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Vitamin B6 is the generic name for six compounds with vitamin B6 activity: pyridoxine, pyridoxal, pyridoxamine, pyridoxal 5’ phosphate (PLP) and pyridoxamine 5’ phosphate (PMP). It is a water-soluble vitamin naturally present in many foods, added to others, and available as a supplement.

The functions of vitamin B6 include:

• 100 enzyme reactions, mostly concerned with protein metabolism.
• cognitive development through the biosynthesis of neurotransmitters and in maintaining normal levels of homocysteine.
• gluconeogenesis, glycogenolysis, immune function and haemoglobin formation.

The RDI of vitamin B6 for adults in Australia and New Zealand ranges from 1.3-1.7mg a day.

Potential for vitamin B6 toxicity

The Australian Government Therapeutic Goods Association (TGA) are so concerned about the increase in B6 toxicity, they have released a safety advisory warning of the potential for dose-related adverse events with B6 supplements. 

Read two recent clinical scenarios involving undiagnosed B6 toxicity here

We can assess our clients who have symptoms of peripheral neuropathy for vitamin B6 intake. It presents as tingling, burning or numbness, usually in the hands or feet.

Consider:

• All supplements and combinations being taken
  • B6 by itself, B vitamins, multivitamins and magnesium
• Long-term ingestion of foods or drinks which are fortified with B6
  • Energy drinks can have 2.7mg/100ml, breakfast cereals can have 1.3mg/100g
• Weight loss shakes can have 1mg/serve
• High intakes of vitamin B6 from natural food sources have not been reported to cause adverse effects

Deficiency of vitamin B6 is rare but happens in malabsorption (absorbed in the jejunum), malnutrition and as a side effect of some medications.

Serum B6 deficiency is <20nmol/L, but since deficiency signs and symptoms are seen at 40nmol/L, pathologists suspect the lower limit should be 40 not 20.

Learn more about interpreting standard tests for vitamins and minerals with this Education in Nutrition resource. Read a review here.