Total body phylloquinone and its turnover in human subjects at two levels of vitamin K intake

Abstract

The aims of this study were to determine the total body phylloquinone and its metabolic turnover in human subjects using a tracer dose of [5-H3]phylloquinone containing 55·5×104MBq/mmol. Seven subjects aged 22 to 49 years were given 0·3 μg isotopic phylloquinone intravenously on a control diet (75 μg phylloquinone/d) and blood, urine and faeces were sampled periodically for 6 d. Five of these subjects were studied a second time after 3–8 weeks on a low-vitamin K diet (8 μg/d). The changes in the radioactivity of plasma phylloquinone with time were analysed by the method of residuals and fitted to a curve composed of two exponential components. The size of the exchangeable body pool was calculated by isotope dilution. Plasma phylloquinone levels fell during vitamin K restriction but the vitamin K-dependent coagulation factors did not change. After injection the first exponential decay curvet1/2was 1·0 (SD 0·47) H IN THE SUBJECTS ON THE CONTROL DIET AND 0·49 (sd 0·27) h after vitamin K restriction. On the control diet, the second exponentialt1/2was 27·6 (sd 124) h that did not change on the low-vitamin K diet (t1/2=25·1 (sd 13·5) h). These results indicate that the turnover time for phylloquinone in human subjects is about 1·5 d. Urinary excretion of3H-metabolites ranged from 30 % of the administered dose on the control diet to 38 % on the restricted diet and had the same turnover rate as the second component of the plasma decay curves. The exchangeable body pool of phylloquinone declined from about 1·0 μg/kg before restriction to lower values after vitamin K restriction. The faecal excretion of phylloquinone and its metabolites fell from 32 % of the administered dose on the control diet to 13 % on the restricted diet.