What vitamins can you overdose on?

Vitamins are essential micronutrients that the body cannot synthesize in sufficient amounts, highlighting their importance in the diet at all life stages. Vitamins can be grouped into two main categories—those which are water-soluble and those which are fat-soluble. Many people think taking too much of a water-soluble vitamin is impossible since, unlike fat-soluble vitamins, water-soluble vitamins are not readily stored in the body, and excess amounts are flushed out of the body in urine. However, overdosing on both water-soluble vitamins in addition to fat-soluble vitamins is a real risk and can result in serious adverse effects, some of which may be irreversible.

What vitamins can you overdose on?

Water-soluble vitamins are not easily stored in the body since they are readily dissolved in water upon consumption into the human body and eliminated in urine. Due to this, humans cannot store excess amounts of water-soluble vitamins, and it would be difficult to overdose on such vitamins. In total, there are nine water-soluble vitamins, which include vitamin C and the B vitamins: thiamine (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), biotin (B7), folate (B9), and cobalamin(B12). While deficiency of any of the water-soluble vitamins can result in a serious clinical syndrome, deficiency of water-soluble vitamins is rare in the United States. Deficiencies of such vitamins, however, may be a presenting feature in alcohol use disorder, malnourishment, or malabsorption syndromes such as short-bowel syndrome due to the removal of the small bowel—the site of absorption of all vitamins. 

Fat-soluble vitamins are easily absorbed in fat upon absorption and stored in the body for future use and include vitamins A, D, E, and K. In the past, deficiencies of these vitamins have been directly correlated with several conditions: night blindness due to vitamin A deficiency, osteomalacia due to vitamin D deficiency, oxidative stress due to vitamin E deficiency, and excessive bleeding or hemorrhage due to vitamin K deficiency. 

A well-balanced diet can often avoid the need for dietary supplements. In severe cases of deficiencies, vitamin supplementation is important. However, there can be too much of a good thing. Vitamin overdose of some water-soluble and fat-soluble vitamins beyond their daily recommended doses may result in vitamin toxicity. Awareness of daily recommended doses, maximum dose of a nutrient, and side effects in the setting of vitamin toxicity should be taken into consideration when initiating a vitamin supplement journey. 

Vitamin A 

Vitamin A plays an important role in cell differentiation and turnover in the eyes, salivary glands, and genitourinary tract. It is also a precursor in a cascade of events to promote genes that encode important structural proteins and enzymes throughout the body. Vitamin A can be found in meat, fish, eggs, and dairy products. The body can also convert beta-carotene in certain plant foods into vitamin A. Recommended daily doses of vitamin A in adults are 700 to 900 RAE. Vitamin A levels are tested by measuring serum retinol. Low retinol levels are less than 0.7 micromole/L, while levels greater than 3.5 micromole/L are associated with vitamin A toxicity. 

Vitamin A overdose can present as either an acute toxicity or a chronic toxicity. Acute vitamin A toxicity may result from taking large doses; greater than 100,000 RAE, which are usually accidental Chronic vitamin A toxicity may occur when large doses greater than 30,000 RAE are consistently taken over a long period of time, like months. Signs and symptoms of vitamin A toxicity vary, but headache and rash usually develop during either the acute or chronic phases. Acute toxicity can increase intracranial pressure, resulting in drowsiness, irritability, nausea, and vomiting. Chronic toxicity can present early on as alopecia (hair loss) of eyebrows, skin changes include sparse distribution of hair and dry skin, dry eyes, and chapped lips. Later in chronic toxicity, severe headaches and generalized weakness may develop. Bone changes, including easy fractures, may occur, especially in older people. An additional finding includes an enlarged liver and spleen. Excessive amounts of vitamin A should be avoided in pregnant women as it can result in birth defects. 

