Tannins make up as much as 10% of blueberry leaves. The astringent nature of tannins likely accounts for the usefulness of blueberry leaf in treating diarrhea.¹ The astringent effect may also be soothing for sore throats.²Bilberry, blueberry’s European cousin, is used primarily for maintaining blood vessels, particularly those in the eyes. Some preliminary evidence indicates that anthocyanosides, the bioflavonoid complex common to bilberrry and blueberry may help people with diabetes, particularly if they have damage to the retina (retinopathy). However, these studies are primarily based on a standardized extract from bilberry fruit.³