Vitamin B6 is found in plant and animal sources. Plants contain mostly pyridoxine and animals contain mostly pyridoxal. These two forms need to be converted to its active form, pyridoxal 5 phosphate (PLP), by the enzyme, pyridoxal kinase, for it to perform its many important functions. The recommended intake for B6 is 1.7mg daily. However in most people, the enzyme pyridoxal kinase, isn’t functioning properly, and the conversion of B6 to its active form is 1:5-10 and sometimes close to zero. As seen here, there was only a 33% increase in PLP, with those who have liver damage. Plus urinary excretion of pyridoxic acid increased significantly. The less conversion you are able to do, the more wasting takes place. (R) The enzyme also requires vitamin B2 as a cofactor. So one can actually have a B6 (PLP) deficiency, even while eating enough B6 through foods. To skip all these issues, you can just supplement with PLP from the start. More on supplements at the bottom.
Skeletal muscle contains about 80% of stored B6 and is involved in the metabolism of some amino acids (citrulline, arginine, lysine and threonine) (11, 12)
It’s involved in the conversion of ornithine to proline and a defect of this PLP enzyme can lead to blindness.
B6 supplementation significantly increases carnosine and/or calcium regulator (13, 14)) in muscle as well as beta-alanine (which is the precursor to carnosine) (15).
Carnosine stimulates mitochondrial biogenesis and is an integral part of skeletal muscle contractility and homeostasis, presumably through its role as anti-oxidant, pH-buffering (inhibit lactate formation), anti-glycation (reducing the rate of formation of advanced glycation end-products (AGEs), which are substances that can be a factor in the development or worsening of many degenerative diseases, such as diabetes, atherosclerosis, chronic renal failure, and Alzheimer’s disease)).
B6 also increases many gene expressions and polyamines that are involved in muscle growth and repair. (R)
Vitamin B6 also lowers the cortisol receptor responsiveness, which can help with building muscle (R). Only pyridoxal 5 phosphate appear to have this effect.
A vitamin B6 deficiency can also lead to low thyroid hormone production. Thyroid hormone are essential for building muscle and staying lean. Read more on thyroid and muscle growth here.
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