Can You Overdose on B Vitamins?

We all know that vitamins and minerals are healthy for us to consume—but like many things in life, you can have too much of a good thing.

Although the water-soluble family of B vitamins is not as dangerous to consume in excess as the fat-soluble vitamins (A, D, E, and K), there still are risks associated with taking too many B vitamins.

From stomachaches and acne to liver damage and nerve dysfunction, it is possible to see symptoms—ranging from annoying to severe—from taking excessive doses of B vitamin supplements.

In this article, we’ll dive into all the facts about whether or not you can overdose on B vitamin supplements—and how to safely take them to get the benefits without the downsides.

Safe B Vitamin Intake Levels

The Food and Nutrition Board has set either an RDA (Recommended Dietary Allowance) or AI (Adequate Intake) for vitamins and minerals.

The RDA is the average daily intake level of a nutrient to meet the requirements of 97-98% of healthy people. The AI is an intake level assumed to be nutritionally adequate for most people, but the available evidence is not sufficient to develop an RDA.

For the B vitamin family, these are the established RDAs or AIs for adult males and females:

Water-Soluble Vitamins Vs. Fat-Soluble Vitamins

B vitamins (along with vitamin C) are the only water-soluble vitamins—which, if you take your mind back to chem class, means that they dissolve in water upon entering the body and are easily lost in the urine once the body has absorbed or used all that it needs.

Due to this solubility, we cannot store excess amounts of B vitamins for later use—with the exception of vitamin B12, which we’ll get into in a later section. Therefore, B vitamins need to be constantly replenished via diet or supplements. 

Conversely, fat-soluble vitamins (A, D, E, and K) do not dissolve in water (think of mixing oil in water—you can see oil droplets in the fluid, but they don’t blend together) and need dietary fat to absorb.

These vitamins can build up in the body, getting stored in the liver, adipose (fat) tissue, or skeletal muscle (depending on the vitamin).

Side Effects of Excess B Vitamins

While you may have heard the only downside of taking too many water-soluble vitamins is that you’ll have “expensive pee,” several of the eight water-soluble vitamins in the B complex family can cause adverse effects in excess—and some can even be dangerous.

Vitamin B1 (Thiamin)

Vitamin B1, or thiamin, plays an essential role in energy metabolism (helping the body metabolize food into energy), nerve signal conduction, and muscle contraction. 

Thiamin does not have a UL (Tolerable Upper Intake Level), as there is no established toxic level of thiamin. The UL is the maximum intake level of a nutrient that has been determined unlikely to pose a risk of adverse health effects in humans. 

However, the key word is “unlikely”—upper intake levels cannot take into consideration every population and health condition.

The Food and Nutrition Board (FNB) has stated that excessive thiamin consumption might cause adverse effects despite a lack of any strong evidence of toxicity.

As they aptly put it, a lack of a UL does not imply that all humans can tolerate chronic and excessive doses of thiamin (or any nutrient without a UL)—it simply signifies a need for more data. 

Older research from the 1980s determined that excessive thiamin (100 times the Recommended Dietary Allowance of 1.1-1.2 milligrams) taken orally did not cause toxicity. 

While it is unlikely that the general population could overdose on supplemental thiamin, high doses taken orally may cause digestive issues like an upset stomach or nausea. 

However, intravenous thiamin administration—which is used in disorders like Wernicke’s encephalopathy and beriberi (thiamin deficiency)—has been shown to cause hives, lethargy, ataxia (loss of balance and muscle control), itching, and impaired gut motility in small percentages of people. 

Vitamin B2 (Riboflavin)

Vitamin B2—more commonly known as riboflavin—acts as a cofactor to help metabolize carbohydrates, fats, and proteins into cellular energy.

It also has been found to function as an antioxidant, boosting immune function and supporting healthy skin.

Like thiamin, riboflavin does not have an established tolerable upper intake level. 

The digestive system can only absorb a limited amount of riboflavin at a time, so any excess will be quickly excreted in the urine and not absorbed by intestinal cells. 

Studies using large doses of riboflavin (400mg) for three months have not found any adverse effects. For reference, the RDA for riboflavin is just 1.1mg and 1.3mg daily for men and women, respectively.
However, excessive doses of riboflavin may cause harmless orange discoloration in the urine.

Vitamin B3 (Niacin)

Niacin (vitamin B3) is a precursor to NAD+, a coenzyme needed by every one of our cells for energy production, mitochondrial function, and DNA repair. 

We have a Tolerable Upper Intake Level for niacin—for adults over age 19, the UL is set at 35 milligrams per day. 

Despite many beneficial actions, high doses of supplemental niacin (1 to 3 grams per day)—in the form of nicotinic acid—have been shown to cause impaired vision, abdominal pain, high blood sugar, and liver failure. 

