A 2017 study examined the effect of flavanones – commonly found in citrus fruits – on vessel function in the fed state. The study found that orange-derived flavanones rescue eating-induced decreases in blood vessel function.
The temporary reduction in blood vessel function that occurs after eating, and with high-fat meals, in particular, is thought to increase the risk of vessel complications and cardiovascular disease. Evidence suggests flavanones – commonly found in citrus fruits – improve vessel function and cardiovascular risk, potentially through the action of nitric oxide and related compounds which improve dilation (the widening of vessels), increasing blood flow. Most research on flavanones has been conducted during the fasted state, and as such, research into these effects during the fed state are needed to complement these findings.
In a 2017 UK study published in the British Journal of Nutrition, researchers sought to determine the effect of orange-derived flavanones on vessel function in the fed state. Fifty-nine non-smoking, male volunteers aged 30-65 were recruited for the study. All participants had to have between 0.8 and 3.2 mmol/L of fat and 6.0-8.0 mmol/L cholesterol in the bloodstream, and a body mass index between 25 and 32 kg/m2. In addition, patients could not be on supplements or fish oils, engage in a weight loss regimen, and had to be able to consume the meals provided.
Participants were instructed not to consume alcohol or foods and beverages high in polyphenols (of which flavanones are a type) or nitrates (which the body can convert to nitrites and nitric oxide), and not to engage in rigorous exercise before and during the study period, except on visit dates. Participants also ate nothing for the 12 hours prior to each visit, consuming only the nitrate-rich water supplied them. Each subject visited the Hugh Sinclair Unit 4 times during the study at 2-week intervals. During each visit, each subject consumed his prescribed beverage – a flavanone-free (control) drink, orange juice (OJ; 129 mg flavanone), flavanone-rich orange juice (FROJ; 272 mg flavanone), or a whole orange beverage (WO; 453 mg flavanone) – accompanied by a high-fat breakfast. A medium-fat lunch at 5.5 hours and normal-polyphenol dinner were provided later in the day. Blood samples – used to assess levels of nitrates, nitrites, nitric acid-containing compounds, and certain by-products of the flavanones hesperetin and naringenin – were collected 30 minutes after arrival at the Unit in the first visit (referred to as baseline), directly after each beverage consumption, and 2, 5, 7, and 24 hours thereafter. Systolic and diastolic blood pressures, assessed using a pressure monitor on the upper arm, and dilation of the brachial artery, assessed using ultrasound, were also measured directly after beverage consumption, and after 2, 5, 7, and 24 hours.
Brachial artery dilation decreased after 2 hours for all subjects, though after 5 hours dilation increased to baseline levels for non-control subjects. Significant changes in brachial artery dilation were observed at 7 hours after beverage consumption (after the medium-fat lunch) for all non-control groups, with FROJ subjects experiencing the greatest increases in dilation, followed by OJ, and then WO subjects. Significant increases in hesperetin by-products were observed at 5 and 7 hours, while significant increases in naringenin by-products were observed at 2, 5, and 7 hours. Blood naringenin levels were higher for WO and FROJ subjects than for OJ subjects at 2, 5, and 7 hours. Blood hesperetin levels were higher in FROJ subjects than in WO or OJ subjects at 5 and 7 hours. Overall blood flavanone levels did not differ between FROJ and WO groups. At 24 hours flavanone levels for all four groups returned to baseline levels. In the analysis, hesperetin levels were the strongest predictor of changes in brachial artery dilation between 0 and 7 hours, and were especially useful in predicting the size of the maximal change in dilation, observed at 7 hours. Levels of nitrates decreased at 2, 5, and 7 hours for all groups, though in the OJ, FROJ, and WO groups nitrite levels did not change significantly from baseline levels. Blood pressure remained consistent throughout.
The study findings suggest orange-derived flavanones rescue eating-induced decreases in vessel function. The peak increases in dilation, occurring at 7 hours, coincided with high levels of flavanone by-products, and nitrite levels remained consistent for all but the control subjects, and as such these findings also suggest flavanones may lead to increased vessel dilation by improving the availability of nitrites to the cells of the vessel wall. Blood levels of flavanones and coinciding changes in dilation did not differ significantly between the FROJ and WO groups, despite differences in flavanone levels in the beverages, suggesting a plateau in the absorption and effects of flavanones at these levels. As not all by-products of hesperetin and naringenin were accounted for in this study, future study would benefit from examining the effect of these other by-products on vessel function in order better understand the mechanisms at play.
Written By: Raishard Haynes, MBS