Vitamin B6, Plasma

Vitamin B6 (pyridoxal-5-phosphate, PLP) is a water-soluble vitamin essential for amino acid metabolism, neurotransmitter synthesis, and immune function. It is measured in serum to assess nutritional status and evaluate neurological or metabolic symptoms.

When elevated: Elevated serum B6 levels are uncommon from dietary sources alone but can occur with excessive supplementation or certain medications. Chronically high levels have been associated with peripheral neuropathy and neurological toxicity, particularly at doses far exceeding recommended intake. When low: Low B6 status is associated with increased cardiovascular risk, impaired immune function, and neurological symptoms including peripheral neuropathy and cognitive changes. Deficiency may also elevate homocysteine levels, a cardiovascular risk factor.

B6 supports muscle protein synthesis and recovery by facilitating amino acid metabolism, particularly important during high training volumes. Athletes with inadequate intake or malabsorption may experience delayed recovery, reduced endurance capacity, or increased injury risk, making this marker relevant for those on restrictive diets or with persistent fatigue despite adequate training.