01-06-2009, 10:06 PM
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Bilberries - A Clinical Perspective
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Bilberries have been used for non specific diarrhea, venous insufficiency of the lower limbs, for varicose veins, hemorrhoid conditions, inflammation of the mouth, improving visual acuity and degenerative retinal conditions.3 Bilberry extract is marketed in Europe as a prescription drug for venous disorders and heavy legs.
Bilberry has been fairly well evaluated clinically relevant to its health benefits for the eyes and vision as well as for its overall vascular support.4,5 While a recent systematic review examined 30 trials regarding visual acuity, and concluded bilberry anthocyanins do not support improvement of normal night vision;6 it was noted the studies lacked rigorous clinical evaluation of the effects of bilberry on subjects with actual impaired night vision due to their poor eye health conditions. In other words, the conclusion was based on outcomes derived from healthy individuals.
Further all trials that reported negative outcomes used low daily dosing, between 12 mg/d and 60 mg/d. More positive outcomes were seen in trials with significantly higher dosing, between 300 and 720 mg/d.
Regarding retinopathy due to diabetes complications, most studies demonstrate improvements in retinal function.7,8,9 Notably, inconsistencies to the treatment persist; dosing for these studies varied appreciably, 320 to 600 mg/d, as well as the duration of treatment anywhere from 1 month to one year. Only three of these studies were placebo controlled.
The protective vascular activity of bilberry is attributed to its anthocyanin content, which exhibits specific affinity to capillary blood vessels of the eye and other vascular tissues. Anthocyanins bind with the phospholipids of the inner lining of blood vessels and increase the biosynthesis of proteoglycans, the basic constituents of the connective tissue of capillaries; and inhibit the activity of the proteolytic enzymes collagenase and elastase. Both of these effects result in capillary reinforcement and reduction of their permeability.
Such mechanisms of action, along with bilberry's antioxidant properties, reduce vascular inflammation. Further, bilberry anthocyanins induce nitrous oxide production, serving as a potent vascular dilator. Along with this vascular dilative action anthocyanins have also been clinically shown to exhibit antiplatelet aggregation.10
The combination of these mechanisms results in the following vascular benefits from bilberry:
- Improvement of blood flow in capillary blood vessels; reducing venous inflammation and treating circulatory disorders of the retina.
- Maintaining integrity of connective tissue surrounding blood vessels; treating acute attack of piles.
- Reduce edema and capillary fragility of skin and mucosa; indicative for reducing echymosis (bruising), gingival hemorrhage, epistaxis and facilitating re-absorption of fluids.
Newer trials are examining whether bilberry’s vascular health benefits can work synergistically with other nutrients that are rich in polyphenol compounds. For example, one trial looked at a combination of bilberry and pine bark extract (180mg/80mg/d) dosing, which resulted in intraocular pressure decrease thus beneficial to glaucoma sufferers.11
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Bilberries—A Clinical Perspective
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