Blueberries

What it is

Blueberries are small berries of the Vaccinium genus [1]. They are rich in anthocyanins, a group of plant compounds called polyphenols [2]. Trials used fresh, frozen, wild and freeze-dried blueberries, often as a powder; a cup of fresh berries (about 150 g) was the common reference amount [3]. Bilberries are a close Vaccinium relative, grouped with blueberries and cranberries in a 2024 review [4].

How it might work

Proposed, not established: after eating blueberries, the body produces breakdown products of their polyphenols, which show up in blood and urine [5]. The authors of one blood vessel trial propose that the effect comes from less oxidative stress [5] and more nitric oxide, a signal molecule involved in artery function [6]. The authors of the midlife memory trial suggest the insulin results may be linked to anthocyanin action [7].

What the research says

Memory. A 2025 meta-analysis pooled nine randomized trials with 513 people who had mild cognitive impairment or self-reported memory decline. Episodic memory improved, with a small effect (standardised mean difference 0.34, 95% CI 0.11 to 0.57), and memory for words improved slightly in the mild impairment group (0.30, 0.01 to 0.60). Processing speed, recognition memory, visual-spatial learning and working memory showed no clear change [2]. In overweight adults aged 50 to 65 with self-reported memory decline, blueberry supplementation improved scores on word-access and memory-interference tests [7]. In a 12-week trial of 61 healthy adults aged 65 to 80, freeze-dried wild blueberry powder improved immediate recall compared with placebo [8]. A 16-week trial in older adults with mild cognitive impairment found more brain activity during a memory task, but no clear improvement in working memory itself [9].

Blood vessels. Three trials found better artery function, measured as flow-mediated dilation (how much an artery widens when blood flows more). In a 6-month trial of 115 adults with metabolic syndrome, one cup a day increased flow-mediated dilation by 1.45% (95% CI 0.83 to 2.1) and lowered augmentation index, a measure of artery stiffness, by 2.24% [3]. In 43 postmenopausal women with above-normal blood pressure, 12 weeks of blueberry powder improved flow-mediated dilation more than placebo [5]. In the 61 healthy older adults, flow-mediated dilation rose by 0.86% (95% CI 0.56 to 1.17) more than with placebo [8]. A single meal trial in 45 adults with metabolic syndrome found no change in artery function, though it did show the glucose and insulin effects below [10]. In two small crossover trials of young men, a 300 g serving improved artery function within hours [11].

Blood pressure. Results are mixed. A 2017 meta-analysis of six trials (204 people) found no significant change [1]. A 2024 review of blueberry and cranberry trials in people with heart disease also found no significant change [12]. A 2021 meta-analysis of 12 trials in people with metabolic syndrome found a significant fall in diastolic pressure [13]. In an 8-week trial of 48 postmenopausal women with pre- or stage 1 hypertension, systolic pressure fell from 138 to 131 mm Hg and diastolic from 80 to 75 mm Hg in the blueberry group, with no change in the control group [6]. In the healthy older adults, 24-hour average systolic pressure was 3.59 mm Hg lower than with placebo [8].

Blood sugar. Results are mixed. In a 2022 meta-analysis of 22 trials of blueberry or cranberry, fasting glucose fell by about 18 mg/dL in people with diabetes (95% CI -29.6 to -5.8), with no clear effect in people without diabetes [14]. The same review reported that HbA1c fell by 0.32%, but its p-value (0.15) does not match its confidence interval, so this figure is uncertain [14]. A 2022 meta-analysis of 21 studies in metabolic syndrome found no significant change in glucose, HbA1c or insulin resistance [15]. After a high-fat, high-sugar drink, adding 26 g of freeze-dried blueberries lowered glucose 3 hours later (4.3 vs 5.1 mmol/L) and insulin (23.4 vs 52.9 pmol/L), though glucose peaked higher at 1 hour (8.2 vs 6.9 mmol/L) [10]. In a trial of 34 pregnant women with obesity, whole blueberries plus soluble fiber lowered glucose on a glucose screening test (100 vs 131 mg/dL), but the two were given together, so the effect cannot be attributed to blueberries alone [16].

Cholesterol. Results are mixed. A 2021 meta-analysis of 12 trials found lower total and LDL cholesterol after blueberries [13]. A 2026 meta-analysis of anthocyanin trials, mostly not blueberry-only, found no change in lipids [17]. In a 6-month trial, one cup a day raised HDL (the protective kind) by 0.08 mmol/L in people not taking statins, while half a cup had no effect on any measure [3].

