Bilberry: Benefits, Forms, Dosing, and Side Effects

Table of Contents

• Current evidence position
• Key safety points
• Brad's videos on this topic
• Overview
• Forms and Bioavailability
• Evidence for Health Benefits
• Recommended Dosing
• Safety and Side Effects
• Drug Interactions
• Dietary Sources
• References

Current evidence position

Brad has not made a video on this topic; this is a summary of the evidence, not his view. Bilberry has not been clearly shown to help any health condition, and a 2022 review found contradictory results for its three most cited uses, type 2 diabetes, vision and circulation, with no clear conclusion on benefit or dose ^{[1, 9]}. Its best-known claim, better night vision, has not held up: the 4 most recent randomized trials in a 2004 systematic review were negative, and the most rigorous studies found no benefit in healthy people ^{[9, 11]}. Small trials suggest possible effects on dry eye, eye strain from screens and blood sugar after a meal, but larger double-blind trials are lacking ^{[1, 25, 40, 41]}. Bilberry may raise bleeding risk in people taking blood thinners and may lower blood sugar, so people on anticoagulants, aspirin or diabetes medicines should talk to their doctor first ^{[25, 45, 46]}.

Brad's videos on this topic

None yet.

1. Overview

Bilberry (Vaccinium myrtillus) is a shrub native to northern Europe, the northern United States and Canada, and its dark berries resemble blueberries ^[9]. Compared with a cultivated blueberry, bilberry fruit holds much more anthocyanin, particularly in the flesh ^[6].

Anthocyanins are pigments that give many fruits their blue, purple and red colour ^[15]. Bilberries also contain anthocyanosides, tannins and flavonoids ^[9].

Extracts of bilberry fruits and leaves have traditionally been used for vision, high blood sugar and several heart and circulation problems ^[9]. Today, fruit extracts appear in eye health supplements, while leaf extracts are sold for type 2 diabetes and blood sugar control ^[1].

The best-known claim concerns night vision. British pilots in World War II reportedly ate bilberry jam, thinking it would help them see at night; the story may have been superstition or a deliberate hoax to hide improvements in radar, but it prompted research on bilberry and night vision ^[9]. The most rigorous of those trials found no benefit ^{[11, 37, 38, 39]}.

Bilberry has not been clearly shown to help any health condition, and many studies were too small or poorly designed to reach firm conclusions ^[9]. A 2022 review traced the vision and diabetes claims to unproven or false claims repeated in research since the 20th century without consistent fact-checking ^[1].

Nutritional Profile

Bilberries and blueberries are among the best sources of flavonoids, especially anthocyanins, and bilberry's anthocyanin content is much higher than that of the blueberry it was compared with ^[6].

2. Forms and Bioavailability

Standardized Extracts

Trials have used concentrated extracts. A type 2 diabetes study used a standardized extract with 36% anthocyanins, and its single 0.47 g capsule equalled about 50 g of fresh bilberries ^[25]. A dry eye trial used Mirtoselect, a standardized extract made from fresh frozen bilberries ^[40]. A night vision trial used 160 mg capsules of an extract with 25% anthocyanosides ^[37].

Understanding Label Claims

Labels usually state an extract's strength as a percentage of anthocyanins or anthocyanosides, and trials have used different standards, such as 36% anthocyanins ^[25] and 25% anthocyanosides ^[37]. A product's strength therefore depends on both the amount of extract and the percentage claimed.

Concentration Ratios: Why They Matter

Labels can overstate strength. In one laboratory analysis, about 60% of bilberry extracts and 33% of finished supplements contained less anthocyanin than declared ^[43].

Anthocyanin Bioavailability

Anthocyanins follow a different path through the body from other flavonoids ^[15].

Absorption: Anthocyanins can be absorbed from the stomach as well as the intestines, and active transporters may help ^[15]. In a rat experiment testing absorption from the stomach, a grape anthocyanin appeared in the blood after only 6 min ^[16].

Metabolism: Some anthocyanins are absorbed intact and then undergo extensive first-pass metabolism, entering the circulation as metabolites ^[15].

