URINARY-EXCRETION OF [H-2(4)]FOLATE BY NONPREGNANT WOMEN FOLLOWING A SINGLE ORAL DOSE OF [H-2(4)]FOLIC ACID IS A FUNCTIONAL INDEX OF FOLATENUTRITIONAL-STATUS

In a 10-wk study with nonpregnant women (21-27 y, n = 5-6 per group), subjects were fed a diet containing similar to 68 nmol/d (30 mu g/d) f olate from food that was supplemented with folic acid in apple juice t o yield a constant intake of 454, 680 or 907 nmol/d (200, 300 or 400 m u g/d) to evaluate folate status and long-term in vivo kinetics. Repor ted here is an additional phase of this protocol conducted to determin e the relationship between short-term urinary excretion after a single isotopically labeled dose and various measures of folate nutritional status. It was hypothesized that urinary excretion from a single [glut amate-H-2(4)]folic acid ([H-2(4)]folic acid) dose would increase in pr oportion to folate nutritional status due to saturable cellular uptake and retention processes along with saturation of renal reabsorption. Each subject was given 1.13 mu mol (500 mu g) of [H-2(4)]folic acid or ally on the morning of d 70 of the study, followed by a complete 24-h urine collection. Urine was analyzed to determine the isotopic enrichm ent of urinary folate by gas chromatography-mass spectrometry and the concentration of urinary folate by HPLC, Urinary excretion of [H-2(4)] folate was greatest at the 907 nmol/d intake and was positively correl ated with serum folate concentration but was not correlated with eryth rocyte folate. Excretion of [H-2(4)]folate tended to be greatest when plasma homocysteine concentrations were low (<8 mu mol/L), although th is relation was not significant. These results suggest that 24-h urina ry excretion after a single oral dose of isotopically labeled folate i s a functional indicator of folate nutritional status that complements other measures of folate nutriture.