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.
In 2021, there were 42,784 toxic exposures in children in the United States.
Fortunately, most cases do not lead to serious medical outcomes.
Vitamins are a group of essential nutrients vital to keeping your body healthy, 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 (thiamine) 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 vitamin 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.
Some vitamins pose a lower risk of a toxic single dose.
Vitamins 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.
Vitamin A Vitamin A is used to promote vision, the immune system response, and normal organ function when consumed in moderate amounts.
Vitamin A is a fat-soluble vitamin found in high concentrations in animal liver, kidney, and fish oil, and in moderate concentrations in dairy and eggs, sweet potatoes and carrots.
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.
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.
Vitamin A toxicity commonly affects the skin, causing reddening, irritation, and patchy peeling.
Chronic, excessive intake of vitamin A may lead to more severe symptoms, including:
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.
Hypervitaminosis A can result in symptoms such as fatigue, malaise, abdominal discomfort, and more severe manifestations like hepatotoxicity, increased intracranial pressure, and skeletal abnormalities.
Chronic toxicity of high doses of vitamin A, leading to significant health issues.
A unique symptom of excess beta-carotene consumption, called carotenemia, causes a yellow or orange coloration of the skin.
Carotenemia is reversible.
Causes of excess vitamin A
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.
Plant-derived beta-carotene, a provitamin A found in carrots, is metabolized differently than preformed vitamin A and is not found to be responsible for any of the serious symptoms of vitamin A toxicity.
Orlistat, a weight loss medication, decreases the absorption of fat-soluble vitamins including vitamin A.
Retinoids consist of vitamin A-related compounds and are used for treating ailments affecting the skin, blood, and organ lining.
Retinoids may increase the risk of toxicity when taken together with vitamin A supplements.
B Vitamins Most of the B vitamins are important for skin, hair, brain, and muscle health.
With the exception of vitamins B3 and B6, no significant vitamin B toxicity occurs 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.
Vitamin B1 is important for metabolizing glucose and delivering energy to the cells.
Vitamin B2 (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 via the urine and there is no known upper limit for dosage.
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.
High one-time doses of vitamin B3 are not known to be toxic.
B3 should not be taken with 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.
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.
Vitamin B7 may pose a risk to the developing fetus during pregnancy.
Vitamin B9 (Folate, Folic Acid)
Vitamin B9 is important for new cell production as well as early brain and spine development of a fetus during pregnancy.
Vitamin B9 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
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.8 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, 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 naturally in citrus fruit, potatoes, peppers, and greens, and in vitamin C supplements.
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, 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 added to foods such as fortified milk, juice, and cereal. Some people may need to take a vitamin D supplement to get enough.
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 Taking 100 mcg (10,000 IU) or more of vitamin D supplements daily, risks vitamin D toxicity, leading to abnormally high levels of calcium in the blood.
Kidney stones Nausea and vomiting Constipation Excessive thirst Excessive urination Mental confusion Weight loss Taking high doses has also been linked to cancer risk, heart problems, and an increased risk of bone fractures.
Vitamin E, also known as alpha-tocopherol, is a group of eight related compounds that are used as antioxidants to protect the body’s cells from damage.
Vitamin E is found in fish, vegetable oil, nuts, seeds, wheat, and leafy vegetables.
The recommended daily amount for adults is 15 mg.
It also may contribute to the risk of bleeding when taking other medications.
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.
Diagnosis of vitamin D-related symptoms may be done by blood and urine tests for calcium, vitamin D, and phosphorus.
Stopping vitamin D intake is recommended, but other treatments may be needed in severe cases.
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.
Hypervitaminosis is a condition of abnormally high storage levels of vitamins, which can lead to various symptoms as over excitement, irritability, or even toxicity.
Hypervitaminoses are primarily caused by fat-soluble vitamins (D and A), as these are stored by the body for longer than the water-soluble vitamins.
Generally, toxic levels of vitamins stem from high supplement intake and not always from natural sources but rather the mix of natural, derived vitamins and vitamin boosters.
Toxicities of fat-soluble vitamins can also be caused by a large intake of highly fortified foods, but natural food in modest levels rarely deliver extreme or dangerous levels of fat-soluble vitamins.
With few exceptions, like some vitamins from B-complex, hypervitaminosis usually occurs with the fat-soluble vitamins A and D, which are stored, respectively, in the liver and fatty tissues of the body.
These vitamins build up and remain for a longer time in the body than water-soluble vitamins.
Conditions include:
Hypervitaminosis A Hypervitaminosis D Vitamin B3 § Toxicity Megavitamin-B6 syndrome Vitamin E toxicity