The vitamin B6 paradox: Supplementation with high concentrations of pyridoxine leads to decreased vitamin B6 function.
Level 5 - mechanism / opinion, no new human data
In vitro cell line and enzyme assay study (bench research)
PubMed 28716455 · doi:10.1016/j.tiv.2017.07.009
What was done
Human neuroblastoma (SHSY5Y) and intestinal epithelial (CaCo-2) cells were exposed for 24 hours to five distinct vitamin B6 vitamers: pyridoxine, pyridoxamine, pyridoxal, pyridoxal-5-phosphate, or pyridoxamine-5-phosphate. Following exposure, cell viability was measured using the MTT assay, and expression of apoptotic markers Bax and caspase-8 was quantified. The effects of the vitamers on the activity of two pyridoxal-5-phosphate-dependent enzymes were also evaluated.
What was found
The abstract reports no exact numerical values, concentrations, or effect sizes. It states that pyridoxine induced concentration-dependent cell death in SHSY5Y cells, whereas the other vitamers did not affect cell viability. Pyridoxine significantly increased Bax and caspase-8 expression and inhibited both pyridoxal-5-phosphate-dependent enzymes.
Why it matters
This study proposes a mechanistic basis for peripheral neuropathy caused by high-dose vitamin B6 supplementation, suggesting that inactive pyridoxine competitively inhibits the active coenzyme pyridoxal-5'-phosphate to cause functional B6 deficiency.
Limits
All experiments were conducted in vitro using immortalized cell lines (SHSY5Y and CaCo-2) and isolated enzyme assays, which cannot replicate human pharmacokinetics, metabolism, or blood-nerve barrier dynamics. The abstract does not report specific vitamer concentrations, effect magnitudes, or statistical parameters.
Cited by
- partial Inactive forms of vitamin B6 and folic acid accumulate toxically if not supplied in their active state to individuals with genetic methylation issues.