Gut microbiome: Some anthocyanins reach the large intestine in significant amounts, where gut bacteria break them down. Phenolic acid metabolites reach much higher blood levels than the parent anthocyanins and may account for some of the health effects linked to them ^[15].

Matrix effects: The rest of the extract may matter. In rats, Mirtoselect produced a larger plasma anthocyanoside area under the curve (202.34 µg·min/ml) than a highly purified anthocyanin extract (130.93 µg·min/ml), even though the purified extract was given at a much higher anthocyanin dose ^[40].

Forms Available as Supplements

Species Confusion

Check that the label names Vaccinium myrtillus. Bilberries are expensive, and testing has found supplements falsified with anthocyanins from other sources ^[44], in one study mainly mulberry and chokeberry ^[43]. In one study, 45% of bilberry supplements were of unacceptable quality, including products with no bilberry at all ^[44]. Independent testers such as ConsumerLab.com and Labdoor publish product testing.

3. Evidence for Health Benefits

Retinopathy (Diabetic and Hypertensive)

A 2022 review found that vision trials gave contradictory results with no clear conclusion on benefit or dose, and that the vision claims arose from unproven or false claims ^[1].

Bilberry has not been clearly shown to help any health condition, including retinopathy ^[9].

Night Vision

This is bilberry's most famous claim, and rigorous trials do not support it.

The WWII legend: NCCIH notes that the story of pilots eating bilberry jam may have been superstition or a deliberate hoax to conceal improvements in radar ^[9].

Systematic review: A 2004 systematic review found 30 trials with outcomes relevant to vision in low light, of which 12 were placebo-controlled ^[11]. The 4 most recent were randomized and negative. One other randomized trial and 7 non-randomized controlled trials reported benefits, but negative results went with more rigorous methods, as well as lower doses and extracts from different regions ^[11]. The reviewers concluded that rigorous studies do not support the idea that bilberry improves normal night vision, and that no rigorous research has tested people whose night vision is impaired by eye disease ^[11].

Individual trial results: In 16 healthy young volunteers, single doses of 12, 24 and 36 mg of anthocyanosides had no effect on any of three night vision tests during the 24 h after the dose ^[39]. In 18 volunteers, regimens of 12 and 24 mg anthocyanosides twice a day for 4 days also had no effect ^[38]. In young men with good vision, one 160 mg capsule of bilberry extract, standardized to 25% anthocyanosides, three times a day for 21 days did not change night visual acuity or contrast sensitivity ^[37].

Synthesis: Bilberry has not been shown to improve night vision in healthy people ^{[9, 11]}.

Dry Eye Syndrome

Trials of bilberry for dry eye are small.

Key trial: In a randomized, double-blind, placebo-controlled trial, 22 people with dry eye symptoms took Mirtoselect or placebo for 4 weeks ^[40]. Tear secretion on Schirmer's test improved in the bilberry group (p=0.019) but not in the placebo group, and a blood test of antioxidant potential also improved (p=0.003) ^[40]. Only 21 people completed the study.

Eye strain from screens: In office workers who used screens, 480 mg/day of bilberry extract for 8 weeks lessened the screen-induced drop in one eye fatigue test and eased several fatigue symptoms more than placebo; a second measure, near point accommodation, did not improve ^[41]. A 12-week trial in 109 healthy adults gave 240 mg of standardized extract or placebo each day; the extract group did better on a measure of focusing-muscle strain after screen tasks ^[42].

Metabolic Health: Blood Sugar and Insulin Sensitivity

Human evidence on blood sugar is limited to small studies.

Blood sugar effects: In diabetic rats, a bilberry leaf extract given for 4 days lowered plasma glucose by about 26% ^[33]. Leaf extracts are sold for type 2 diabetes, but a 2022 review traced the diabetes claims to unproven or false claims and found contradictory trial results ^[1].

