Bilberry, or Vaccinium myrtillus, is a fruit closely related to the American blueberry, and has been used for centuries in traditional European medicine and as a food. It is celebrated for its antioxidant properties, stemming from compounds called anthocyanosides, which have been studied for potential benefits for eye health, circulation, and inflammation. However, the use of bilberry supplements, especially at higher doses or over long periods, carries risks that warrant careful consideration and a clear understanding of what are the negative side effects of bilberry?.
Common and Mild Negative Side Effects
For most people, consuming bilberry fruit in typical food amounts is likely safe. However, side effects, though generally mild, can occur with the use of supplements or excessive consumption.
- Gastrointestinal Distress: Some individuals may experience mild digestive symptoms such as nausea, abdominal discomfort, gas, or diarrhea. Excessive consumption of bilberry juice or high-tannin content in the leaves can also contribute to these issues.
- Skin Rashes and Allergic Reactions: Allergic responses to bilberry can happen, with reported reactions including skin rashes. Those with sensitivities to tannins, a substance found in bilberries, should be cautious.
- Drowsiness: In some studies, a small percentage of people taking bilberry extract reported experiencing drowsiness.
- Other Potential Effects: Bilberry fruit may cause darker stools. Long-term or high-dose use of bilberry leaf has been historically associated with more severe side effects like anemia, fatigue, and jaundice, though these are rare with modern preparations.
Serious Drug Interactions and Health Risks
Bilberry's active components can interact with certain medications and affect blood sugar and clotting, posing significant risks, especially for those with pre-existing health conditions.
Bleeding and Anticoagulant Interactions
Bilberry may slow blood clotting due to its anti-platelet activity, which can increase the risk of bruising and bleeding when taken with certain medications.
- Anticoagulants and antiplatelet drugs: This includes medications like warfarin ($Coumadin$), clopidogrel ($Plavix$), and aspirin.
- NSAIDs: Combining bilberry with nonsteroidal anti-inflammatory drugs like ibuprofen or naproxen might also increase bleeding risk.
Diabetes Medication Interactions
Bilberry has been shown to lower blood sugar levels. For people with diabetes, taking bilberry supplements alongside their prescribed medication could lead to dangerously low blood sugar (hypoglycemia).
- Glucose-Lowering Medications: Patients on insulin, metformin, glyburide, glipizide, and other diabetes drugs should monitor their blood sugar closely.
- Other Herbal Supplements: Combining bilberry with other herbs that also lower blood sugar, such as ginseng, fenugreek, or garlic, can further compound this risk.
Liver Enzyme Interactions
Some medications are broken down by liver enzymes. Bilberry might alter the speed at which the liver metabolizes these drugs, potentially changing their effects and side effects. Caution is advised for those on medications processed by liver enzymes, particularly the cytochrome P450 family.
Specific Risks by Bilberry Form
The form of bilberry consumed significantly impacts its safety profile. There is a marked difference in the risks associated with the fruit versus the leaf, especially in high concentrations.
- Bilberry Fruit (Whole/Dried): Generally safe in food amounts. Risks are primarily associated with excessive intake, leading to mild digestive upset.
- Bilberry Fruit Extracts: Possibly safe for short-to-medium term use (up to 6–12 months) at recommended doses. The main concern is drug interactions with blood thinners and diabetes medication.
- Bilberry Leaf: Considered possibly unsafe, especially in high doses or for prolonged periods. The tannins in the leaves, if consumed excessively, can cause toxic side effects, including severe weight loss and muscle spasms. It is important to distinguish between bilberry fruit and leaf products.
Precautions and Contraindications
Due to safety concerns, bilberry supplementation is not recommended for certain groups.
- Pregnancy and Breastfeeding: A lack of reliable safety data means bilberry supplements should be avoided by pregnant or nursing women.
- Prior to Surgery: Because bilberry can affect blood sugar and blood clotting, it is essential to stop taking it at least two weeks before any scheduled surgical procedure.
- Children: The safety of bilberry supplements in young children is not known, and parents should consult a doctor before use.
- Unwashed Wild Berries: There is a risk of contracting a parasitic tapeworm, Echinococcus multilocularis, from consuming unwashed wild berries. Thorough washing is vital.
Comparison of Bilberry Forms and Risks
| Feature | Bilberry Fruit (Food) | Bilberry Fruit Extract (Supplement) | Bilberry Leaf (High Dose) |
|---|---|---|---|
| Primary Risk | Low (safe for most in moderation) | Drug interactions, mild GI upset | Toxicity, organ damage, severe weight loss |
| Safety Profile | Generally safe | Possibly safe for short-term use | Possibly unsafe for long-term/high-dose use |
| Interaction with Meds | Minor/theoretical | Significant risk with blood thinners and diabetes medications | Significant risk with blood thinners and diabetes medications |
| Key Compounds | Anthocyanins, Vitamin C, Tannins | Concentrated anthocyanins | High tannins |
Minimizing Risks and Responsible Use
To minimize potential negative effects, follow these guidelines:
- Consult a Healthcare Provider: Always speak with a doctor or pharmacist before starting any new herbal supplement, especially if you have pre-existing conditions or are on other medications.
- Stick to Reputable Brands: Choose supplements from reliable sources with clear labeling regarding ingredient standardization and purity.
- Limit High Doses and Long-Term Use: Avoid taking bilberry supplements in high doses or for extended periods without medical supervision.
- Be Aware of Interactions: Understand the specific medications that may interact with bilberry and monitor yourself for any adverse symptoms.
Conclusion
While bilberry offers potential benefits, understanding what are the negative side effects of bilberry? is crucial for safe consumption. The mild gastrointestinal effects are a minor concern for most, but the serious risks involving drug interactions with anticoagulants and diabetes medications require careful medical oversight. Furthermore, bilberry leaf, particularly in high doses, carries significant toxicity risks and should be avoided. By distinguishing between the generally safe consumption of bilberry fruit as food and the more cautious use of concentrated supplements, and consulting a healthcare professional, individuals can make informed decisions about its place in their diet.
For more information on bilberry and its safety, you can visit authoritative sources like the National Center for Complementary and Integrative Health (NCCIH).