High-dose supplemental nicotinic acid can also increase uric acid levels, which is a risk factor for gout.

Other potential side effects of having too much niacin include dizziness, high or low blood pressure, fatigue, headache, and nausea. 

High niacin doses such as these are sometimes prescribed to treat high cholesterol—which it does but at a potential cost. 

Vitamin B3 is also known to cause uncomfortable but harmless skin flushing, tingling, and redness—so much so that the term “niacin flush” has been coined. 

Another form of vitamin B3, nicotinamide (also known as niacinamide), is not known to cause niacin flush or these other reported adverse effects. 

Therefore, keeping your niacin intake to 35mg per day or below is recommended if you take nicotinic acid—otherwise, if it’s nicotinamide/niacinamide, you should be fine at higher doses.

Vitamin B5 (Pantothenic Acid)

Vitamin B5, or pantothenic acid, is involved with cellular energy metabolism and synthesizing the neurotransmitter acetylcholine, which plays a role in muscle contraction, memory, motivation, and learning.

Pantothenic acid is another B vitamin without an established upper limit, as toxicity symptoms have not been observed from high intakes. 

Excessively large doses (15-20 grams per day) can cause an upset stomach and diarrhea, but no other adverse effects have been reported.

For reference, the Adequate Intake recommendation for pantothenic acid is 5mg per day for non-pregnant and non-lactating adults.

Vitamin B6 (Pyridoxine)

Vitamin B6 (pyridoxine) is involved with amino acid metabolism and brain health, as it helps to lower homocysteine levels—an amino acid linked to higher rates of dementia when elevated. It may also reduce the risk of cancer, especially gastrointestinal cancers. 

There is a tolerable upper intake level for vitamin B6—100 milligrams per day for adults—as chronic and excessive consumption can lead to severe neurological symptoms. 

Overdoses of vitamin B6 can cause neuropathy in the hands and feet, unsteady gait, light sensitivity, skin rashes and lesions, nausea, heartburn, ataxia (loss of control of body movements), and impaired reflexes.

Interestingly, the European Food Safety Authority has recently drastically reduced its recommendations for the upper limit for vitamin B6 to just 12 milligrams per day for all adults—but not all scientists are on board with this decision. 

With these serious adverse events, be sure to check the supplements you take—especially if you take several that contain B vitamins—to ensure you are within the recommended amounts and are not overdosing on vitamin B6.

Vitamin B7 (Biotin)

Biotin is well-known for being the “hair, skin, and nails” vitamin, but it also plays a critical role in gene regulation, cell signaling, and promoting the metabolism of fatty acids, glucose, and amino acids. 

There is no UL for biotin, as toxicity of this vitamin has never been reported. 

You may see extremely high doses of biotin in some hair or nail supplements, but your body will simply excrete what it does not need.

However, taking too much biotin is known to cause acne in some people.

Vitamin B9 (Folate)

Folate is crucial for pregnant women to take, as it prevents neural tube defects like spina bifida. However, non-pregnant people still require it for DNA repair, red blood cell formation, and amino acid metabolism.

It also lowers homocysteine, therefore potentially reducing the risk of dementia. However, research has shown that excessive folic acid (the synthetic form of folate) can also negatively affect mental function, in addition to causing insomnia, irritability, and digestive issues.

Plus, taking too much folic acid can mask a vitamin B12 deficiency, which can cause severe symptoms.

This is because folic acid can alleviate a certain type of anemia (megaloblastic anemia) caused by either inadequate B12 or folate intake, but slow and irreversible neurological damage caused by the B12 deficiency can then go undetected. 

Therefore, the UL for folic acid from fortified food or supplements (not including dietary folate in food) is set at 1,000 micrograms (mcg) per day, which is not much higher than the RDA (400mcg for non-pregnant adults and 600mcg during pregnancy).

Vitamin B12 (Cobalamin)

Vitamin B12 is found only in animal foods or fortified foods, and it’s essential for making red blood cells and DNA.

No upper limit has been set for vitamin B12, as there is no established toxic level of intake.

Although vitamin B12 is the only one of the water-soluble vitamins that can be stored in the body (mainly in the liver), it does not appear to accumulate in a negative way. 

However, some evidence suggests that supplements of 20mcg per day or more may increase the risk of bone fractures—especially when combined with excess vitamin B6.

In this study of postmenopausal women, those who took the highest amounts of both vitamins (more than 35mg of vitamin B6 and 20mcg of vitamin B12 per day) had an almost 50% increased risk of hip fractures.

Plus, excessive supplemental B12 can cause breakouts in acne-prone people.

B Vitamin Overdose FAQs