Flavonoids, a diverse group of plant-based polyphenolic compounds, are scientifically recognized for their potential role in supporting vascular health, including capillary strength. Evidence for their use in capillary weakness stems from both in vitro and clinical studies. Flavonoids such as diosmin, hesperidin, and rutin are found in citrus fruits and other plants and have been shown to exert vascular protective effects. Their mechanisms of action include strengthening capillary walls, reducing capillary permeability, and exerting antioxidant and anti-inflammatory effects.

Several randomized controlled trials and meta-analyses have reported that flavonoid mixtures, particularly micronized purified flavonoid fraction (MPFF, commonly containing diosmin and hesperidin), are effective in reducing symptoms associated with chronic venous insufficiency, such as leg swelling and capillary fragility. These compounds appear to improve microcirculation and reduce edema, which are directly relevant to capillary weakness. Furthermore, the European Medicines Agency (EMA) and other regulatory bodies recognize certain flavonoids as traditional herbal medicinal products for the relief of symptoms related to minor venous circulatory disturbances.

However, while the evidence is moderate and supports their use, methodological differences and the heterogeneity of flavonoid preparations make it difficult to assign a higher evidence score. More robust, high-quality clinical trials are needed to fully establish their efficacy and optimal dosing for capillary weakness specifically.