Taking vitamins is part of the daily routine of millions of people worldwide.
Though directions for safe dosing are listed on most supplement bottles, it’s common practice to take more than what’s recommended.
Consumers are bombarded with health information telling them that taking high doses of certain vitamins can benefit their health in many ways. However, taking too much of some nutrients can be dangerous.
This article reviews the safety of taking vitamins, as well as the side effects and potential risks associated with consuming high doses.
The 13 known vitamins are divided into 2 categories — fat-soluble and water-soluble (
Water-soluble vitamins are readily excreted from the body and not easily stored in tissues. There are more water-soluble vitamins than there are fat-soluble ones (
Water-soluble vitamins include vitamin C, plus eight B vitamins:
- Vitamin B1 (thiamine)
- Vitamin B2 (riboflavin)
- Vitamin B3 (niacin)
- Vitamin B5 (pantothenic acid)
- Vitamin B6 (pyridoxine)
- Vitamin B7 (biotin)
- Vitamin B9 (folate)
- Vitamin B12 (cobalamin)
Because water-soluble vitamins aren’t stored but rather excreted through urine, they’re less likely to cause issues even when taken in high doses.
However, taking megadoses of some water-soluble vitamins can lead to potentially dangerous side effects.
For example, taking very high doses of vitamin B6 can lead to potentially irreversible nerve damage over time, while taking large amounts of niacin — typically in excess of 2 grams per day — can cause liver damage (
Unlike water-soluble vitamins, fat-soluble vitamins do not dissolve in water and are easily stored in your body’s tissues (
There are four fat-soluble vitamins:
- Vitamin A
- Vitamin D
- Vitamin E
- Vitamin K
Given that fat-soluble vitamins can accumulate in the body, these nutrients are more likely to lead to toxicity than water-soluble vitamins.
While rare, taking too much vitamin A, D, or E can lead to potentially harmful side effects (
Alternatively, taking high doses of non-synthetic vitamin K seems to be relatively harmless, which is why an upper intake level (UL) has not been set for this nutrient (
Upper intake levels are set to indicate the maximum dose of a nutrient that’s unlikely to cause harm for nearly all people in a general population (
Water-soluble vitamins are readily excreted from the body, while fat-soluble vitamins can be stored in tissues. Fat-soluble vitamins are more likely to cause toxicity, although water-soluble vitamins can do so as well.
When consumed naturally through foods, these nutrients are unlikely to cause harm, even when consumed in large amounts.
Yet, when taken in concentrated doses in supplement form, it’s easy to take too much, and doing so can lead to negative health outcomes.
Side effects of overconsuming water-soluble vitamins
When taken in excess, some water-soluble vitamins can cause adverse effects, some of which can be dangerous.
However, similarly to vitamin K, certain water-soluble vitamins have no observable toxicity and hence no set UL.
These vitamins include vitamin B1 (thiamine), vitamin B2 (riboflavin), vitamin B5 (pantothenic acid), vitamin B7 (biotin), and vitamin B12 (cobalamin) (
It’s important to note that while these vitamins have no observable toxicity, some of them may interact with medications and interfere with blood testing results. Therefore, caution should be taken with all nutritional supplements.
The following water-soluble vitamins have set ULs, as they can cause adverse side effects when taken in high doses:
- Vitamin C. Although vitamin C has relatively low toxicity, high doses of it can cause gastrointestinal disturbances, including diarrhea, cramps, nausea, and vomiting. Migraines can occur at doses of 6 grams per day (
- Vitamin B3 (niacin). When taken in the form of nicotinic acid, niacin can lead to high blood pressure, abdominal pain, impaired vision, and liver damage when consumed in high doses of 1–3 grams per day (
- Vitamin B6 (pyridoxine). Long-term overconsumption of B6 can cause severe neurological symptoms, skin lesions, sensitivity to light, nausea, and heartburn, with some of these symptoms occurring at intakes of 1–6 grams per day (
- Vitamin B9 (folate). Taking too much folate or folic acid in supplement form may affect mental function, negatively impact the immune system, and mask a potentially severe vitamin B12 deficiency (
Note that these are side effects that healthy people may experience when taking large doses of these vitamins. Individuals with health conditions can experience even more serious reactions to taking too much of a vitamin.
For example, though vitamin C is unlikely to cause toxicity in healthy people, it can lead to tissue damage and fatal heart abnormalities in those with hemochromatosis, an iron storage disorder (
Side effects related to overconsuming fat-soluble vitamins
Because fat-soluble vitamins can accumulate in your body’s tissues, they can cause much more harm when taken at high doses, especially over long periods.
Aside from vitamin K, which has a low potential for toxicity, the remaining three fat-soluble vitamins have a set UL due to their potential to cause harm at high doses.
