Plasma folate but not vitamin B(12) or homocysteine concentrations are reduced after short-term vitamin B(6) supplementation.

Adverse effects of high vitamin B(6) intake include peripheral neuropathy. Recent studies focussing on the reduction of plasma homocysteine as a risk factor for vascular disease showed that vitamin B(6) reduces plasma folate levels. The significance of this finding is unclear. We therefore analyzed plasma folate and basal homocysteine levels as well as the response to an oral methionine loading test in 8 healthy individuals before and after a controlled supplementation with oral doses of 25 mg pyridoxine for 10 days. Plasma pyridoxal phosphate increased from 40.6 +/- 13.6 to 426.8 +/- 200.3 nmol/l (p < 0.001), whereas plasma folate decreased from 6.3 +/- 1.6 to 4.6 +/-1.5 ng/ml (p < 0.01), respectively. Plasma vitamin B(12) and basal homocysteine levels remained unchanged (234.0 +/- 27.8 vs. 217.1 +/- 50.4 pg/ml and 10.9 +/- 4.8 vs. 10.1 +/- 3.6 micromol/l). There was no significant effect of vitamin B(6) supplementation on the area under methionine and homocysteine concentration versus time curve. Significant correlations were found between pre- and post-supplement levels of folate as well as PLP levels (r = 0.73, p < 0.05; r = 0.75, p < 0.05). These data suggest that a dose of 25 mg vitamin B(6) supplemented for 10 days reduces plasma folate but did not affect basal and postprandial homocysteine levels suggesting (1) a normal cellular availability of folate or (2) a compensation of impaired homocysteine remethylation by increased transsulfuration. Copyright 2001 S. Karger AG, Basel