Flavan-3-ols, a class of polyphenolic compounds found in foods like tea, cocoa, apples, and grapes, have been studied for their effects on vascular health, including support of capillaries and microcirculation. Scientific evidence suggests that flavan-3-ols can improve endothelial function, modulate capillary permeability, and enhance microvascular blood flow. Several randomized controlled trials and meta-analyses have shown that consumption of flavan-3-ol-rich foods or extracts (such as cocoa flavanols) is associated with improved vascular function, reduced blood pressure, and enhanced capillary responsiveness. For example, studies indicate that regular intake of cocoa flavanols increases nitric oxide bioavailability, leading to vasodilation and improved microcirculation. These effects are relevant to capillary health, as they can improve nutrient and oxygen delivery at the microvascular level.

However, while the evidence supporting general vascular benefits is fairly strong, direct evidence specifically targeting capillary structure and function in humans is more limited. Most studies focus on broader cardiovascular endpoints or endothelial function rather than isolated capillary effects. Thus, while there is scientific validation for the use of flavan-3-ols in supporting vascular and microvascular health, the evidence specifically for capillary support is moderate (rated 3/5), with more research needed to clarify specific mechanisms and clinical benefits for capillaries.