Bilberry has been recognized as a class one herb by the American Herbal Products Association which further validates the safety of consuming Bilberry. In fruit markets, Bilberry is available as fresh, frozen, and dried whole berries and is commonly used in the preparation of commercial food products like jams, and juices. Food supplementation industry prepares Bilberry powder and liquids, as it is a rich source of several phytochemicals, including anthocyanins (a potent antioxidant agent).
What is Bilberry?
The bilberry is a small fruit having a diameter around 5mm to 9 mm of bluish black in color. Multiple seeds are present in the fruit pulp. The Scientific name of Bilberry is Vaccinium myrtillus L., and it belongs to the same family (Vaccinium), as blueberry and cranberry. The plant of Bilberry is classified under shrubs. Bilberry has several regional names, such as European blueberry, blaeberry, whortleberry, and huckleberry. 
A recommended dose of Bilberry supplement for a short period of time can deliver several health benefits without giving any side effects. However, taking leaves of Bilberry in high quantity for a long duration may not be safe. 
Where it is grown and what is the optimal growing condition?
The native place of bilberry shrub is northern Europe. The growth rate of this shrub is relatively low but aggregation revolution ensures the possibility that plantation of bilberry shrubs are available at North America and Asia. It has a misconception that blueberry is alternatively known as Bilberry, as both have a similar appearance but these close resembling shrubs have different native places. The United States is a native place of true blueberry while bilberry usually grows in moorland, grazing land, and soggy coniferous forests. The favorable place of Bilberry plantation is moderately shaded areas with the moist land. 
Nutrition and active compounds of Bilberry
Bilberry is a rich source of anthocyanins even more than another type of berries, like cranberry, strawberry, elderberry, raspberry and sour cherry. Apart from this, several types of phenolic compounds like quercetin, catechins (flavonols), ellagitannins, tannins, and phenolic acids are also abundantly present in Bilberry. All these phenolic compounds have antioxidant property and also bind with iron and form chelates.
The active constituents of Bilberry i.e. anthocyanin contents and phenolic compounds depends upon several factors, like growing conditions (sunlight exposure, temperature, nitrogen and phosphorus content in soil), ripeness of the berry etc. During maturation of the Bilberry, the anthocyanin contents get accumulated and more concentrated amount are found in the skin of the fruit. The range of anthocyanin content varies between 300-700 mg per 100 grams of fresh fruit but the usual daily dietary recommendation of anthocyanins consumption is approximately 200 mg. Other nutritional components in Bilberry are vitamin C and catechin. A variety of anthocyanins are present in Bilberry and among these.
History Behind Use of Bilberry
Since medieval period, the fruits and leaves of bilberry have been recognized due to its therapeutic benefits to treat conditions like diarrhea, infections, scurvy, burns, and diabetes. Ancient history has a mention of British pilots who ate jam made of bilberries during World War II, based on their popular belief that it would improve their night vision.
Health Benefits of Bilberry
Bilberry has several health benefits, which include improvement of vision and memory power, to prevent diabetes, weight management, anti-inflammatory action, as a potent antioxidant, can decrease risk of cardiovascular diseases by lowering blood pressure, can control lipid level, regulate cellular activity, detoxify body and control mutation, which further can assist to decrease the risk of cancer, and provide anti-microbial property.  Some of the key benefits of Bilberry are discussed in bellow sections.
The references from the past history provide the theory that Bilberry is effective to promote the vision and also used to treat several eye infectious diseases. Several types of research have been conducted to evaluate the efficacy of the Bilberry in eye health improvement, which includes protecting effect against cataract, macular degeneration, retinopathy and improvement of night vision. Most of the elderly patients suffer from cataract and macular degeneration which hamper their vision, whereas diabetes is a common cause of retinopathy. Several reported results supported the positive effects of Bilberry in the case of retinal abnormalities, increased capillary resistance, slowing of progression of lens opacity and myopia, and improved dark adaptation. Therefore, the exact quantity of bilberry can give protection to elderly and diabetic patients who are prone to develop a cataract, macular degeneration, and retinopathy. All the ocular benefits of bilberry are due to the presence of anthocyanins. All the eye health benefits are assessed through human trials. The light-induced ocular cell damage can be protected by bilberry due to its antioxidant property. Anthocyanins in Bilberry can able to provide defensive effect on enzymes heme oxygenase-1 (HO)-1 and glutathione-S-transferase-pi (GST-pi) in retinal pigment epithelial cells and maintain the homeostasis of the ocular cells and promote regeneration of ocular physiology. 