Heart attacks and heart disease. Observational studies link higher anthocyanin intake to lower heart risk, but they cannot show cause and effect. A 2026 meta-analysis of 18 cohorts found that the highest intake, compared with the lowest, was linked to 18% lower heart attack risk (5 studies) and 26% lower heart disease risk (4 studies); stroke risk was not affected [17]. These cohorts measured anthocyanins from foods in general. We did not find a blueberry-only analysis in our searches.

Exercise recovery. In 49 untrained adults, 18 days of freeze-dried blueberries (one cup a day) did not reduce muscle soreness or damage compared with placebo after a 90-minute exercise bout designed to cause soreness [18]. Among 14 runners, four days of blueberry powder lowered blood lactate after an 8 km run (5.4 vs 6.6 mmol/L) but did not change time-trial results [19]. A 2024 review of Vaccinium berries found no clear effect on exercise performance and only one study reporting a recovery benefit [4].

Eye fatigue. Bilberry is a close relative of the blueberry, and its extract has been tested for the eye strain that comes with screen work. A 2022 review of 45 computer-vision trials found berry extract supplementation did not significantly improve visual fatigue (7 trials) or dry-eye symptoms (4 trials) [20]. Two small bilberry-extract trials reported improvements instead: in 80 video-display workers, 480 mg a day for 8 weeks eased the drop in critical flicker fusion and several fatigue symptoms after screen tasks [21], and in 109 adults, 240 mg a day for 12 weeks improved an objective measure of ciliary-muscle strain after screen tasks [22].

Doses used in studies

Memory and blood vessel trials used about 22 to 26 g of freeze-dried blueberry powder a day for 8 to 12 weeks [6] [8] [5]. A 6-month trial used one cup (about 150 g fresh) or half a cup a day [3]. The single-meal trial added 26 g of freeze-dried blueberries to an energy-dense drink [10]. The exercise trial used one cup a day, providing 280 mg of anthocyanins, for 18 days [18]. The highest whole-blueberry dose we found was 280 g a day with 12 g of soluble fiber, in pregnancy [16]. These are research doses, not recommendations.

Safety and interactions

Side effects. The trial abstracts we read do not describe serious side effects. The trials were small and mostly short, so rare or long-term effects cannot be ruled out [3] [8].

Upper limits. We found no upper intake limit or toxic dose for blueberries eaten as food. The highest whole-blueberry dose in the trials we read was 280 g a day [16].

Medicine interactions. We found no clinical study of whole blueberries with blood thinners or other medicines. A 4-week study of an anthocyanin supplement (not whole fruit), at 320 mg twice a day in 55 people, reduced platelet activation, which affects clotting [23]. People taking blood thinners or antiplatelet drugs, or medicines for diabetes or blood pressure, should ask a doctor first, because blueberries lowered some of these markers in trials [10] [6].

Pregnancy and breastfeeding. One small trial gave pregnant women with obesity 280 g of whole blueberries plus 12 g of soluble fiber daily from early pregnancy; infant birth weight did not differ between groups [16]. We found no safety studies in breastfeeding.

Kidney, liver and bleeding conditions. The trials enrolled healthy older adults, people with metabolic syndrome and postmenopausal women with blood pressure concerns [8] [3] [6]. We found no trials in people with kidney or liver disease or bleeding disorders.

The bilberry-extract trials reported no severe adverse events [21].

Caveats and open questions

Most single trials here enrolled fewer than 100 people and lasted 12 weeks or less [8] [5] [6]. Industry ties: the US Highbush Blueberry Council funded or supplied the midlife memory trial [7] and the exercise trial [18], and an author of the single-meal trial advises its grant committee [10].

Forms differ. Trials used freeze-dried powders, fresh or frozen berries, wild blueberries and blueberry-cranberry mixes, so results may not carry over to every product [14] [8].

Most blood vessel, blood pressure, cholesterol and blood sugar results are measures of body function, not heart attacks, strokes or diabetes diagnoses [3]. The midlife trial measured thinking tests and metabolism, not dementia diagnosis [7].

The strongest memory evidence comes from people with mild memory decline. A 2019 review found less evidence for working memory [24]. In our searches, the healthy-adult memory evidence came from one trial [8].

Registered trials, listed on this page, are still recruiting, so their results are not yet known. The eye-fatigue trials used bilberry extract capsules, not whole blueberries, so results may not carry over to the fruit [21] [22].