Bioavailability of Citrus Flavanones and Their Effect on Cardiovascular Health Biomarkers

Consumption of flavanones has been associated with a reduction in risk of developing CVD, however flavanone bioavailability varies greatly in the population. The thesis aim was to investigate variations in absorption, as assessed by urinary excretion and, for the first time, the effect of commercially-available citrus supplements on CVD risk biomarkers. In study 1, 15 participants consumed orange juice (OJ; 500 ml: 8 mg naringenin, 42 mg hesperidin/100 ml) and/or soya-nuts (25g): 30 mg daidzein, 57 mg genistein/100 g). Urine was collected at 0, 0-4, 4-8, 8-12, 12-24 and 24-36 hr on each of three separate occasions; saliva was collected hourly (0-8 and 24 hr) after co-ingestion of OJ and soya-nuts. Daidzein was excreted to a greater extent than genistein (27-28% of dose ingested compared to 16-19%), whilst naringenin was excreted to a greater extent than hesperetin (9% vs 2.5-3%). There was a strong positive correlation between excretion of daidzein and genistein (r=0.72, p<0.01), and for hesperetin and naringenin (r=0.72, p< 0.01). Moreover, the amount of naringenin, and daidzein or genistein were correlated when co-ingested (r=0.73, p<0.01; r=0.49, p=0.05). No flavonoid was detected in saliva at any time point. In study 2, 23 overweight participants ingested citrus supplements (114 mg hesperidin) or a placebo daily for 28 days in a randomised, cross-over intervention. Urinary excretion (24 hr) was analysed by LC-MS to determine flavanone metabolite concentration at day-1 or day-28. Hesperetin-3ʹ-O-glucuronide, hesperetin-3ʹ-O-sulfate and hesperetin-7-O-glucuronide were quantified. Supplement flavanones had similar bioavailability to OJ, and there was no cumulative increase in excretion over 28 days. There was a non-significant decrease in blood pressure and fasting blood glucose after supplementation compared to placebo, however pulse amplitude tonometry was not affected. Augmentation index was reduced after supplementation compared to baseline. Although results from this thesis showed no significant change in CVD risk biomarkers, more work should verify the protective mechanism of hesperetin metabolites at different doses on vascular health.