Vitamin B 

Vitamin B3, otherwise known as niacin, and its derivatives are vital in cell metabolism. Niacin consumed in large amounts is sometimes used to lower low-density lipoprotein (LDL) cholesterol and triglyceride levels to ultimately increase high-density lipoprotein (HDL) cholesterol levels. While higher doses of niacin-usually exceeding 3,000 mg per day-may reduce LDL cholesterol by up to 20%, it can also cause abdominal pain, vision changes, and hepatotoxicity. Some of these effects can stabilize over time, but individuals with a preexisting liver disorder should avoid high doses of vitamin B3. 

Toxicity can also be experienced when taking greater than 500 mg per day of vitamin B6, otherwise known as pyridoxine. Vitamin B6 and its related compounds are metabolized in the body to serve in important reactions in blood, the central nervous system, and skin metabolism. Long-term overdoses of vitamin B6 can result in adverse effects like low blood pressure, loss of muscle control or coordination, development of painful skin lesions, and sensitivity to light. When ingesting mega doses of vitamin B6, peripheral neuropathy can develop. This may be resolved by stopping vitamin B6 ingestion, but resolution may be slow and incomplete.  

Consuming excess vitamin B9, known as folate or folic acid, can impact mental function as it can hide symptoms of vitamin B12 deficiency until neurological effects become irreversible. 

Vitamin C 

Vitamin C is important in collagen, carnitine, hormone, and amino acid production, which makes it essential for blood vessel health and wound healing. Vitamin C also serves to aid in the absorption of iron and supports the immune system. Doses of vitamin C greater than 2,000 mg/day can cause diarrhea, nausea, and vomiting. In patients with a history of kidney stones, vitamin C supplementation exceeding 1,000 mg/day can increase the risk of kidney stones by up to 40%. Doses up to 10,000 mg per day are sometimes consumed for unproven health benefits. These high doses can result in an overdose, which can cause nausea and vomiting and/or promote iron overload, in turn possibly resulting in irregular heartbeats. 

Vitamin D 

The primary function of vitamin D  is to raise blood levels of calcium and phosphate, which promotes overall bone health. Natural sources of vitamin D are produced by sun exposure, with fortified foods containing small amounts. Therefore, inadequate exposure to sunlight can predispose one to vitamin D deficiency, which can result in diseases of the bone, rickets in children, and osteomalacia or osteoporosis in adults. These disorders may also result from other conditions, including chronic kidney disease, hyperparathyroidism, hypoparathyroidism, insufficient dietary calcium intake, and other disorders or drugs that impair the mineralization of bone structure. 

Many people require supplementation since we don’t get much vitamin D from the sun due to preventive exposure measures in the form of sunscreens or other barriers. Vitamin D has 2 main forms: D2 (ergocalciferol) and D3 (cholecalciferol). Vitamin D supplementation is offered with cholecalciferol since it is more potent than D2. Synthesis of the active metabolite of vitamin D is tightly regulated by intricate pathways in the body, so vitamin D toxicity results from taking excessive amounts of vitamin D supplements. Vitamin D toxicity, also known as hypervitaminosis D, can cause resorption of bone and increased intestinal absorption of calcium resulting in high levels of circulating calcium-a condition known as hypercalcemia. Hypercalcemia can cause nausea, vomiting, weakness, and frequent urination. Prolonged vitamin D toxicity could result in bone pain and kidney problems, including the formation of kidney stones. Serum calcium should be monitored routinely in patients receiving large doses of vitamin D supplementation. 

Vitamin E

Vitamin E is best known for its antioxidant activities, which are substances that protect cells against the effects of radicals. Radicals are molecules produced by the body that could play a role in conditions like heart disease and cancer. Dietary sources include nuts and vegetable oils. There is some research that high doses of vitamin E may slow the progression of Alzheimer’s disease in those diagnosed with mild to moderate Alzheimer’s disease, but this data is not definitive. Additional data suggests that high-dose vitamin E supplementation may benefit those diagnosed with nonalcoholic fatty liver disease, but this has been demonstrated to be associated with the development of insulin resistance. An association between vitamin E deficiency in the first trimester and a risk of preeclampsia, a medical emergency in pregnancy characterized by high blood pressure, has been suggested but not confirmed. Vitamin E supplementation and its impact on cancer, given its antioxidant effects, has been of interest to many researchers, but studies have shown that vitamin E doesn’t prevent cancer and may actually increase the risk of prostate cancer. Large amounts of vitamin E intake (400 to 800 mg/day) usually cause no harm but may cause muscle weakness, fatigue, nausea, and diarrhea, even when consumed long-term. There is also an increased risk of bleeding with these doses, particularly when the dose exceeds 1,000 mg/day, or the patient takes other blood thinning medications like warfarin. Evaluations of previously completed studies have reported that high doses of vitamin E supplementation may increase the risk of hemorrhagic stroke and premature death.  

