Rye bran bread intake elevates urinary excretion of ferulic acid in humans, but does not affect the susceptibility of LDL to oxidation ex vivo

Background Rye bread contributes an important part of the whole grain intake in the Scandinavian diet. Ferulic acid is the major phenolic compound in rye bran and is an antioxidant in vitro and may, therefore, contribute to cardioprotective effects of whole grain consumption. Aim of study Firstly, to evaluate the bioavailability and potential antioxidative effects in humans of ferulic acid from rye. Secondly, to evaluate urine levels of ferulic acid as a possible biomarker of the ordinary dietary intake of ferulic acid. Methods We determined the urinary excretion of ferulic acid in 18 postmenopausal women after a dietary intake of rye bran or an inert wheat bran (control) in a crossover study (2 x 6 weeks with 4 weeks washout). The potential antioxidative effect of the rye bran intervention was investigated by measuring low-density lipoprotein (LDL) susceptibility to copper oxidation ex vivo. The subjects ingested rye bran enriched breads equivalent to similar to 10.2 mg ferulic acid per day. Results The urinary excretion of ferulic acid averaged similar to 4.8 mg per day during intervention with rye bran breads and similar to 1.9 mg per day on the control breads (P = 0.002). Rye bran intervention had no influence on lag time or propagation rate of the LDL oxidation ex vivo. Conclusions The present study demonstrated that ferulic acid from rye bran is bioavailable and that the urinary concentration of ferulic acid reflects the dietary intake of this hydroxycinnamic acid. Within the period of intervention, the elevated ferulic acid did not produce a measurable antioxidative effect on the subjects' LDL. It is suggested that the determination of ferulic acid in urine is a useful biomarker to assess the intake of ferulic acid from a regular diet.