Human evidence: In 8 men with type 2 diabetes managed by diet and lifestyle, a single 0.47 g capsule of standardized extract (36% anthocyanins) before a starch drink lowered the rise in blood glucose (P = 0.003) and insulin (P = 0.03) compared with placebo ^[25]. The authors suggest bilberry may slow how fast carbohydrate is digested or absorbed ^[25].

Insulin sensitivity: The single-dose study measured the insulin response to one drink, not insulin sensitivity over time ^[25].

Reviews: A 2020 review concluded that any benefit of bilberry supplements in people who have type 2 diabetes or cardiovascular disease still needs to be clarified in large clinical trials ^[12].

Bilberry leaf vs. fruit: Fruit and leaf differ. Leaves contain high amounts of proanthocyanidins, flavonols and hydroxycinnamic acids ^[6], and the animal blood sugar data come from leaf extract ^[33]. Bilberry leaves may be unsafe in high doses or for long periods ^[9].

Cardiovascular and Vascular Health

Blood Vessel Integrity and Chronic Venous Insufficiency

Bilberries are used for symptoms of varicose veins ^[44]. A 2022 review found contradictory results for circulatory diseases, with no clear conclusion on benefit or dose ^[1]. Bilberry has not been clearly shown to help any health condition ^[9].

Lipid Profiles

A 2022 review found beneficial clinical results for dyslipidemia (abnormal blood fats) with fresh bilberries or anthocyanin-rich fruit extracts, but noted a general lack of larger double-blind controlled trials ^[1]. In rats, a leaf extract lowered plasma triglycerides by 39% in diabetic animals ^[33].

Platelet Aggregation

Bilberry is one of several herbs reported to have antiplatelet activity ^[45]. This may matter for bleeding in people who also take blood thinners or NSAIDs (see Safety section).

Anti-Inflammatory and Antioxidant Effects

A 2022 review found beneficial clinical results in chronic inflammatory disorders with fresh bilberries or anthocyanin-rich extracts, again with a lack of larger double-blind trials ^[1]. Antioxidant results differ by study: in the dry eye trial, blood antioxidant potential improved ^[40], while the single-dose diabetes study found no change in two antioxidant measures ^[25].

Kidney Health

Bilberry has not been clearly shown to help kidney health, or any other health condition ^[9].

Skin Health

No skin benefit has been shown in people; NCCIH finds bilberry has not been clearly shown to help any health condition ^[9].

Mood and Cognitive Function

Bilberry has not been shown to improve mood or memory in people ^[9].

Other Traditional and Proposed Uses

Bilberry is used for other conditions, but it has not been clearly shown to help any health condition ^[9]:

• Diarrhea: Bilberries are used for non-specific diarrhea ^[44]
• Varicose veins: Bilberries are used for related symptoms ^[44]

4. Recommended Dosing

Clinical Trial Doses

There is no established dose. Trials have used these amounts:

Standard Dosing Recommendations

No dose has been shown to treat any condition. NCCIH notes that bilberry fruit extracts have been used safely in research studies at doses of up to 160 mg/day for up to 6 months ^[9].

Timing and Administration

Trials have given bilberry extract once, twice or three times a day ^{[37, 38, 42]}. The diabetes study gave a single capsule followed by a starch drink ^[25].

How to Read a Bilberry Supplement Label

The most important factors to verify on a bilberry supplement label:

1. Species: Confirm Vaccinium myrtillus; testing has found products made with other plants ^{[43, 44]}
2. Standardization: Look for a stated anthocyanin or anthocyanoside percentage, as trials used ^{[25, 37]}
3. Dose per serving: Multiply the extract amount by its percentage to estimate the anthocyanins per serving

5. Safety and Side Effects

General Safety Profile

Bilberry fruit is considered safe in amounts typically found in foods ^[9]. Bilberry fruit extracts have been used safely in research studies at doses of up to 160 mg/day for up to 6 months and appear to be well tolerated ^[9]. In an 8-week trial of 480 mg/day, there were no severe adverse events ^[41].

Reported Side Effects

Fruit extracts appear to be well tolerated ^[9].

• Allergic reactions: Possible. For trouble breathing, swelling of the face or throat, or fainting, call your local emergency number (111 in NZ, 000 in Australia, 911 in the US, 999 in the UK) or go to the emergency department.