Here are some side effects related to the overconsumption of fat-soluble vitamins:
- Vitamin A. While vitamin A toxicity, or hypervitaminosis A, can occur from eating vitamin-A-rich foods, it’s mostly associated with supplements. Symptoms include nausea, increased intracranial pressure, coma, and even death (
- Vitamin D. Toxicity from taking high doses of vitamin D supplements can lead to dangerous symptoms, including weight loss, appetite loss, and irregular heartbeat. It can also raise blood calcium levels, which can lead to organ damage (
- Vitamin E. High-dose vitamin E supplements may interfere with blood clotting, cause hemorrhages, and lead to hemorrhagic stroke (
Although vitamin K has a low potential for toxicity, it can interact with certain medications, such as warfarin and antibiotics (
Both water- and fat-soluble vitamins can cause side effects when taken in high doses, with some causing more severe symptoms than others.
Although it’s extremely rare to die from a vitamin overdose, there have been reported instances of death related to vitamin toxicity.
For example, hypervitaminosis A can be caused by taking one large dose of over 200 mg of vitamin A, or chronic use of more than 10 times the recommended daily intake (
Vitamin A toxicity may lead to serious complications, such as increased spinal fluid pressure, coma, and potentially fatal organ damage (
Additionally, taking megadoses of vitamin D — more than 50,000 IU daily — over long periods can lead to high blood levels of calcium (hypercalcemia), which can lead to death (
Overdosing on other vitamins can likewise cause potentially fatal side effects, such as liver damage.
A case report found that taking very high doses of over 5 grams of extended-release niacin can lead to metabolic acidosis, a buildup of acid in body fluids, as well as acute liver failure — both of which can be fatal (
Keep in mind that these potentially deadly side effects are associated with taking exceptionally high doses of vitamins. Even so, caution should always be taken when consuming any dietary supplement.
In rare cases, taking extremely high doses of certain vitamins may lead to fatal complications.
The best way to get the nutrients you need is by consuming a well-rounded diet. However, many people need to supplement with vitamins for a variety of reasons.
Age, genetic disorders, medical conditions, and diet are all factors that can increase the need for certain nutrients.
Fortunately, vitamins are typically safe to take as long as they are used responsibly.
The following chart outlines both the recommended daily intake (RDI) and tolerable upper intake levels (UL) for fat-soluble and water-soluble vitamins (
|RDI for adult men||RDI for adult women||UL|
|Vitamin A||900 mcg retinol activity equivalents (RAE)||700 mcg RAE||3,000 mcg RAE|
|Vitamin B1 (thiamine)||1.2 mg||1.1 mg||No UL established|
|Vitamin B2 (riboflavin)||1.3 mg||1.1 mg||No UL established|
|Vitamin B3 (niacin)||16 mg niacin equivalents (NE)||14 mg NE||35 mg|
|Vitamin B5 (pantothenic acid)||5 mg||5 mg||No UL established|
|Vitamin B6 (pyridoxine)||1.3 mg||1.3 mg||100 mg|
|Vitamin B7 (biotin)||30 mcg||30 mcg||No UL established|
|Vitamin B9 (folate)||400 mcg dietary folate equivalents (DFE)||400 mcg (DFE)||1,000 mcg|
|Vitamin B12 (cobalamin)||2.4 mcg||2.4 mcg||No UL established|
|Vitamin C||90 mg||75 mg||2,000 mg|
|Vitamin D||600 IU||600 IU||4,000 IU|
|Vitamin E||15 mg||15 mg||1,000 mg|
|Vitamin K||120 mcg||90 mcg||No UL established|
Due to potential toxicity, it’s not recommended to consume more than the tolerable upper intake levels set for the nutrients listed above.
Keep in mind that in certain circumstances, your healthcare provider may recommend that you take more than the UL for certain nutrients to correct a deficiency.
For example, vitamin D deficiencies are often treated with high-dose vitamin D injections or supplements that deliver over 50,000 IU of vitamin D, which is much more than the UL (
Though most supplement bottles provide recommendations regarding how much of a vitamin to take per day, needs can vary from person to person.
If you have questions regarding vitamin dosing, it’s best to consult a medical professional.
Some vitamins have set ULs to prevent potential toxicity. It’s best to consult your healthcare provider if have questions regarding proper vitamin dosing.
Although vitamin supplements are safely consumed by many people on a daily basis, it’s possible to take too high of a dose, which can result in adverse side effects.
Overdosing on certain vitamins can lead to serious complications and, in rare circumstances, even death.
For these reasons, it’s important to use vitamins responsibly and consult a trusted health professional if you have questions about proper dosing.