Folate catabolites in spot urine as non-invasive biomarkers of folate status during habitual intake and folic acid supplementation.

Folate status, as reflected by red blood cell (RCF) and plasma
folates (PF), is related to health and disease risk. Folate
degradation products para-aminobenzoylglutamate (pABG) and
para-acetamidobenzoylglutamate (apABG) in 24 hour urine have
recently been shown to correlate with blood folate. Since blood
sampling and collection of 24 hour urine are cumbersome, we
investigated whether the determination of urinary folate
catabolites in fasted spot urine is a suitable non-invasive
biomarker for folate status in subjects before and during folic
acid supplementation. Immediate effects of oral folic acid bolus
intake on urinary folate catabolites were assessed in a short-term
pre-study. In the main study we included 53 healthy men. Of these,
29 were selected for a 12 week folic acid supplementation (400 µg).
Blood, 24 hour and spot urine were collected at baseline and after
6 and 12 weeks and PF, RCF, urinary apABG and pABG were determined.
Intake of a 400 µg folic acid bolus resulted in immediate increase
of urinary catabolites. In the main study pABG and apABG
concentrations in spot urine correlated well with their excretion
in 24 hour urine. In healthy men consuming habitual diet, pABG
showed closer correlation with PF (rs = 0.676) and RCF (rs = 0.649)
than apABG (rs = 0.264, ns and 0.543). Supplementation led to
significantly increased folate in plasma and red cells as well as
elevated urinary folate catabolites, while only pABG correlated
significantly with PF (rs = 0.574) after 12 weeks. Quantification
of folate catabolites in fasted spot urine seems suitable as a
non-invasive alternative to blood or 24 hour urine analysis for
evaluation of folate status in populations consuming habitual diet.
In non-steady-state conditions (folic acid supplementation)
correlations between folate marker (RCF, PF, urinary catabolites)
decrease due to differing kinetics.