Vitamin B6, also known as pyridoxine, is a water-soluble vitamin that plays an important role in many bodily functions. It is found naturally in many foods and is also available as a dietary supplement. While vitamin B6 is generally safe when consumed in appropriate amounts, taking extremely high doses can lead to vitamin B6 toxicity.
What is vitamin B6 toxicity?
Vitamin B6 toxicity, also known as hypervitaminosis B6, occurs when someone consumes very high amounts of vitamin B6 over an extended period of time. The tolerable upper intake level (UL) for vitamin B6 is 100 mg per day for adults. Consuming more than this over a long period of time increases the risk of toxicity.
Toxicity is more likely to occur from high intake of vitamin B6 supplements, rather than food sources. That’s because supplements often contain much larger amounts of the vitamin than what you could realistically consume from foods alone.
For example, some vitamin B6 supplements provide doses of 200–500 mg or more per serving. Since the body cannot effectively process excess vitamin B6, taking supplements this high greatly raises the risk of adverse side effects.
Symptoms of vitamin B6 toxicity
The symptoms of vitamin B6 toxicity are related to the vitamin’s effects on the nervous system.
Early symptoms may include:
- Tingling or numbness in the hands and feet
- Clumsiness and difficulty walking due to impaired hand-eye coordination
- Nausea
- Abdominal pain
As toxicity progresses, more serious symptoms may develop, such as:
- Painful, unsightly skin lesions
- Patchy hair loss
- Sensitivity to sunlight
- Nerve damage leading to muscle weakness and paralysis
- Impaired nerve signaling between the eyes and brain, causing vision changes
- Mental and emotional disturbances, including depression, confusion, and hallucinations
What causes vitamin B6 toxicity?
The main cause of vitamin B6 toxicity is supplement overdose. While it’s nearly impossible to consume toxic amounts from food sources alone, supplements provide extremely high, concentrated doses.
Other risk factors include:
- Kidney disease: Impaired kidney function reduces vitamin B6 excretion, leading to accumulation in the blood.
- Other medications: Certain drugs like isoniazid, penicillamine, and hydralazine impair vitamin B6 processing, increasing the risk of toxicity.
- Excessively high doses: Doses of just 50–200 mg per day over the long term may cause toxicity in susceptible people.
- Prolonged use: Toxicity occurs with consistent high intake over months or years.
Toxicity effects by dose
The likelihood of vitamin B6 toxicity depends largely on the dose consumed. Higher doses and longer duration of use increase the risk.
| Dose | Toxicity Effects |
|---|---|
| 100–200 mg/day | Possible mild symptoms like tingling in some people |
| 500–1,000 mg/day | Moderate symptoms likely including numbness, pain, and skin lesions |
| Over 2,000 mg/day | Severe toxicity with nerve damage and paralysis |
While doses under 50 mg/day are unlikely to cause adverse effects in most people, those with kidney disorders or taking interacting meds may still be susceptible.
Toxicity diagnosis and testing
If vitamin B6 toxicity is suspected, a doctor can check blood levels of vitamin B6. A pyridoxine level over 100 nmol/L indicates toxicity.
Other diagnostic tests may include:
- Blood counts to check for anemia
- Liver function tests
- Kidney function tests
- Electrocardiogram (EKG or ECG)
- Nerve conduction studies
- MRI or CT scan of the brain
These tests help determine the extent of organ involvement and nerve damage caused by vitamin B6 overload.
Treatment and recovery
The first step in treating vitamin B6 toxicity is to immediately discontinue any supplements and avoid vitamin-fortified foods. No additional vitamin B6 should be consumed until levels normalize.
Treatment focuses on relieving symptoms and may include:
- Medications like gabapentin to reduce nerve pain
- Corticosteroids to decrease inflammation
- Topical creams for skin lesions
- Hair regrowth therapy for hair loss
- Vitamin E supplements to treat associated antioxidant deficiency
In severe cases, hospitalization may be required for pain management, hydration, and nutritional support.
Recovery time depends on the extent of toxicity and nerve damage. Mild cases can resolve within a few weeks of stopping high doses. More severe toxicity may require months to heal, and some nerve damage can be permanent.
Prevention
Vitamin B6 toxicity can be easily prevented by avoiding excessive doses from supplements. Unless advised by a doctor, adults should limit vitamin B6 supplement intake to less than 100 mg per day.
Food sources do not pose a risk for toxicity. Foods high in vitamin B6 include:
- Poultry like chicken and turkey
- Fish like tuna and salmon
- Beef liver and other organ meats
- Potatoes
- Chickpeas
- Fortified breakfast cereals
- Bananas
Getting plenty of vitamin B6 from a balanced diet with a variety of whole foods can help prevent deficiency while avoiding excess intake from supplementation.
Those taking vitamin B6 supplements should also be aware of the vitamin content of any multivitamins or vitamin-enriched foods they consume to avoid inadvertent overdose.
Additionally, anyone with kidney disease or taking medication that affects vitamin B6 metabolism should speak to a doctor before taking B6 supplements, as they are at higher risk of toxicity.
Takeaway
Vitamin B6 toxicity can cause serious nerve damage, skin lesions, vision changes, and other side effects. It is nearly always caused by high-dose supplement overdose over a long period of time.
By sticking to the tolerable upper intake level of 100 mg per day for adults, toxicity can easily be avoided. Food sources do not pose a toxicity risk. While vitamin B6 is important for health, more is not necessarily better, and excessively high doses can do more harm than good.