Vitamin B6 Blood Test: Normal Ranges, Causes & What Your Results Mean

What Is Vitamin B6?

Vitamin B6 is a group of six related compounds (pyridoxine, pyridoxal, pyridoxamine, and their phosphorylated forms) that the body converts to the active coenzyme pyridoxal 5'-phosphate (PLP). PLP is involved in over 150 enzymatic reactions — more than any other coenzyme — making B6 one of the most versatile vitamins in human biochemistry.

B6 is essential for amino acid metabolism, neurotransmitter synthesis (serotonin, dopamine, GABA, noradrenaline), haemoglobin formation, immune function, and the conversion of stored glycogen to glucose for energy. It also helps regulate homocysteine levels — an amino acid linked to cardiovascular disease when elevated.

Why Is Vitamin B6 Tested?

• Investigate symptoms of deficiency: peripheral neuropathy, dermatitis, glossitis, confusion, or depression
• Evaluate elevated homocysteine levels — B6, B12, and folate all help metabolise homocysteine
• Assess nutritional status in patients with restricted diets or malabsorption
• Investigate sideroblastic anaemia (a type of anaemia caused by impaired haemoglobin synthesis)
• Monitor patients taking medications that deplete B6 (isoniazid, hydralazine, penicillamine)
• Evaluate patients taking high-dose B6 supplements for possible toxicity

Normal Ranges

PLP is the preferred measurement as it reflects tissue stores. Reference ranges may vary between laboratories.

Causes of Low Vitamin B6

• Poor dietary intake: B6 is found in a wide range of foods, but deficiency can occur with very restrictive diets
• Medications: Isoniazid (TB treatment), hydralazine, penicillamine, oral contraceptives, and some anticonvulsants
• Alcohol use: Alcohol promotes B6 degradation and increases urinary excretion
• Malabsorption: Coeliac disease, Crohn's disease, and ulcerative colitis
• Kidney disease: Dialysis removes water-soluble vitamins including B6
• Autoimmune conditions: Rheumatoid arthritis and other inflammatory conditions deplete B6
• Pregnancy: Increased demand, particularly in the third trimester
• Ageing: Plasma PLP levels tend to decline with age

Causes of High Vitamin B6

• Excessive supplementation: The most common cause — doses above 100mg/day over months can cause toxicity
• B6 toxicity (pyridoxine neuropathy): Chronic high-dose supplementation can paradoxically cause the same peripheral neuropathy it prevents when deficient

Important: The UK recommended upper limit is 200mg/day from supplements, but the European Food Safety Authority advises no more than 25mg/day. Toxicity has been reported at doses as low as 50mg/day taken chronically.

How to Maintain Healthy B6 Levels

• Eat B6-rich foods: Poultry, fish, potatoes, chickpeas, bananas, and fortified cereals
• Don't over-supplement: A standard multivitamin (1.4–2mg B6) is sufficient for most people
• Avoid megadoses: Do not exceed 10mg/day from supplements unless under medical supervision
• Support homocysteine metabolism: Combine B6 with adequate folate and B12 for cardiovascular protection
• Monitor if on depleting medications: Patients on isoniazid are routinely prescribed pyridoxine supplementation

When Should You Get Tested?

• You experience peripheral neuropathy (tingling, numbness, burning sensations in hands or feet)
• You have elevated homocysteine levels
• You take medications known to deplete B6
• You are taking high-dose B6 supplements and want to check levels
• You have persistent dermatitis, mouth ulcers, or a sore tongue
• You follow a very restrictive diet

Which Lola Health Tests Include Vitamin B6?

• Peak Insights — our most comprehensive panel including B6 and 70+ biomarkers