Bilberry fruit and its extract contain chemical compounds known as anthocyanosides, which play a role in circulation and blood vessel strength. Bilberry may be beneficial for treating chronic venous insufficiency, according to the U.S. National Library of Medicine's MedlinePlus website. This disorder has symptoms that include leg swelling and pain, varicose veins and skin ulcers. Several side effects are associated with bilberry extract but primarily with excessive doses.
Blood Sugar Reduction
Bilberry extract can lower blood sugar levels, according to MedlinePlus. People prone to hypoglycemia should be cautious about using bilberry extract. Additionally, diabetic patients who are taking medication such as metformin or insulin to regulate blood sugar, or who are taking herbs for this purpose, may need to monitor their blood sugar more closely when using bilberry extract.
Increased Bleeding
Taking large doses of bilberry extract may raise the risk of abnormal bleeding, according to MedlinePlus. People with bleeding disorders and those who take medications or herbs that increase the risk of bleeding should be cautious about using bilberry extract. These medications include nonsteroidal anti-inflammatory drugs such as aspirin and ibuprofen, anticoagulants such as warfarin or heparin, and anti-platelet drugs such as clopidogrel. The herb ginkgo also can elevate the risk of bleeding. Individuals should discontinue using bilberry extract before undergoing surgery or dental procedures.
Gastrointestinal Effects
Large doses of bilberry extract can cause upset stomach, as explained by MedlinePlus. Bilberry also may lead to or worsen diarrhea if taken with medications that can cause loose stools, such as laxatives and certain antibiotics.
Toxicity
Another side effect associated with large doses of bilberry extract is toxicity from its components hydroquinone and tannins. The University of Maryland Medical Center cautions people not to consume large quantities of bilberry extract for extended time frames because toxicity can result in muscle spasms, vomiting and severe weight loss, and can even be life-threatening.
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