Bilberry extract for night vision.
* Trials have shown mixed results for efficacy, but a systematic review has recommended further study.
History of Use
Legend has it that during World War II, British Royal Air Force pilots noticed that the accuracy of their nightly bombing runs over Germany improved markedly if they ate bilberry jam beforehand. The story may be apocryphal, but it has been perpetuated the interest in bilberry extracts for visual acuity.
Bilberries have a long history of medicinal use. In his 1633 edition of his "The Herball," John Gerard noted that apothecaries boiled the berries with sugar and honey, and offered the resulting mixture, called rob, as a remedy that "be good for an hot stomacke."
In Mrs. M. Grieve's 1931 "Modern Herbal," she reported that syrup made from bilberries is "especially valuable in diarrhea and dysentery" and further noted "a decoction of the leaves or bark of the root may be used as a local application to ulcers," and observed that a related fruit, the farkleberry, was useful for "chronic ophthalmia."
Mechanisms of Action
Berries of the Vaccinium myrtillus shrub contain high concentrations of anthocyanosides, which are flavonoid compounds found in many pigmented fruits. These antioxidant compounds, have been described as accelerating the resynthesis of rhodopsin, a chromoprotein in retinal rods that stimulates the retinal sensory endings as it is formed and degraded (Soc. Biol. Clermont-Ferrand. 160:1590-93, 1966). Anthocyanosides also were reported to modulate retinal enzyme activity (Rev. Med. Aeronaut. Spat. 18:45-50, 1966). Their antioxidant activity is said to slow retinal angiopathy that occurs in age-related macular degeneration and diabetic retinopathy.
Numerous investigations have been undertaken on the effects of anthocyanoside extracts on human vision during the past 4 decades, and a recent systematic review has addressed and analyzed the conflicting findings from these studies (Surv. Ophthalmol. 49:38-50, 2004).
The reviewers identified 30 trials testing the effects of these extracts on vision under reduced light circumstances, 12 of which met their inclusion criteria.
Of five randomized controlled trials, only one showed significant differences in ocular measurements after administration of tablets containing 100 mg of anthocyanosides extracted from V. myrtillus and 5 mg [beta]-carotene. This study of 37 subjects with normal vision showed significant improvements in dark-adaptation thresholds and significant increases in the macular field of vision under high mesopic light (Therapie 19:171-75, 1964).
The remaining four randomized trials, including one conducted at the Naval Aerospace Medical Research Laboratory, Pensacola, Fla., found no differences on measures such as scotopic retinal thresholds, mesopic contrast sensitivity, and visual acuity. In the Pensacola study, 15 Navy SEALs aged 25-47 years were given 120 mg/day of bilberry extract or placebo for 21 days, at which time no differences could be detected in night visual acuity or night contrast sensitivity (Altern. Med. Rev. 5:164-73, 2000).
Seven nonrandomized trials, most of which took place during the 1960s, all found improvements following administration of anthocyanoside extracts on at least one outcome measure, such as global retinal light threshold or scotopic light threshold. In one study of 16 patients in an ophthalmologic clinic, electroretinograms showed significantly more rapid dark adaptation in those given the active extract than in those given placebo (Minerva Oftalmol. 24:189-93, 1983).
The authors of the systematic review pointed out multiple limitations and drawbacks of the trials, including different test methods and uncertain extraction methods in the older studies, short duration of treatment, and variations in dosage or even failure to report dosages. The trials with negative outcomes used the lowest doses, "suggesting an association between positive outcome and higher dose levels."
They also said that high performance liquid chromatography analysis of extracts obtained from different parts of Europe and Scandinavia found notable variations in phytochemical composition. Two of the negative trials with low doses both used tablets formulated from Swedish bilberries. Most of the positive trials, in contrast, used Italian or French products.
The reviewers also noted that a recent double-blind study testing the effect of another anthocyanoside-containing berry, black currant, found statistically significant lowering of dark-adaptation thresholds 30 minutes after a single 50-mg dose among 12 healthy volunteers (Altern. Med. Rev. 5:553-62, 2000). Also, a synthetic cyanidin-based anthocyanoside product was tested in a number of placebo-controlled trials during the 1970s and 1980s that consistently showed positive effects on night vision in patients with a variety of ophthalmologic disorders.
Despite the limitations of the studies, the reviewers determined that there was sufficient potential for benefit to warrant further trials of anthocyanoside extracts for patients with poor night vision and other visual difficulties. They also recommended closer analysis of extracts from southern Europe and the uniform adoption of modern ophthalmologic methodology for the measurement of dark adaptation and scotopic and mesopic visual acuity.
No adverse events were reported in any of the trials. In a postmarketing surveillance study that included 2,295 subjects, 94 complained of side effects that were primarily gastrointestinal, cutaneous, or CNS-related (Fitotherapia 67:3-29, 1996).
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|Title Annotation:||Alternative medicine: an evidence-based approach|
|Publication:||Family Practice News|
|Date:||Jul 15, 2004|
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