What causes low vitamin B6 levels?

Causes of Low Vitamin B6 Levels

Low vitamin B6 levels are most commonly caused by inadequate dietary intake, malabsorption issues, medication interactions (particularly isoniazid), and age-related physiological changes. 1

Primary Causes of Vitamin B6 Deficiency

• Inadequate dietary intake is a major cause of vitamin B6 deficiency, particularly in elderly populations who may have reduced consumption of vitamin B6-rich foods such as lean meat, milk, dairy foods, and fortified cereals 1
• Age-related decline in vitamin B6 intake is consistently observed in studies with extended follow-up periods, with significant age-related decline in intake (P < 0.001) 2
• Medication interactions can significantly affect vitamin B6 metabolism, with several medications acting as vitamin B6 antagonists 3, 1:
  • Isoniazid (tuberculosis drug) competes with pyridoxal phosphate for the enzyme apotryptophanase 4
  • Penicillamine can inhibit vitamin B6 activity 3
  • Anti-cancer drugs can interfere with vitamin B6 metabolism 3
  • Corticosteroids can inhibit vitamin B6 activity 3
  • Anticonvulsants can alter vitamin B6 metabolism 3
• Malabsorption conditions contribute to deficiencies of multiple B vitamins, including B6 1

Prevalence and Risk Factors

• Vitamin B6 deficiency (plasma PLP < 30 nmol/l) has been reported to affect 49% of community-dwelling and 75% of institutionalized elderly (>65 years) in the UK 2
• In the US, pyridoxine deficiency was suggested to have reached epidemic proportions, affecting 71% of men and 90% of women 2
• Institutionalized elderly show higher prevalence of inadequate intake, with more than 50% of residents in long-term care facilities having inadequate vitamin B6 intake 2
• Chronic kidney disease patients are at particular risk due to altered vitamin B6 metabolism and increased clearance with certain medications like furosemide 5

Biochemical vs. Dietary Assessment

• Biochemical data often reveals a more concerning picture than dietary intake assessments 2
• Studies have identified biochemical deficiency (using PLP values) in up to 49% of elderly populations with supposedly "adequate" mean intake 2
• The prevalence of pyridoxine deficiency according to biochemical indices typically ranges between 26-59% in free-living and 5.3-49% in non-free-living elderly populations 2

Clinical Implications

• Low vitamin B6 status is associated with increased risk of:
  • Hip fractures in women (22% increased risk in those with lowest quartile of intake) 2
  • Fragility fractures (women in highest quartile of intake have significantly reduced risk, HR = 0.55) 2
  • Hyperhomocysteinemia, which is linked to cognitive impairment and dementia 6
  • Neuropsychiatric disorders including seizures, migraine, chronic pain, and depression 6
  • Cardiovascular disease, cognitive dysfunction, osteoporosis, anxiety 7

Monitoring and Management

• For patients with confirmed vitamin B6 deficiency receiving supplementation, blood levels should be checked at first assessment and repeated within 3 months after supplementation 3
• PLP-based supplements are preferred over pyridoxine supplements due to minimal neurotoxicity 8
• Weekly administration of vitamin B6 supplements (50-100 mg) is preferred over daily use to prevent toxicity, aiming for stable serum PLP levels between 30-60 nmol/L 8
• For hemodialysis patients without erythropoietin (EPO) treatment, 5 mg/day of pyridoxine is recommended; for those with EPO treatment, 20 mg/day is recommended 5