Vaccinium myrtillus - Bilberry - Monograph - therapeutic uses in natural medicine

Alternative Medicine Review, Oct, 2001

Introduction

Vaccinium myrtillus (bilberry) is a member of the Ericaceae family, and is also known as European blueberry, huckleberry, whortleberry, or blueberry. It is a shrubby perennial plant one to two feet in height and can be found in the mountains and forests of Europe and the northern United States. Its branches contain alternating, elliptical, bright green leaves, and its flowers, which appear from April to June, are reddish or pink, and bell-shaped. The fruit of the bilberry plant is blue-black or purple and differs from the American blueberry in that the meat of the fruit is purple, rather than cream or white. Fruit is harvested July through September, and time of ripeness is somewhat dependent on plant elevation. Plants growing at higher elevations generally ripen later than those at lower elevations. Bilberry has been used as food for centuries due to its high nutritive value, and today represents a precious wild delicacy. Bilberry's history of medicinal use dates back to the Middle Ages, but it did not become widely known to herbalists until the 16th century when its use was documented for treating bladder stones, biliary disorders, scurvy, coughs, and lung tuberculosis. More recently, bilberry fruit extracts have been used for the treatment of diarrhea, dysentery, and mouth and throat inflammations. Bilberry leaf decoctions have been used to lower blood sugar in diabetes. (1) Currently, bilberry research is focused on the treatment of ocular disorders, vascular disorders, and diabetes mellitus.

Active Constituents

Several active constituents have been isolated from the berries and leaves of the bilberry plant, including anthocyanoside flavonoids (anthocyanins), vitamins, sugars, and pectins, which are found in the berries, and quercetin, catechins, tannins, iridoids, and acids, which are found in the leaves. (2,3) The anthocyanosides are considered the most important of the pharmacologically active components. Anthocyanoside concentration in the fresh fruit is approximately 0.1 to 0.25 percent, while concentrated bilberry extracts are usually standardized to 25-percent anthocyanosides. (3) The berry's anthocyanoside content increases as the fruit ripens, while the reverse is true of its leaf constituents. (4)

Pharmacology

Although bilberry constituents have multiple pharmacological actions, most of the research has focused on the anthocyanosides. Extracts containing anthocyanosides have been shown to possess strong antioxidant properties, (5) stabilize collagen fibers and promote collagen biosynthesis, (6-8) decrease capillary permeability and fragility, (9) and inhibit platelet aggregation. (10) Anthocyanosides and other bilberry leaf constituents prevent the release and synthesis of pro-inflammatory compounds such as histamine, prostaglandins, and leukotrienes. (6-8,11) In addition, bilberry leaf decoctions administered orally have been shown to lower blood glucose levels. (12)

Clinical Applications

Ophthalmologic Disorders

The mechanisms of action behind bilberry's beneficial effect on the eye are not completely understood. They include the ability to improve oxygen and blood delivery to the eye and to scavenge free radicals that can disrupt collagen structures and contribute to conditions such as cataracts and macular degeneration. In addition, the anthocyanosides have an affinity for the pigmented epithelium (visual purple) area of the retina, the portion of the retina responsible for vision and adjustments to light and dark. (13,14)

Vision Improvement

Bilberry extract's visual enhancement properties were first studied by French researchers on Royal Air Force pilots during World War II. Administration of bilberry extract resulted in improved nighttime visual acuity, faster adjustment to darkness, and faster restoration of visual acuity after exposure to glare. (15,16) Later studies confirmed this effect, (17,18) although a subsequent double-blind, placebo-controlled, crossover study conducted on U.S. Navy SEAL personnel did not. Fifteen male subjects given 160 mg bilberry extract (standardized to 25-percent anthocyanosides) three times daily for three weeks, showed no significant improvement in either night visual acuity or night contrast sensitivity compared to placebo. (19) Conversely, studies of bilberry extract on individuals with retinitis pigmentosa and hemeralopia (inability to see distinctly in bright light) demonstrated a significant improvement in visual performance. (18,20) It may be the most significant effects will be observed in those with impaired visual acuity.

Glaucoma

Consumption of bilberry extracts may offer significant protection against the development of glaucoma due to its collagen-enhancing and antioxidant properties. The reduced tensile strength and integrity of aging eye tissue may result in the increased intraocular pressure and loss of peripheral vision seen in glaucoma. In one study, eight patients with glaucoma were given a single oral dose of 200 mg Vaccinium myrtillus anthocyanosides and demonstrated improvement based on electroretinography. (13) A collagen-stabilizing effect on the trabecular meshwork, facilitating aqueous outflow, may provide a potential mechanism.