KIN 343 - 11.25 Vitamin B6 Toxicity and Excretion

The kidneys are the primary route for excretion of vitamin B6, similar to other water-soluble B vitamins.
Blood levels of vitamin B6 can be regulated by using diuretics, which increase urinary filtration, leading to higher urinary excretion and lower blood levels.

Vitamin B6 supplements are commonly found in pharmacological doses, often around 100 milligrams, which is equal to the tolerable upper intake level (UL).
The rationale behind these high doses is that they may be beneficial in treating various conditions, such as:
- Hyperhomocystinemia
- Carpal tunnel syndrome
- Premenstrual syndrome
- Depression
- Muscle fatigue
- Paresthesia

Unlike many other B vitamins, B6 has an established UL due to potential toxicity at high doses.
Chronic intake above the UL has been linked to nervous system damage.
For comparison, niacin also has a UL, primarily due to mild flushing at lower doses (35-40 mg), while vitamin B6's toxicity can be more severe.

Excess supplemental pyridoxine can lead to:
- Sensory or peripheral neuropathy.
- Symptoms include:
  - Unsteady gait (ataxia)
  - Paresthesia (crawling sensation in extremities, especially when lying down)
  - Impaired tendon reflexes.
Neuropathy can result from degeneration of the dorsal root ganglia in the spinal cord and loss of myelin surrounding peripheral nerves.
As myelin is lost, it can lead to degeneration of sensory fibers and the axons they protect.

The tolerable upper intake level is designed to minimize the risk of neuropathy.
Most individuals consuming 100 mg of vitamin B6 will not experience toxicity; however, exceeding this amount without medical supervision is not advised, as it can result in serious toxic effects.