Blood Sugar Effects

A single dose of bilberry extract lowered the rise in blood glucose and insulin after a starch drink in men with type 2 diabetes ^[25]. This could add to the effect of diabetes medicines.

People with diabetes, or on blood sugar-lowering medicines, should talk to their doctor before taking bilberry and check their blood sugar more often ^{[9, 25]}. If someone with diabetes is unconscious, having a seizure, or cannot swallow safely, call your local emergency number (111 in NZ, 000 in Australia, 911 in the US, 999 in the UK). Do not give food or drink by mouth.

Antiplatelet Effects

Bilberry is one of several herbs reported to have antiplatelet activity, and with NSAIDs, particularly aspirin, such herbs may raise the risk of bleeding ^[45]. A 2022 review of supplements and bleeding found bilberry associated with bleeding risk in people taking anticoagulants, but no evidence of bleeding without them ^[46]. If you take a blood thinner, aspirin or another NSAID, talk to your doctor before using bilberry. For signs of a stroke or bleeding in the brain (face drooping, arm or leg weakness or numbness, trouble speaking, vision loss, even if it passes, or a sudden severe headache), call your local emergency number (111 in NZ, 000 in Australia, 911 in the US, 999 in the UK). Call it too for bleeding that will not stop.

Surgery

A 2022 review advises stopping non-essential supplements, such as bilberry, 2 weeks before planned surgery ^[46].

Bilberry Leaf Safety

Bilberry leaf safety is less established than bilberry fruit safety ^[9]:

• Long-term use: Bilberry leaves may be unsafe when consumed in high doses or for long periods of time ^[9]
• Blood sugar: A leaf extract lowered blood sugar in diabetic rats ^[33]. If you have diabetes, talk to your doctor before using bilberry leaf.
• Lack of human data: Bilberry leaf extract has not been tested in rigorous human safety studies

Special Populations

• Pregnancy and breastfeeding: Little is known about whether it is safe to use bilberry in amounts greater than those found in foods during pregnancy or while breastfeeding ^[9]

6. Drug Interactions

Anticoagulant and Antiplatelet Medications

Bilberry's reported antiplatelet activity, and its link with bleeding in people taking anticoagulants, call for caution with blood-thinning medicines ^{[45, 46]}:

If you take any type of medicine, talk with your health care provider before using bilberry; some herbs and medicines interact in harmful ways ^[9].

Blood Sugar-Lowering Medications

Bilberry extract lowered the blood sugar response to a starch drink ^[25], so it may add to diabetes medicines:

Other Potential Interactions

• Drug absorption: In cells, bilberry extract blocked a gut transporter (OATP-B) that carries some medicines by 75.5%, and the authors suggest some supplements may reduce the absorption of drugs that use it ^[47]. Whether this matters in people is unknown. If you take prescription medicines, check with your doctor or pharmacist before starting.

7. Dietary Sources

Fresh Bilberries

Bilberry grows wild in northern Europe, the northern United States and Canada ^[9]. Its fruit is an important part of local diets in many countries ^[1]. Compared with blueberries, bilberries hold much more anthocyanin, particularly in the flesh, while blueberries are dominated by hydroxycinnamic acids ^[6].

Wild Harvesting and Availability

Bilberries are quite expensive fruits, which creates a motive for fraud in bilberry supplements ^[44].

Food Forms

Bilberries are sold fresh, dried and as juice ^[44]. In one quality study, 91% of dried bilberries from different sources and three representative juices were of good quality, while many supplements were not ^[44].

How Processing Affects Anthocyanin Content

Improper drying or storage can lower the quality of bilberries, and laboratory tests can detect it ^[44].

Comparison with Other Anthocyanin-Rich Foods

Bilberries and blueberries are among the best sources of anthocyanins, and bilberry has much higher levels than the blueberry it was compared with ^[6]. Extracts of mulberry and chokeberry, also rich in anthocyanins, have been used to adulterate bilberry extracts ^[43].