Are blueberries really that special?

7 min read

Blueberries are sometimes called a "superfood." Antioxidant. Good for the brain. Good for blood vessels. Anti-aging. Search, and you'll find all sorts of claimed benefits.

So how much has actually been confirmed in research on people?

The short answer: what's most consistently shown for blueberries is an effect on blood vessel function. For cognition, blood pressure, blood sugar, gut health and so on, research results don't all agree.

Blueberries aren't a magic food. But the compounds in that small fruit may affect the human body.

What sets blueberries apart: anthocyanins

The main compounds behind blueberries' blue-purple color are anthocyanins. They're a type of polyphenol, also found in blackberries, red cabbage and others.

What matters is that it isn't as simple as "they're antioxidants, so they directly neutralize free radicals."

After you eat them, anthocyanins circulate in the blood as metabolites such as phenolic acids. A research group at King's College London showed that these metabolites may mediate improvements in vessel function. Purified anthocyanins improved endothelial function in a dose-dependent way, while a control drink containing only the fiber, minerals and vitamins had no significant effect. Of 63 metabolites in the blood, 14 correlated with acute and 21 with chronic improvements in FMD [1].

The strongest case: blood vessels

Lining the inside of blood vessels is tissue called the vascular endothelium. It's key to widening and narrowing vessels as needed. The main measure of this function is FMD (flow-mediated dilation).

A 2024 meta-analysis (11 studies) pooling the effects of blueberries found that FMD improved by an average of +1.50% [2]. But variation between studies was large (I² = 87%), so the number should be read as "only an average tendency."

A study of eating them for 12 weeks

There's an RCT in which 61 healthy people aged 65–80 took 26 g of freeze-dried wild blueberry powder (about 302 mg of anthocyanins) daily for 12 weeks [3].

What was used was powder, not fresh fruit. That distinction matters. Still, it's a result showing that eating blueberries daily may affect vessel function.

"Good for the brain" still calls for caution

A 2020 systematic review assessed 11 papers (12 studies), with participants ranging from children to older adults. Eight studies reported improvements on cognitive tasks, especially short- and long-term memory and spatial memory. On mood, though, one study reported significant improvement and four reported none [4]. The 12-week RCT above also reported improvements in cognition alongside vessel function [3].

But participants, amounts, durations, and cognitive tests differed between studies. So for now, we can't say "eat blueberries and you'll get smarter." The accurate statement is "there are promising results on some cognitive tasks, but no firm conclusion."

Blood pressure: results vary by study

In the 12-week RCT above, systolic blood pressure fell by about 3.6 mmHg [3]. But the upper end of the 95% confidence interval was −0.23 mmHg, close to zero. Line up other studies, and results don't agree.

The effect on endothelial function is fairly consistent. The effect on blood pressure varies by study and measure.

What about blood sugar?

In a 6-month RCT of adults with metabolic syndrome, insulin resistance, pulse wave velocity, blood pressure, and nitric oxide did not change [5]. In other words, we can't say "eat blueberries every day and your insulin resistance will improve." In the same study, the group eating the equivalent of about 150 g a day did show improvements in some cardiovascular measures, including vessel function [5].

They may affect gut bacteria too

Some blueberry polyphenols aren't absorbed in the small intestine and reach the large intestine, where gut bacteria metabolize them. So the relationship between blueberries and gut bacteria has also been studied.

Both are small studies. Even if particular bacteria change, we can't conclude that the gut environment as a whole improved.

Does processing make them pointless?

In a crossover trial with 10 healthy people, a baked good made with blueberries was compared with an unprocessed drink made with the same amount of powder. The baked good had about 42% fewer anthocyanins. Even so, FMD up to 6 hours after eating rose about as much with the baked good as with the unprocessed drink [8].

But this result is limited to 10 people and the acute response up to 6 hours. This study can't tell us whether long-term effects would be the same with processed foods.

So what's actually special about blueberries?

Don't mix these up.

There's no need to think of blueberries as "a magic food that makes you healthy." What's more interesting is that RCTs have found measurable changes in vessel function just from eating an ordinary food regularly.

It's not medicine. Not a special supplement. A small fruit sold in the supermarket. And still, something is happening inside the body.

How much should you eat?

The research can't pin down an "optimal amount." The amounts and forms used vary.

So we can't yet draw a line like "eat X g a day and you'll get this effect." Realistically, rather than treating blueberries as a special medicine, it's reasonable to think of including them regularly in your diet as one fruit option among others.

Summary

They don't work for everything. Some studies find no effect. Still, for endothelial function, multiple randomized controlled trials and meta-analyses provide evidence of improvement. On the other hand, cognition, blood pressure, metabolism, and gut health still need cautious evaluation.

Maybe what's special about blueberries isn't being a "miracle superfood." It's that, ordinary fruit as they are, trials in people have actually measured changes in the body.