What Is Vitamin Toxicity?

Overuse of supplements may lead to toxic effects in the body

A mix of vitamin capsules, tablets, and gel caps

Verywell / Anastasia Tretiak

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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 onetime 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.

Unless advised by a doctor, you should never take more than the recommended daily dosage of multivitamins or vitamin supplements. While some diseases and conditions can be helped by elevated vitamin use, a healthcare professional should always be consulted before following high-dose vitamin regimens. 

Care should always be taken to use only recommended amounts of supplements. Let’s consider each of the vitamins and the potential risk of vitamin toxicity for each one, 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, often 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 Food and Drug Administration regulations require new product labels to list amounts in micrograms (mcg) RAE.

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 people over age 18: Contraindicated (not recommended) in pregnancy
  • Lactating people: 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 since chronically taking more can be harmful. Pregnant people should avoid ingesting Vitamin A supplements during pregnancy or while trying to conceive, as they can have teratogenic effects, which leads to developmental disturbances of the embryo/fetus.


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.


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 both 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 also take individual liposomal forms of fat-soluble vitamins (A, D, E, K) to replenish what the medication strips from the body.

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.


If you're diagnosed with chronic vitamin A toxicity based on a blood test, the most important course of action is to reduce vitamin A intake. In cases of a large toxic dose, you should take activated charcoal. If activated charcoal isn’t available and a hospital can’t be reached within an hour, use ipecac 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. It's linked to skin, hair, brain, and muscle health. Fortunately, with the exception of vitamins B3 and B6, you most likely will not experience significant vitamin toxicity with their overuse.

Vitamin B1 (Thiamin)

Vitamin B1, also known as thiamin, is found in beef, pork, whole grains, legumes, nuts, and sunflower seeds. The recommended daily amount for adults is 1.2 mg (milligrams) 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, salmon, whole grains, and leafy green vegetables. 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.

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. Make sure to check your cholesterol levels after 30–60 days of a niacin (B3) protocol.

If you're pregnant, avoid taking too much vitamin B3 since it can cause birth defects.

High onetime doses of vitamin B3 are not known to be toxic. However, B3should not be taken if you have gout as it can increase uric acid levels. And when used in combination with statins, there is a higher risk of myopathy, diseases affecting the muscles controlling voluntary body movements, and rhabdomyolysis, a serious medical condition occurring when damaged muscle tissue releases chemicals into the blood. B3 may also  worsen  peptic ulcer disease.

Early symptoms of vitamin B3 toxicity are sometimes called “niacin flush” because it can dilate blood vessels (vasodilation) and lead 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 preexisting liver disease.

Vitamin B5 (Pantothenic acid)

Vitamin B5, also known as pantothenic acid, is found in chicken, egg yolks, 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, which is found in poultry, pork, fish, whole grains, legumes, and blueberries. The recommended daily amount is 1.3 mg–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 mg–6,000 mg taken over an extended period of time can negatively affect the brain, creating neurological symptoms like numbness and tingling in the extremities.

Taking too much 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 people should get 600 mcg, and people 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.

If you take 100 mcg (10,000 IU) or more of vitamin D supplements daily, you risk vitamin D toxicity, leading to abnormally high levels of calcium in the blood. Symptoms may include kidney stones, nausea, recurrent vomiting, constipation, excessive thirst, excessive urination, confusion and weight loss.

Taking high doses has also been linked 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 in which absorption is decreased.

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

Avoid Vitamin K supplementation if you are taking, or plain to take, oral anticoagulants (blood thinners) like Coumadin (warfarin), as they are antagonists.

A Word From Verywell

If you are concerned about vitamin toxicity, speak with your healthcare 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.

7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Olson KR, Anderson IB, Benowitz NL et al. Poisoning and Drug Overdose, Seventh Edition. McGraw-Hill Education / Medical.

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Additional Reading

By Brandon Peters, MD
Brandon Peters, MD, is a board-certified neurologist and sleep medicine specialist.