Am J Clin Nutr. 1998 Feb; 67(2): 221-30.

Urinary, plasma, and erythrocyte carnitine concentrations during transition to a lactoovovegetarian diet with vitamin B-6 depletion and repletion in young adult women.

Chen W, Huang YC, Shultz TD, Mitchell ME.

Department of Food Science and Human Nutrition, Washington State University, Pullman 99164-6376, USA.

The purpose of the present study was to determine whether vitamin B-6 depletion and repletion influence carnitine concentrations in the plasma, erythrocytes, and urine of young adult women consuming a low-carnitine (30 micromol/d), lactoovovegetarian diet. Doses of vitamin B-6 were administered sequentially as follows: 1.60 mg/d during adjustment for 9 d, 0.46 mg/d during depletion for 27 d, 1.26 mg/d during the first repletion for 21 d, 1.66 mg/d during the second repletion for 21 d, and 2.06 mg/d during the third repletion for 14 d. Urinary carnitine tended to decline but was not significantly different throughout the 92-d study period. Plasma short-chain acylcarnitine and total carnitine decreased during vitamin B-6 depletion; however, the ratio of plasma acylcarnitine to total carnitine was not significantly different during changes in vitamin B-6 intake. Erythrocyte long-chain acylcarnitine increased during vitamin B-6 depletion, but the ratio of erythrocyte acylcarnitine to total carnitine did not respond to changes in vitamin B-6 intake. Plasma free and total carnitine concentrations were only weakly correlated with plasma pyridoxal-P concentration (r = 0.28 and r = 0.29, respectively; P < 0.01). No significant correlations were observed between urinary carnitine excretion or erythrocyte carnitine concentrations and plasma or erythrocyte pyridoxal-P concentrations. Thus, a vitamin B-6 intake of 0.5 mg/d does not affect carnitine concentrations in biological fluids and therefore is unlikely to affect endogenous carnitine synthesis over 27 d. The changes in carnitine indexes that we observed were probably due to adaptation to a vegetarian pattern of exogenous carnitine consumption.