is used by the body as an antioxidant to prevent damage to cells and also for the growth and repair of tissues in the body. It is found in citrus fruit, potatoes, peppers, and greens. The recommended daily amount for adults is 90 mg for men and 75 mg for women.

Vitamin C is not normally considered toxic, but large doses of 2,000 mg per day can affect digestion, causing diarrhea, cramps, and nausea.

Vitamin D

Vitamin D, also known as calciferol, assists calcium absorption and bone building. Pre-vitamin D can be produced in the skin, but with more people spending the majority of their time indoors or living at latitudes with seasonally reduced sun, sunlit skin alone may not provide all the vitamin D needed. Vitamin D is therefore found in many foods such as fortified milk, fortified juice, cereal, and fish and is available as a supplement.

The recommended daily amount for adults 31 to 70 years old is 15 mcg (600 IU) and 20 mcg (800 IU) for adults 71 and older.

Taking 100 mcg (10,000 IU) or more daily as vitamin D supplements may risk vitamin D toxicity, leading to abnormally high levels of calcium in the blood. Symptoms may include kidney stones, nausea, vomiting, constipation, and weight loss. It has also been connected to cancer risk, heart problems, and an increased risk of bone fractures.

Diagnosis may be done by blood and urine tests for calcium, vitamin D, and phosphorus. For treatment, stopping vitamin D intake is recommended, but other treatments may be needed in severe cases.

Vitamin E

Vitamin E, also known as alpha-tocopherol, is a group of eight related compounds used as antioxidants to protect the body’s cells from damage. It is found in fish, vegetable oil, nuts, seeds, wheat, and leafy vegetables.

The recommended daily amount for adults is 15 mg. 

Daily use of 300 mg or more from supplements may increase the risks of prostate cancer in men, stroke, and hemorrhages.

Vitamin K

Vitamin K, also known as phylloquinone and menadione, is a fat-soluble vitamin important for blood clotting. It is found in milk, soy oil, and leafy greens. Supplements are not generally needed except in situations where absorption is decreased.

The recommended daily amount for adults is 120 mcg for men and 90 mcg for women.

Vitamin K has not been shown to be toxic in high doses.

A Word From Verywell

If you are concerned about vitamin toxicity, speak with your health care provider about your use of vitamin supplements. It will be possible to identify associated symptoms, and appropriate blood testing and, if needed, treatment can be arranged. As a general rule, simply stopping the overuse of supplements may allow the body to correct the imbalance and restore health.

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Article Sources

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial policy to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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