In the longest trial of its kind, a team at the University of East Anglia and Harvard tracked 138 adults with metabolic syndrome. Each ate a cup of blueberries, about 150 grams, every day for six months.
The result was measurable improvements in blood vessel function and arterial stiffness. The researchers estimated the changes would translate to a 12 to 15 percent lower risk of cardiovascular disease.
A half-cup portion produced no measurable benefit in the same at-risk group. Only the full cup was enough, the researchers reported in 2019.
The findings sit inside a broader body of nutrition research that keeps returning to the same small, deep-blue fruit. Below is what the strongest studies suggest for four different systems.
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What six months of daily blueberries did to blood vessels
The University of East Anglia and Harvard trial, led by Prof. Aedin Cassidy and Dr. Peter Curtis, measured arterial stiffness and flow-mediated dilation, two markers used to predict future cardiovascular events.
A separate one-month trial in 40 healthy men, reviewed by Harvard Health, found that a daily cup of wild blueberries lowered systolic blood pressure by about 5 mmHg on average.
Flow-mediated dilation, an early indicator of vessel health, improved within two hours of the first serving and held after one month.
Neither trial is proof that eating berries will prevent a heart attack. Both point to short-term changes in vascular function that, over time, are associated with lower cardiovascular risk.
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The Harvard diabetes cohort finding
For metabolism, the strongest evidence comes from Harvard's long-running observational studies. Researchers pooled data from more than 187,000 participants in the Nurses' Health Study, Nurses' Health Study II and the Health Professionals Follow-Up Study.
Adults who ate at least two servings of blueberries a week had a 23 percent lower risk of type 2 diabetes than those who ate less than one serving a month.
The lead author, Isao Muraki of the Harvard School of Public Health, and colleagues published the findings in the BMJ in 2013. Fruit juice moved in the opposite direction, with higher intake linked to a higher risk.
A slower rate of memory decline in older women
Cognition has been studied mostly in women. A review in Advances in Nutrition summarizing a decade of research pointed to a prospective study of about 16,000 older women.
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Greater intake of blueberries and strawberries was linked to slower rates of cognitive decline, with an estimated delay of about 2.5 years.
The finding is an association, not a treatment claim, and covers a group who had been eating berries regularly for years before their memories were tested.
Why the color may be doing the work
The compounds most often credited are anthocyanins, the pigments that give blueberries their color. The review reported that anthocyanins can account for up to 60 percent of the polyphenols in ripe blueberries.
They are studied for their anti-inflammatory and antioxidant effects on blood vessels and blood sugar control.
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In one 24-week trial cited in the review, higher anthocyanin intake was linked to a drop in high-sensitivity C-reactive protein, a common marker of low-grade inflammation.
None of the trials frame a daily portion of blueberries as a treatment. The message from the researchers is more modest.
A regular serving may add up over months and years, alongside the rest of the diet. People with high blood pressure, diabetes or memory concerns should keep discussing management with their doctor.
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This article is made and published by Jesper Bengtson, who may have used AI in the preparation.