Flavonoid-rich fruits and vegetables improve vascular function in men at risk of cardiovascular disease – FLAVURS: a randomized controlled trial
The health benefits of fruits and vegetables (F&V) are widely promoted, with higher F&V consumption commonly suggested as an effective therapy in the prevention of cardiovascular diseases (CVD)1. Known cardio-protective components of F&V include fibre, folate, nitrate, vitamins and phytonutrients such as fl avonoids. Flavonoids in particular are believed to benefi t vascular function by reducing progression to atherosclerosis2. Flavonoid groups such as anthocyanins, flavonols and flavanones are found in high concentrations in a variety of fruits and vegetables, especially berries, citrus fruits, apples, grapes, peppers, onions, broccoli and herbs3, and may in part be responsible for the observed cardiovascular benefi ts of F&V consumption.
Findings from epidemiological studies suggest that lower CVD risk is associated with higher F&V and flavonoid intakes1. While limited, intervention studies suggest that consumption of F&V rich in flavonoids may improve CVD risk markers, including endothelial dysfunction, inflammation and oxidative stress4-8. However, little is known about the extent to which flavonoids from F&V contribute to cardiovascular health and the corresponding optimal amounts of F&V required. At present, public health guidelines vary considerably between countries in relation to recommended quantity and type of F&V9. To address this question, an examination was conducted of the FLAvonoids and Vascular University of Reading Study (FLAVURS) to explore the optimal quantity and type of F&V required to promote vascular health and to reduce other established CVD risk markers.
The FLAVURS Trial
The study recruited 174 free-living men and women who were low consumers of F&V (e.g. eating less than the United Kingdom average of 4.4 F&V portions per day), aged 26 to 70 years, and who were identified as being at risk of CVD10. Participants were randomly assigned to one of two dietary treatment groups (high or low-flavonoid F&V), or the control group, who were asked to maintain their habitual F&V intake throughout the 18-week study. The 18 weeks were divided into three phases, consisting of six weeks per phase. Participants in the treatment groups were asked to increase their habitual daily F&V intake by +2 (phase 1), then +4 (phase 2), then +6 additional F&V portions a day (phase 3). Weekly supplies of commonly available high or low flavonoid F&V were delivered to participants. To assess treatment progress and compliance, vascular, blood, urine, anthropometric, dietary and lifestyle assessment measures were taken at baseline, 6, 12 and 18 weeks from all participants. Participants in both F&V treatment groups broadly achieved the target amounts of F&V at all phases of the study with 154 participants completing the study11.
For men consuming an additional two portions of high fl avonoid F&V per day (≥6 portions total F&Vs), improvements in endothelial-dependent microvascular reactivity, a key marker of vascular function (p=0.017) was observed, with concomitant improvements in their inflammatory markers, (reduced C-reactive protein (p=0.001), E-Selectin (p=0.0005) and vascular cell adhesion molecule (p=0.0468)).
We also found improvements in plasma nitric oxide for both men and women (p=0.0243) consuming an additional three portions of high flavonoid F&V (≥7 portions in total), which was not seen for controls or for those consuming equivalent amounts of low fl avonoid F&V. This suggested more general benefi ts to endothelial and vascular function from high flavonoid F&V compared to low flavonoid F&V and low F&V diets in general. Finally, we noted that an increase in F&V consumption, irrespective of flavonoid content in the groups as a whole, appeared to counteract the decline in vascular function observed in the control group during the course of the study, namely increased vascular stiffness, as measured by Pulse Wave Analysis (P=0.0065), and reduced plasma nitric oxide levels (P=0.0299).
Overall, increased F&V consumption conferred benefi ts to vascular function in both men and women at risk of CVD who consume less than the daily recommended amounts of F&V. In addition, high flavonoid F&V appeared to be particularly beneficial to the men in this sample. The greatest overall benefi ts were seen for both men and women when consuming three portions of high flavonoid F&V in addition to their usual daily intake.
How does this translate to public health nutrition guidance?
Our findings support recommendations to increase F&V intake to approximately six portions a day, with additional benefits from F&V rich in fl avonoids. In FLAVURS this was found to be particularly relevant for men with an increased risk of CVD.
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- Chong, M.F., et al., Impact of the quantity and fl avonoid content of fruits and vegetables on markers of intake in adults with an increased risk of cardiovascular disease: the FLAVURS trial. European Journal of Nutrition, 2013. 52: p. 361-378.