Researchers1 have investigated the effects of flavonoids and flavonoid sub-classes on hypertension in 135,957 healthy men and women from the Nurses’ Health study (NHS) I, NHS II and Health Professional Follow-Up Study. The flavonoid quantities in the diets were calculated from food frequency questionnaires which were collected every 4 years from the study participants. The results showed that those in the highest quintile for anthocyanin intake had an 8% reduction in the risk of hypertension compared with the lowest quintile. For the flavone apigenin, the reduction in risk between the highest intake quintile and the lowest intake quintile was 5%. In participants under 60 years of age, there was a 5% and 7% reduction in hypertension risk between those in the highest intake quintile for the flavon-3-ols epicatechin and catechin respectively, compared to the lowest intake quintile.
Anthocyanins, flavan-3-ols and flavones may have beneficial effects of vascular tissue, based on their structural characteristics (figure 1). Apocynin is a drug known for its vasoactive properties based on its ability to inhibit NADPH oxidase, an enzyme that may decrease the bioactivity of the endothelium derived relaxing factor (EDRF; nitric oxide). The methylated forms of catechol flavonoids (such as catechin and epicatechin) as well as flavonoids possessing only one 4’-hydroxy group (such as apigenin and the anthocyanin pelargonidin) can also act as inhibitors of NADPH oxidase. Interestingly, the anthocyanins consumed by the study participants were mainly from strawberries and blueberries which are particularly high in pelargonidin. The ability of flavonoids to reduce hypertension in those subject under the ages of 60 may suggest that cumulative damage to the endothelium is not able to be overcome by the beneficial effects of flavonoids in inhibiting NADPH oxidase.
Figure 1. Structural characteristics of flavonoids (catechin, pelargonidin and apigenin) and the drug apocynin. Flavonoids have A, B and C rings which can be variously hydroxylated.
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