There are different kinds of B6, but only one that can be directly used by the body: P5P. All other forms have to be converted by the liver to P5P. P5P does not cause toxicity (see below), but all other forms can cause this.
Magnesium needs B6 to work properly: http://www.terrytalksnutrition.com/weekly-articles/2012/04-27/the-life-saving-value-of-pyridoxal-5-phosphate-p5p-and-magnesium/
B6 sufficiency can be subjectively determined by the return of regular (remembered) dreaming.
From: http://thorne.com/media/alternative_medicine_review/monographs/pyridoxal_phosphate_mono_6.1.pdf. There’s lots of good information in this pdf, for instance this:
- The use of supplemental P5P has not been associated with toxicity, although the inactive form, pyridoxine, has been associated with reports of peripheral neuropathy. Later note: I read that there are cases where people suffer p5p toxicity. One writes that this can be cured by taking high amounts of B12
- It mentions drug interactions
- There have been many reports of abnormal tryptophan metabolism in women taking either oral contraceptive or menopausal hormone replacement therapy, which have been interpreted as indicating estrogen-induced vitamin B6 deficiency or depletion.
- Morning sickness
- Homocysteine levels
- Carpal tunnel
Vitamin B6, The Doctor’s Report has all you need to know about P5P.
(pyridoxine = B6)
In summary, it can be said that estrogen inhibits many pyridoxine-dependant enzymes, particularly those that help transform the amino acid tryptophan to niacin. Since these substances are very important to mental health, it’s no surprise that women are subject to estrogen-related fluctuations in mood.
Extra pyridoxine reverses this simply by helping the enzymes of the tryptophan-to-niacin pathway work better, as well as other pyrodoxine-related enzymes, despite estrogen’s inhibiting influence.
This would also explain why magnesium works far less with high estrogen: the B6 that is necessary for magnesium doing its job is impeded by the estrogen.