Ashitaba (Angelica keiskei) has a long history of use in traditional Japanese and Chinese herbal medicine, often consumed for its purported health benefits including longevity, vitality, and general circulatory health. While ashitaba is rich in chalcones, flavonoids, and antioxidants, its specific use for supporting the capillaries—tiny blood vessels involved in microcirculation—derives primarily from traditional beliefs rather than rigorous scientific research. Traditional practitioners have recommended ashitaba to support blood flow and vascular health, likely due to its perceived ability to promote "clean blood" and healthy circulation.

However, direct scientific studies evaluating ashitaba’s effects specifically on capillary integrity or function are limited. Some laboratory research has shown that ashitaba’s chalcones may have vasoprotective, anti-inflammatory, or antioxidant effects, which theoretically could benefit blood vessels, including capillaries. Yet, these findings are preliminary and mostly based on in vitro or animal models. No substantial clinical trials have confirmed ashitaba’s efficacy for capillary support in humans.

In summary, ashitaba’s use for capillary health is primarily justified by tradition, with minimal direct scientific validation. The evidence rating is low, reflecting the lack of strong clinical support for this specific use.