Vitamin toxicity occurs when you take an excessive amount of a vitamin that is otherwise an essential nutrient needed to keep the body healthy. Sometimes called hypervitaminosis, it can be caused by misuse of vitamin supplements, certain medications and drug interactions, or diet.
Vitamin toxicity is common. For example, in 2021, there were 42,784 toxic exposures in children in the United States. Fortunately, most cases do not lead to serious medical outcomes.
This article explains vitamin toxicity and its causes. It will help you to know how to identify symptoms and make decisions about contacting your healthcare provider or seeking emergency care.
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:
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 these differences in the way vitamins are absorbed and used by the body, some vitamins pose a lower risk of a toxic single 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.
While some diseases and conditions can be helped by elevated vitamin use, complications can occur. Unless advised by a healthcare provider, you should never take more than the recommended daily dosage of multivitamins or vitamin supplements.
Care should always be taken to use only recommended amounts of supplements. Here’s a review of each of the vitamins and the potential risk of vitamin toxicity for each one, including the possible 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). This is 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: 770 mcg RAE
- 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 do need to consume vitamin A but they should avoid high doses during pregnancy or while trying to conceive. Too much vitamin A can lead to developmental disturbances in the embryo/fetus, including the eyes, skull, lungs, and heart.
Symptoms of Vitamin A Toxicity
Vitamin A toxicity commonly affects the skin, causing reddening, irritation, and patchy peeling. Chronic, excessive supplement use may lead to more severe symptoms, including:
- Pressure changes in the skull (intracranial hypertension)
- Vision changes
- Irritability
- Nausea and vomiting
- Dizziness
- Headaches
- Hair loss
- Muscle pain
- Mental confusion
People treated with retinoids can have elevated triglyceride levels that can cause liver damage, bone loss, and other consequences.
A unique symptom of excess beta-carotene consumption, called carotenemia, causes a yellow or orange coloration of the skin, but this condition is reversible and 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 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 fat-soluble vitamin (A, D, E, K) supplements.
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.
B Vitamins
Most of the B vitamins are important for metabolism. They’re important fo 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 (Thiamine)
Vitamin B1, also known as thiamine, is found in beef, pork, whole grains, legumes, nuts, and sunflower seeds. The recommended daily amount for adults is 1.2 milligrams (mg) for men and 1.1 mg for women.
Vitamin B1 is not known to be toxic in high doses. It is important for metabolizing glucose and delivering energy to the cells.
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. It leaves the body quickly when you urinate and there is no known upper limit for dosage.
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 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.
High one-time doses of vitamin B3 are not known to be toxic. However, B3 should not be taken if you have gout as it can increase uric acid levels. When used in combination with statins, there is a higher risk of muscle-related disorders such as rhabdomyolysis, a serious medical condition occurring when damaged muscle tissue releases chemicals into the blood.
B3 may also worsen peptic ulcer disease. 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. However, some research suggests it can pose a risk to the developing fetus during pregnancy. Higher doses also may worsen symptoms of Alzheimer’s disease in older adults.
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. Vitamin B6 is important to infant growth and, later in life, may play a role in managing stress.
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, though it may pose a risk to the developing fetus during pregnancy. There’s also some research to suggest biotin is a factor in sudden infant death syndrome but more study is needed.
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.
Symptoms of B Vitamin Toxicity
Not all B vitamins will lead to symptoms of toxicity at higher doses. 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.
With vitamin B5, some people may experience diarrhea. Extreme doses of vitamin B6 can cause neurological symptoms like numbness and tingling in the extremities. Taking too much may cause loss of coordination, skin lesions, and disrupted digestion.
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.
Symptoms of Vitamin C Toxicity
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.
Symptoms of Vitamin D Toxicity
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:
Taking high doses has also been linked to cancer risk, heart problems, and an increased risk of bone fractures.
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. More study is needed, but there is some evidence that excessive doses can raise the risk of prostate cancer in people with penises. It also may contribute to the risk of bleeding when taking other medications. Talk to your healthcare provider about taking it while receiving cancer treatment.
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 plan to take oral anticoagulants (blood thinners) like Coumadin (warfarin), as they are antagonists.
Treatment
Vitamin toxicity diagnosis and treatment will depend on the specific type. In general, it’s important to stop taking vitamins that play a role in your symptoms but do so while working with a healthcare provider. They may need to change your medications or take other measures, too.
Diagnosis of vitamin D-related symptoms may be done by blood and urine tests for calcium, vitamin D, and phosphorus, for example. Stopping vitamin D intake is recommended, but other treatments may be needed in severe cases. Symptoms of B6 toxicity will usually stop when the vitamin supplements are discontinued, too.
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 most cases, a one-time large dose that leads to acute vitamin A toxicity will occur in children. Inducing vomiting in children is not advised, so contact a healthcare provider or call poison control as soon as possible at 1-800-222-1222.
Summary
Many vitamins pose no threat to your health, even at very high doses. But fat-soluble vitamins, including vitamins A, D, E, and K, can build up to levels that cause symptoms when taken at high doses over long periods of time, or if an underlying health condition or a drug interaction affects how your body is using them. In rare cases, the toxicity may be life-threatening.
Vitamins also can cause toxicity with an excessive single dose. If you are concerned about vitamin toxicity, speak with your healthcare provider about your use of vitamin supplements. They can identify associated symptoms, provide appropriate blood testing, and offer treatment if needed.
As a general rule, simply stopping the overuse of supplements may allow the body to correct the imbalance and restore health.
