Blueberry Nutrition: What Anthocyanins Actually Do

For a long time, blueberries ruled the antioxidant charts. Health magazines cited their ORAC score. Labels on blueberry products listed it like a selling point. The higher the ORAC, the healthier the food. Blueberries had a very high ORAC, so blueberries were very healthy.

The USDA quietly dismantled that entire framework in 2012.

The agency withdrew its ORAC food database, stating that “ORAC values are routinely misused by food and dietary supplement manufacturing companies to promote their products and by consumers to guide their food and supplement choices.” The problem was simple: ORAC measures free-radical-neutralizing capacity in a test tube. That number doesn’t tell you what happens inside a human body. A food can score well in a test tube and do little or nothing in vivo.

Blueberries do still have real evidence behind them. But the reason isn’t ORAC. The reason is anthocyanins.

Nutritional Profile

Blueberries aren’t a micronutrient powerhouse. A 100g serving (about two thirds of a cup) contains 57 calories, 14g of carbohydrates, 10g of sugar, and 2.4g of fiber. The vitamin numbers are modest.

The micronutrients are fine but not remarkable. Vitamin K is the one standout, which matters if you take warfarin. Ask your prescriber before making large changes to your blueberry intake. Vitamin C and E are present in amounts too small to drive any clinical effect on their own.

The last row on that table is the one worth paying attention to. At roughly 164mg anthocyanins per 100g, blueberries are among the most concentrated whole-food sources on record.

What Anthocyanins Are and What They Do

Anthocyanins are the pigments that give blueberries their color. The same family of compounds makes red cabbage red, black beans black, and elderberries purple. In plants, they function as UV protectants and attract pollinators. In humans, the story is more complicated.

Think of anthocyanins as keys that fit specific locks on cell surfaces, particularly on endothelial cells (the cells that line the inside of your blood vessels). When anthocyanins bind to those receptors, they appear to increase nitric oxide production. Nitric oxide relaxes blood vessel walls and improves blood flow. That’s the primary mechanism researchers point to when explaining the cardiovascular data.

The three main anthocyanins in blueberries are cyanidin-3-glucoside, delphinidin-3-glucoside, and malvidin-3-glucoside. Each interacts with cell receptors slightly differently. No single one is “the active compound”. The mix matters, which is one reason concentrated blueberry extracts don’t always replicate what whole blueberries do in studies.

Anthocyanins are also poorly absorbed in the small intestine. Most of what you eat reaches your colon intact, where gut bacteria ferment them into smaller metabolites. This is similar to what happens with polyphenols more broadly. The fermentation products may have their own effects on inflammation markers and cell signaling, though that evidence is earlier-stage.

What the Research Actually Shows

Cardiovascular

The strongest blueberry evidence is a 2013 prospective cohort by Cassidy et al., published in Circulation (PMID: 23319811). The study tracked 93,600 women aged 25-42 for 18 years. Women with the highest anthocyanin intake, primarily from blueberries and strawberries, had a 32% lower risk of myocardial infarction compared to women with the lowest intake. That’s a large sample, a long follow-up, and a specific food source, not a supplement.

Cohort studies can’t prove causation. Women who eat more blueberries might also have other healthy habits. The researchers did adjust for diet quality, physical activity, and other cardiovascular risk factors, and the association held. It’s not proof, but it’s among the better observational evidence in nutrition.

The proposed mechanism runs through endothelial function and blood pressure. Multiple smaller intervention trials have found that regular blueberry consumption improves flow-mediated dilation, a measure of how well arteries relax. Most of these trials used blueberry powder equivalent to one to two cups of fresh blueberries per day.

Brain Health

This is where the evidence gets thinner. Krikorian et al. (2010) published one of the most cited blueberry-brain studies in the Journal of Agricultural and Food Chemistry (PMID: 20047325). Participants were older adults with mild cognitive decline. The blueberry group received daily wild blueberry drinks for 12 weeks and showed improved performance on verbal learning and memory tests compared to placebo.

The catch: the study had nine participants. Nine. It’s a pilot study, and Krikorian’s group has published follow-ups with slightly larger samples, but the field as a whole lacks large-scale randomized trials. The cognitive benefit is biologically plausible because anthocyanins cross the blood-brain barrier in small amounts and animal studies show effects on hippocampal signaling. But “biologically plausible with small-sample pilot data” is a long way from “blueberries improve memory.” Don’t extrapolate this to Alzheimer’s prevention or treatment. The evidence isn’t there.

Gut Microbiome

Work from the Sonnenburg lab and others has shown that anthocyanins reaching the colon are fermented by specific bacterial species. This is a real and interesting mechanism, but most of it is preclinical or short-term human intervention data. It’s worth watching as a field. Right now it’s emerging evidence, not a settled finding. Gut microbiome basics has more context on how to read this kind of research.

Pterostilbene

Blueberries also contain pterostilbene, a compound chemically related to resveratrol (the compound that briefly made red wine famous). Some animal and early human studies have looked at pterostilbene for blood sugar regulation and LDL oxidation. The doses used in many studies are higher than what whole blueberries deliver, and the evidence in humans is mixed. It’s not a strong reason to eat blueberries, but it’s another bioactive compound that may contribute to effects researchers observe in the food-based trials.

Fresh vs Frozen vs Cooked

Freezing blueberries does not meaningfully reduce anthocyanin content. The cell walls rupture when frozen, which can actually increase anthocyanin extractability during digestion. Frozen blueberries are grown at peak ripeness and frozen quickly. Fresh out-of-season blueberries shipped across the country are often picked underripe and have lower anthocyanin concentrations than frozen. Frozen is the practical choice for most people most of the year.

Cooking is a different matter. Jam-making and prolonged heating reduce anthocyanins by 20-40% (see more on how cooking changes nutrients). A blueberry muffin or blueberry jam delivers fewer anthocyanins per gram than fresh or frozen berries. That doesn’t mean you can’t enjoy cooked blueberries. It just means they’re not equivalent to raw.

The practical hierarchy for anthocyanin content: fresh or frozen blueberries eaten raw are clearly better than baked or jammed.

One more thing worth saying directly: much of the blueberry research used concentrated extracts or freeze-dried powder, not fresh berries off the grocery shelf. Extracts can deliver standardized anthocyanin doses that are hard to guarantee from fresh fruit, which varies by variety, ripeness, and growing conditions. Wild blueberries (smaller, darker, typically sold frozen) have higher anthocyanin concentrations than cultivated varieties. If you’re trying to match research doses, wild frozen blueberries are a reasonable choice.