There are several phytochemical analytical studies that shown anthocyanins has potent antioxidant property and able to form chelates with metal ions. The anthocyanins obtained from bilberry has been found to have cell protective effect against oxidative damage, as it has a scavenger of free radicals. Anthocyanins obtain from bilberry is effective to combat against apolipoprotein B and prevent enhancement of 'bad cholesterol' level. It also acts against ultraviolet (UV)-induced oxidative fragmentation. An animal study shows that bilberry supplementation provides adequate anthocyanins, which can delay the aging by reducing oxidative stress. In addition, anthocyanins in bilberry can also reduce the toxicity of some medication like doxorubicin.
Acute Inflammation is considered as a defensive mechanism of the body, but in a chronic condition, inflammatory diseases increase oxidative stress and promote multiple ailments including cardiovascular diseases and cancer. Several study findings recommend that anthocyanins present in bilberry are effective to treat the inflammatory condition, as anthocyanins can control cellular proteins degradation through inhibiting proteasome activity. In addition, anthocyanins can inhibit nuclear factor κB activation, which stimulates inflammation by modulating genetic expression. A human study showed bilberry juice intake can control different pro-inflammatory factor and effective as immune-modulator. 
Both bilberry fruits and leaves have anti-diabetic activity. In folk medicine, bilberry used to treat diabetes from centuries. According to one of the Italian herbal survey report, bilberry gets the fourth position in anti-diabetic activity. The pathophysiology of Type 2 diabetes involves insulin resistance and pancreatic beta cell inactivity. Bilberry is effective to compensate both the pathophysiology due to its hypoglycemic effect. The animal study researchers found that anthocyanins present in bilberry can stimulate insulin secretion. In addition, the risk factors like increased oxidative stress, inflammatory condition and dyslipidemia of diabetes can also be controlled by Bilberry and provide the preventive effect. The different diabetic complications including increased risk of CVD, retinopathy can also be prevented and treated by Bilberry. 
Immune system health
The anti-inflammatory and antioxidant property of Bilberry can promote immune system and boost immune power, and immunomodulatory effect can act as anti-tumorigenic, which decrease the risk of cancer. In addition, the antimicrobial property of Bilberry prevents infections and declines related immune system.Thus, it can also prevent infection-induced aging process and chronic disorders.
Bilberry has immense health benefits which are time to time back by research evidence as discussed in this article which can further provide sufficient support to include it in our diet. All the essential phytonutrients including anthocyanins and phenolic compounds are rich in bilberry and all these health advantageous components are readily absorbable in human physiology. It offers sufficient bioavailability and bioactivity to provide the significant result as antioxidant, anti-inflammatory, hypoglycemic, and immunity booster to make it as a promising herbal therapeutic agent.
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Wing-kwan Chu, Sabrina C. M. Cheung, Roxanna A. W. Lau, and Iris F. F. Benzie.; Chapter 4Bilberry (Vaccinium myrtillus L.). Herbal Medicine: Biomolecular and Clinical Aspects. 2nd edition. Benzie IFF, Wachtel-Galor S, editors. Boca Raton (FL): CRC Press/Taylor & Francis; 2011. Retrieve from https://www.ncbi.nlm.nih.gov/books/NBK92770/
Bilberry, (2016). National Center for Complementary and Integrative Health. Retrieve from https://nccih.nih.gov/health/bilberry