Vitamin B6 Safety

Toxicity

Because adverse effects have only been documented from vitamin B₆ supplements and never from food sources, only the supplemental form of vitamin B₆ (pyridoxine) is discussed with respect to safety. Although vitamin B₆ is a water-soluble vitamin and is excreted in the urine, very high doses of pyridoxine over long periods of time may result in painful neurological symptoms known as sensory neuropathy. Symptoms include pain and numbness of the extremities, and in severe cases difficulty walking. Sensory neuropathy typically develops at doses of pyridoxine in excess of 1,000 mg per day. However, there have been a few case reports of individuals who developed sensory neuropathies at doses of less than 500 mg daily over a period of months. None of the studies, in which an objective neurological examination was performed, found evidence of sensory nerve damage at intakes of pyridoxine below 200 mg/day (15). In order to prevent sensory neuropathy in virtually all individuals, the Food and Nutrition Board of the Institute of Medicine set the tolerable upper intake level (UL) for pyridoxine at 100 mg/day for adults (see table below) (4). Because placebo-controlled studies have generally failed to show therapeutic benefits of high doses of pyridoxine, there is little reason to exceed the UL of 100 mg/day.

Tolerable Upper Intake Level (UL) for Vitamin B₆
Age Group	UL (mg/day)
Infants 0-12 months	Not possible to establish*
Children 1-3 years	30
Children 4-8 years	40
Children 9-13 years	60
Adolescents 14-18 years	80
Adults 19 years and older	100

*Source of intake should be from food and formula only.

Drug interactions

Certain medications, interfere with the metabolism of vitamin B₆, and may result in deficiency if individuals taking such medications are not given supplemental vitamin B₆. The anti-tuberculosis medications, isoniazid and cycloserine, the metal chelator, penicillamine, and antiparkinsonian drugs, including L-dopa, form complexes with vitamin B₆, creating a functional deficiency. The efficacy of other medications may be altered by high doses of vitamin B₆. High doses of vitamin B₆ have been found to decrease the efficacy of the anticonvulsants, phenobarbitol and phenytoin, and L-dopa (2, 15).

THE LINUS PAULING INSTITUTE RECOMMENDATION

Metabolic studies suggest that young women require 0.02 mg of vitamin B₆ per gram of protein consumed daily (3, 27, 28). Using the upper boundary for acceptable levels of protein intake for women (100 grams/day), the daily requirement for young women would be calculated at 2.0 mg daily. Older adults may also require at least 2.0 mg/day. For these reasons, the Linus Pauling Institute recommends that all adults consume at least 2.0 mg of vitamin B₆ daily. Following the Linus Pauling Institute recommendation to take a daily multivitamin/mineral supplement containing 100 % of the Daily Value for vitamin B₆ will ensure an intake of at least 2.0 mg/day of vitamin B_6. Although a vitamin B₆ intake of 2.0 mg daily is slightly higher than the most recent RDA, it is 50 times less than the tolerable upper intake level (UL) set by the Food and Nutrition Board.