Blueberries showed no link to heart attacks or strokes in 38,088 women over 28 years

Blueberries have spent more than a decade with a reputation as a heart food. One reason is January 2013. A study of young and middle-aged American nurses was announced that month with the news that women eating three or more servings of blueberries and strawberries a week may have cut their heart attack risk by as much as one-third. The berries’ red and blue pigments, called anthocyanins, were the suspected reason.

A much longer study of older women has now looked for the same benefit and not found it. In the Women’s Health Study, 38,088 women reported their diets in the early 1990s and were then followed for a median of 28 years. Those who ate more anthocyanins, or more blueberries, had no fewer heart attacks, strokes or deaths from heart disease than those who ate less, once their other habits and health had been taken into account. Those who ate more anthocyanins did tend to have better levels of two blood fats.

The analysis, with Sarah Jaehwa Park as first author and Howard Sesso as senior author, was published on October 10 in the Journal of the American Heart Association.

What the 2013 study found about berries and heart attacks

Anthocyanins belong to the flavonoids, a large family of plant compounds. They act as pigments in red and blue fruits, which is why they turn up in blueberries, strawberries and blackberries. Interest in them for the heart comes partly from short trials in which they appeared to help blood vessels widen.

The 2013 study, led by Aedin Cassidy at the University of East Anglia with colleagues at Harvard, followed 93,600 women aged 25 to 42 in the Nurses’ Health Study II for 18 years, during which 405 cases of heart attack were reported. Women in the top fifth of anthocyanin intake had a 32% lower risk than those in the bottom fifth. The estimate for blueberries and strawberries specifically was similar in size but less certain. Women eating more than three servings a week had somewhat fewer heart attacks, but the range of plausible values ran from a large benefit to a slight increase in risk, so the difference could have been chance.

In the paper, the authors wrote that a high intake of anthocyanins may reduce heart attack risk, and they called for trials to test it. “We have shown that even at an early age, eating more of these fruits may reduce risk of a heart attack later in life,” Cassidy said at the time. “This simple dietary change could have a significant impact on prevention efforts,” said the senior author, Eric Rimm.

How the Women’s Health Study tested the berry claim

The Women’s Health Study started in the early 1990s as a clinical trial, which gave 39,876 initially healthy women aged 45 or older either low-dose aspirin or a dummy pill at random. The researchers kept following the women long after the trial ended. Because the women had been checked for heart attacks and strokes for decades, the cohort is well suited to asking how everyday diet relates to heart disease.

For the new analysis, the team took the 38,088 women who filled in a food frequency questionnaire at the start, between 1992 and 1995. From it they estimated how many anthocyanins each woman ate, in total and in six chemical subtypes, and how many blueberries. They then tallied heart attacks and strokes that did not kill, and deaths from cardiovascular disease, including only those that had been confirmed. Over a median 28 years of follow-up the team recorded 2,752 confirmed major adverse cardiovascular events, to give them their formal name. That is close to seven times as many events as the 405 heart attacks in the 2013 analysis. The two counts are not of the same thing, since the new one also includes strokes and heart deaths, but the larger number gives the new study more power to detect a modest effect.

Diet was measured once, at the start, and nobody was assigned to eat berries. So the study can show whether women who ate more of them went on to have fewer heart problems, but not whether the berries were the reason.

How the blueberry link to heart disease disappeared

The first comparison looked like good news for berries. Allowing only for age, total calories and which trial pills each woman had taken, women in the four higher fifths of anthocyanin intake had a risk of heart attack, stroke or heart death between 12% and 21% lower than women in the lowest fifth.

One feature of that pattern was already a warning sign. The risk did not keep falling as intake rose: the women who ate the most anthocyanins had a smaller advantage than those in the middle, and the researchers found no trend across the fifths. A food that protects the heart would usually be expected to protect more at higher doses.

The second step removed the apparent benefit. When the team also took account of the women’s clinical, lifestyle, and dietary factors, such as their health at the start, their habits and the rest of what they ate, the differences shrank to the point where they were no longer statistically meaningful. The same was true for each of the six anthocyanin subtypes, for blueberries on their own, and for heart attacks, strokes and heart deaths taken separately.

