Vitamin B6 supplements and how the liver handles pyridoxine
What it found
In six healthy people, taking 100 mg of pyridoxine a day for 1 to 3 weeks raised blood levels of several B6 compounds, especially pyridoxal-P and pyridoxic acid.
Lab tests with rat liver cells showed how pyridoxine is broken down and released.
What they found
Studies in people
Main B6 form in blood
Before supplements, pyridoxal-P was the main active B6 compound in plasma, making up more than half of the total. Pyridoxal and pyridoxine were also present.
B6 levels after supplements
During pyridoxine supplementation, total plasma B6 compounds rose from 114 nM to 655 nM. Pyridoxal-P and pyridoxic acid increased 6 to 7 times, and pyridoxal increased 12 times, but pyridoxine itself did not rise.
Animal and lab studies
Liver cell processing
In lab tests with rat liver cells, radioactive pyridoxine was taken up and converted mostly to pyridoxal-P, pyridoxic acid, and pyridoxal, which were then released. The cells did not release pyridoxamine-P.
New versus old B6 pools
The newly made pyridoxal-P in liver cells did not mix freely with the pyridoxal-P already stored inside the cells. Instead, it was quickly released or broken down.
What the authors conclude
“These results suggest that orally ingested pyridoxine is rapidly metabolized in liver and its products are released into the circulation in the form of pyridoxal-P, pyridoxal, and pyridoxic acid.”
Also in their conclusions
- They conclude that pyridoxal-P is the main B6 compound in blood plasma and that both pyridoxal-P and pyridoxal are transport forms of vitamin B6.
- They suggest that pyridoxine taken by mouth is quickly broken down in the liver and its products are released into the blood as pyridoxal-P, pyridoxal, and pyridoxic acid.
- They state that the liver cannot release pyridoxamine-P into the blood.
How it was done
The authors wanted to understand how the different forms of vitamin B6 are carried in the blood and how the liver processes pyridoxine.
Six healthy adults took 100 mg of pyridoxine-HCl by mouth daily for 1 to 3 weeks, and their blood plasma was tested. The authors also incubated isolated rat liver cells with radioactive pyridoxine for 2 hours to see how it was converted.
What it can’t tell you
- The human part of this study was very small, only six people, and lasted at most 3 weeks, so it cannot show what happens over longer periods or in larger groups.
- The liver cell experiments were done in rats, so they cannot prove exactly how human liver cells behave.
- This study measured blood levels of B6 compounds, not health effects, so it cannot show whether these changes matter for health.
The paper
- Title
- Plasma content of B6 vitamers and its relationship to hepatic vitamin B6 metabolism
- Type
- Study
- Evidence
- Studies in people · animals · lab
- Summarised from
- Full text
- Cite
- Lumeng L, Lui A, Li TK (1980). Plasma content of B6 vitamers and its relationship to hepatic vitamin B6 metabolism. The Journal of clinical investigation. doi:10.1172/JCI109906Free full textPubMed 7419716DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error