Vitamin B6 Toxicity
National Institute of Health
Food and Nutrition Board (FNB) at the Institute of Medicine of the National Academies (formerly National Academy of Sciences) has established a maximum UL (daily upper limit) of 100 mg/day for adults.
We describe seven adults who had ataxia and severe sensory-nervous-system dysfunction after daily high-level pyridoxine (vitamin B6) consumption. Four were severely disabled; all improved after withdrawal. Weakness was not a feature of this condition, and the central nervous system was clinically spared. Although consumption of large doses of pyridoxine has gained wide public acceptance, this report indicates that it can cause sensory neuropathy or neuronopathy syndromes and that safe guidelines should be established for the use of this widely abused vitamin.
My wife's history of vitamin B6 toxicity.
RDA is 1.5 to 2 mg/day.
My wife's supplements, without consideration of her dietary intake, was 5 mg/d for 2 1/2 years.
The treating dr immediately recognized her symptoms as from B6 toxicity and said it happens frequently.
Half-Life is 15 to 24 days.
A spreadsheet based on bioaccumulation showed that her levels after 2 years and 1/2 could have been equal to around the same as a single dose of 550 mg buildup in her body based on a 80% absorption rate.
A spread sheet that considered bioelimination calculated that her blood levels should return to near normal levels within 6 months. This does not give consideration to her diet which has a substantial number of B6 containing vegetables. After 8 months her symptoms were gone including her peripheral neuropathy.
Many of the supplements on Amazon have from 20 to 100 mg/day of Vitamin B6 and with a half life of 15 to 24 days would allow toxic levels to be obtained with continuous use.
Pyridoxine neuropathy.
A case of sensory neuropathy in a young woman due to long-term ingestion of pyridoxine, with subsequent recovery, is described. Pyridoxine neuropathy may occur after the long-term ingestion of doses as low as 200 mg a day. Because of its widespread use in the community, both the general public and the medical community need to be aware of this recently described complication of megavitamin therapy.
A newly recognised neurotoxic syndrome due to pyridoxine (B6) overdose is described. It is the largest series of B6 intoxication hitherto reported.T A raised serum B6 level was present in 172 women of whom 60% had neurological symptoms, which disappeared when B6 was withdrawn and reappeared in 4 cases when B6 was restarted. The mean dose of B6 in the 103 women with neurological symptoms was 117 +/- 92 mgs, compared with 116.2 +/- 66 mgs in the control group. There was a significant difference (P less than 0.01) in the average duration of ingestion of B6 in the neurotoxic group of 2.9 +/- 1.9 years compared with 1.6 +/- 2.1 years in controls. The symptoms were paraesthesia, hyperaesthesia, bone pains, muscle weakness, numbness and fasciculation, most marked on the extremities and predominantly bilateral unless there was a history of previous trauma to the limb. These women were taking a lower dose of B6 than previously described (1,2), which may account for the complete recovery within 6 months of stopping B6.
Vitamin B-6 toxicity cannot occur from eating natural foods, but it can occur from supplementing with its synthetic form, pyridoxine. The recommended dietary allowance of vitamin B-6 for adults is no more than 2 mg daily, but toxicity is not thought to occur until ingesting at least 100 mg daily, if not 500 mg daily, for many weeks consecutively. Some people do mega-dose pyridoxine for long enough to cause toxicity, which leads to symptoms ranging from temporarily irritating to permanent and disabling.
Vitamin B6 (pyridoxine) causes neuropathy at intakes of 1000 mg per day or more, which is about 800 times the daily intake from foods. There have also been occasional reports of toxicity at intakes of 100-300 mg per day. The US authorities set the no-observed-adverse-effect-level at 200 mg per day and the safe upper limit at 100 mg per day.
Supplementation with pyridoxine at doses greater than 50 mg/d for extended duration may be harmful and should be discouraged.
Because of suppliments and certain medical therapies including some chemotherapies, vitamin B6 toxicity is becoming much more common.
Note - A search of vitamin B6 supplements on Amazon shows that many supplements currently on the market are well above the recommended dietary allowances. The long half life allows for toxic levels to build rapidly.
