Astragalus has been used for centuries to help keep immune function optimal by restoring strengthening and increasing vitality (adaptogenic). It stimulates deep immunity and is best for immune deficiency where one gets sick easily or is prone to viral and bacterial infections. The active constituents include polysaccharised (glucans) saponins (astragalosides) flavonoids and phytosterols all of which contribute to the positive actions of Astragalus. One study showed Astragalus root helps promote and maintain respiratory health.