That is a familiar pattern in nutrition research. Women who eat more fruit tend to differ from women who eat less in many ways that affect the heart, from exercise and smoking to weight and the rest of their diet. A crude comparison credits the fruit with all of those differences. Adjusting for them is imperfect, since some habits are measured roughly and others not at all, but here it was enough to remove the apparent benefit.

The team did find something in the blood. In a subset of 26,912 women who gave a blood sample at the start, those who ate more anthocyanins, across every subtype but one, had lower odds of an unhealthy level of HDL, the so-called good cholesterol, and of triglycerides, a type of blood fat. The team also measured a blood marker of inflammation; the links it reported were for the two blood fats. Because diet and blood were measured at the same moment, the blood-fat result cannot show which came first, and better blood fats did not translate into fewer heart attacks over the following decades.

How other studies of blueberries and heart disease compare

The new result does not stand alone, and it does not settle the question either. The most recent pooled analysis, published in 2026 in the American Journal of Clinical Nutrition, drew on results across 18 cohorts in 27 publications. People with the highest anthocyanin intake had an 18% lower risk of heart attack and a 26% lower risk of cardiovascular disease than those with the lowest. Its authors rated that cohort evidence as moderate, and stroke risk was unaffected. Cassidy, who led the 2013 study, is among the review’s authors. An earlier meta-analysis from a separate group, published in 2018, was more mixed. It linked anthocyanins with lower risk of coronary heart disease and heart death but found no relationship between the intake of these compounds and heart attack, stroke or total cardiovascular disease.

Trials, which can test cause, have so far measured blood vessels and blood fats rather than heart attacks. A trial its authors described as the longest-duration such trial to date, run in Norwich and Cambridge with Cassidy among its authors, gave 115 adults with metabolic syndrome, a cluster of risk factors including excess belly fat and high blood sugar, a powder made from freeze-dried blueberries for six months. Eating the equivalent of one daily cup of blueberries improved endothelial function, meaning how well the lining of the arteries lets them widen, while half a cup did nothing measurable. A smaller trial by a different team at the Quadram Institute in Norwich gave 52 adults with high cholesterol anthocyanin capsules for 28 days. It found no effect of isolated anthocyanins on cholesterol or other blood fats.

The 2026 pooled analysis reached the same split across its 65 trials: anthocyanins improved how well arteries widen, but lipids, blood pressure, glucose and insulin resistance were unaffected. Put together, the trials suggest some short-term effect on blood vessels, the cohorts disagree about whether it adds up to fewer heart attacks, and this 28-year cohort found no sign that it does, at least in older women.

What the Women’s Health Study leaves open about berries

Diet was asked about only once, in the early 1990s, and many women will have changed what they ate over 28 years. Errors of that kind tend to blur real effects toward zero, which is one way a modest benefit could be missed. The women were also 45 or older at the start, while the 2013 study recruited women aged 25 to 42, so the two cohorts may be asking slightly different questions. The new study cannot say whether berries eaten earlier in life would matter more.

Because the analysis is observational, a null result argues against a large effect in this group of women more than it proves that berries do nothing for the heart. And an adjustment for lifestyle can overcorrect as well as undercorrect: if some of what made berry eaters healthier ran through the berries themselves, counting it as lifestyle would hide a real effect.

What the result means for anyone eating berries for their heart

Nothing in the new analysis suggests berries are harmful. A benefit too small for even this study to detect remains possible, and the blood-fat link is suggestive, though trials of anthocyanins have not found a change in blood fats. What it weakens is the confident version of the claim, in which a few servings of blueberries a week make a measurable dent in heart attacks.

Heart-health guidance has never rested on a single fruit. The American Heart Association’s 2021 dietary guidance emphasizes eating patterns over individual foods and lists eating plenty and a variety of fruits and vegetables among its recommendations, alongside whole grains, healthy proteins and limits on salt and added sugar. How diet fits into one person’s heart risk is assessed by their doctor.

Over 28 years in 38,088 women, blueberries and their pigments did not go with fewer heart attacks or strokes, though the pigments went with better blood fats.