Benefits
Eye focusing and eye strain after screen work
In a 12-week trial of 109 healthy adults aged 20 to 60, 240 mg a day of a standardized bilberry extract improved an objective measure of focusing-muscle strain after screen tasks compared with placebo. In an 8-week trial of 80 office workers, 480 mg a day eased several eye fatigue symptoms, though one focusing test did not differ. Both trials were run by the extract makers.
Night vision and seeing in dim light
This is bilberry's best-known use, but the evidence does not back it. A review of 12 placebo-controlled trials found the 4 most recent randomized trials negative, with positive results mostly from weaker studies. A crossover trial giving 480 mg a day for 3 weeks to young men with good vision found no change in night visual acuity or contrast sensitivity.
Post-meal blood sugar response
In 8 men with type 2 diabetes managed by diet, a single 470 mg capsule of a 36% anthocyanin bilberry extract taken before a glucose drink lowered the rise in blood sugar and insulin compared with placebo. Longer use was less clear: in 20 adults with type 2 diabetes, 1.4 g a day for 4 weeks did not change HbA1c compared with placebo.
Oxidized LDL and walking distance
In an 8-week open-label trial in 50 adults starting usual care after a heart attack, 40 g a day of freeze-dried bilberry powder lowered oxidized LDL by about 20% and added 38 m to a 6-minute walk versus usual care alone; the main inflammation marker (hs-CRP) and total and LDL cholesterol did not differ. Placebo-controlled trials in adults with raised cholesterol and in type 2 diabetes found no change in blood lipids.
Blood antioxidant markers
Bilberry is one of the richest natural sources of anthocyanins. In people, an open-label trial after a heart attack found lower oxidized LDL with bilberry powder than with usual care, though a broader antioxidant activity measure did not differ. Antioxidant potential rose within the bilberry group of a dry eye trial, while a single-dose study and a 4-week trial in type 2 diabetes found no change in antioxidant status versus placebo.
Mechanism of action
Eye focusing muscle
The 12-week trial measured fast fluctuations of the eye's focusing (ciliary) muscle, a sign of strain during near work. The authors suggest bilberry anthocyanins relieve this tension, but how they would do so has not been shown.
Light-sensing pigment and the night vision idea
The night vision claim rests on proposed effects of anthocyanins on the retina's light-sensing pigment. Controlled human trials have not shown better night vision, so this idea has not been confirmed in people.
Slower carbohydrate digestion and absorption
In the single-dose glucose study, gut hormones such as GLP-1 and GIP did not change, and the authors suggest bilberry polyphenols instead slow carbohydrate digestion or absorption. This is a proposed explanation rather than a measured one.
Antioxidant activity
Bilberry anthocyanins are described as antioxidants. In people, oxidized LDL fell versus usual care in one open-label trial, though that trial's broader antioxidant activity measure did not differ; a blood antioxidant measure rose within the bilberry group of one small trial; and antioxidant measures did not differ from placebo in two other trials.
Clinical trials
Randomized, double-blind, placebo-controlled, parallel-group, 12 weeks; funded by the extract maker, Omnica, which employs two of the authors (Kosehira et al. 2020, Nutrients)
109 healthy adults aged 20 to 60; 240 mg a day of a standardized bilberry extract or placebo
After screen tasks, an objective measure of focusing-muscle strain (HFC-1) was better with bilberry than placebo at weeks 8 and 12, and the change across the task was better at weeks 4 and 12. The outcome is a physiological measure rather than vision or symptoms.
Randomized, double-blind, placebo-controlled, 8 weeks; conducted by the supplement maker, Wakasa Seikatsu, which employs two of the authors and funds other work by two more (Ozawa et al. 2015, Journal of Nutrition, Health and Aging)
88 Japanese office workers aged 20 to 40 who used screens were enrolled and 80 finished; 480 mg a day of bilberry extract or placebo
Bilberry reduced the screen-induced drop in flicker fusion frequency and eased eye fatigue sensation, eye pain, heaviness and discomfort more than placebo at 8 weeks. Near point focusing did not differ between groups. No severe adverse events occurred.
Double-blind, placebo-controlled crossover, 3 weeks per phase with a 1-month washout; outcomes were night visual acuity and night contrast sensitivity (Muth et al. 2000, Alternative Medicine Review)
15 young men with normal sight; 160 mg of bilberry extract (25% anthocyanosides) three times a day
Neither outcome differed between bilberry and placebo at any measurement point. The trial found no benefit at this dose.
Randomized, double-blind, placebo-controlled crossover with a 2-week washout; funded by the Scottish Government (RESAS); Indena supplied the extract and the authors reported no conflicts; other outcomes included gut hormones and plasma antioxidant capacity (Hoggard et al. 2013, Journal of Nutritional Science)
8 men with type 2 diabetes managed by diet and lifestyle; one 470 mg capsule of a 36% anthocyanin extract (Mirtoselect) before a drink equal to 75 g of glucose
Compared with placebo, bilberry lowered the rise in blood glucose and insulin after the drink. The other measured blood markers did not differ from placebo. This tested one dose in a very small group.
Randomized, double-blind, placebo-controlled crossover, 4 weeks per phase with a 6-week washout; outcomes included body weight, blood pressure, blood lipids, HbA1c, antioxidant status, oxidative stress and inflammation markers (Chan et al. 2021, Phytotherapy Research)
20 Chinese adults with type 2 diabetes; 1.4 g a day of bilberry extract
None of the measured outcomes differed from placebo, including the small HbA1c drop seen during the bilberry phase.
Open-label randomized trial, 8 weeks, bilberry powder plus usual care versus usual care alone with no placebo; funded by the Orebro University Hospital Research Foundation; the authors declared no conflicts (Arevström et al. 2019, Nutrition Research)
50 adults who finished (42 men, median age 68), starting within 24 hours of a procedure to reopen a heart artery (PCI) after a heart attack; 40 g a day of freeze-dried bilberry powder, about 480 g of fresh berries
Compared with usual care alone, oxidized LDL (a marker of LDL oxidation) was about 20% lower and the 6-minute walk distance rose 38 m more. The main blood marker, hs-CRP, and total and LDL cholesterol did not differ between groups. Patients knew their group, which the authors say may bias the walk test. No adverse events were reported with bilberry.
Randomized, double-blind, placebo-controlled, three-arm crossover, 28 days per arm, in adults with elevated cholesterol; outcomes were total, LDL and HDL cholesterol, triglycerides, ApoB, fasting glucose and HDL function; anthocyanins bought from Beijing Ginko Group; funded by the UK BBSRC; the authors declared no conflicts (Aboufarrag et al. 2022, Molecular Nutrition and Food Research)
52 hyperlipidemic adults who finished; 320 mg a day of purified bilberry anthocyanins, purified black rice anthocyanins, or placebo
Neither anthocyanin treatment changed any measured outcome compared with placebo. No serious adverse events were reported.
Randomized, double-blind, placebo-controlled, 4 weeks; five of the seven authors list affiliations with Indena, the maker of Mirtoselect, and another is an Indena consultant; a blood antioxidant measure (BAP) rose within the bilberry group with no between-group test reported (Riva et al. 2017, European Review for Medical and Pharmacological Sciences)
22 otherwise healthy adults with dry eye symptoms (21 finished); 160 mg a day of Mirtoselect or placebo
Tear volume on the Schirmer test rose within the bilberry group but not with placebo; the gain versus placebo was significant for the right eye only, and larger in people with more severe dryness. Pupil constriction did not change.