Vitamin K 

Vitamin K activates specific clotting factors in the liver, which are responsible for coagulation and blood clotting. Vitamin K1, known as phylloquinone, is dietary vitamin K that can be sourced from green, leafy vegetables. Vitamin K1 is not toxic when consumed in the diet, even in large amounts. Vitamin K2 refers to a group of compounds produced by bacteria in the gastrointestinal tract. While vitamin K toxicity is very rare, it is most common in formula-fed infants where it can present as hemolytic anemia and jaundice. In newborns, jaundice can cause kernicterus, which is a form of brain damage.  

Vitamin overdose symptoms 

Most vitamin supplementation can be avoided through a balanced diet rich in all types of vitamins and minerals. Causes of vitamin toxicity may be acute or chronic, with acute ingestions being intentional or accidental, while chronic toxicity occurs due to ingestion over a long time. Acute ingestions usually occur when the specific vitamin is consumed beyond the upper limits of the recommended daily allowance (RDA). Acute ingestions may present differently than chronic overdoses, and symptoms may depend on the specific vitamin. 

Specific adverse effects due to vitamin overdose include the following:

• Vitamin A: nausea and vomiting; changes in skin, hair, and nails; severe headache, increased intracranial pressure, and generalized weakness; spleen and liver damage
• Vitamin B3 (niacin): abdominal discomfort, blurred vision, high blood glucose levels, flushing, and liver damage
• Vitamin B6 (pyridoxine): peripheral neuropathy
• Vitamin B9 (folate): mental changes like irritability and confusion, seizures, skin reactions
• Vitamin C: diarrhea, cramps, migraines, and potentially fatal heart arrhythmias—especially in the setting of iron overload
• Vitamin D: anorexia, nausea, vomiting, increased urination, increased thirst, weakness, nervousness, itching; long-term overdose effects due to increased blood calcium levels include renal failure and metastatic calcifications (especially in the kidneys, as kidney stones)
• Vitamin E: muscle weakness, gastrointestinal disturbances, interference with blood clotting
• Vitamin K: hemolytic anemia, hyperbilirubinemia, and associated jaundice, particularly in impacted infants

Dangers and risks of vitamin overdose

Many short-term side effects of vitamin overdose result in symptoms like gastrointestinal disturbances, changes in liver and kidney function, and some mentation changes. Long term side effects, however, are possible. Peripheral neuropathy development due to vitamin B6 (pyridoxine) overdose may be irreversible, as well as kidney disease or calcifications (like kidney stones) in vitamin D overdose. Excess folic acid consumption can mask severe B12 deficiency until irreversible neurological effects are present. Overdose of vitamin E can impact the body’s ability to clot blood, which can result in bleed-including stroke. Parents should be cognizant of the placement of their daily vitamin supplement bottles to avoid accidental overdose by children, especially when enticing supplements like gummy vitamins are used. 

Vitamin overdose treatment

The most common treatment for vitamin overdoses is to simply stop or modify the daily intake of that vitamin, with the resolution of symptoms anticipated over days to weeks. Accidental overdoses should always be managed by contacting a local Poison Control Center to receive professional medical advice and specific health information. Some overdoses may require specific management under the oversight of a physician. In vitamin D toxicity, intravenous hydration with corticosteroids or bisphosphonates may be prescribed to reduce blood calcium levels.