Horse chestnut is one of the better-validated German herbal medications. Doctors throughout Europe prescribe horse chestnut to treat varicose veins, chronic venous insufficiency and leg swelling.
One way that horse chestnut functions is to reduce the number and diameter of small pores in the capillary membranes, thus reducing the escape of fluid into the surrounding tissues. This "sealing" effect in the capillaries improves blood flow in the veins, and reduces swelling of small veins in the legs.
Another mechanism by which horse chestnut works indicates that it also could have antiaging effects. In addition to improving circulation, horse chestnut inhibits an enzyme called hyaluronidase that degrades hyaluronic acid, used by skin and capillary cells as part of the proteoglycan "jelly" to hold collagen fibers in place. Horse chestnut inhibits the age-related breakdown of hyaluronic acid, and by doing so stabilizes the support structures for the veins, skin and other connective tissues.