The findings support past research that shows the antioxidant-packed berries lower cholesterol and improve how the arteries function.
No one has to tell you that blueberries are good for you. Now, a new study adds to the mounting evidence that the fruit may improve heart health.
The new research, published in the June 2019 issue of The American Journal of Clinical Nutrition, found that eating the equivalent of 1 cup of blueberries per day for six months improved arterial function and cholesterol levels in adults with metabolic syndrome. The U.S. Highbush Blueberry Council, which represents blueberry farmers, processors, and importers, funded this study.
How Researchers Studied the Heart Benefits of Blueberries
In the study, participants were overweight and obese adults, age 50 and older, and had metabolic syndrome, which is a cluster of symptoms that includes high blood pressure, high triglycerides, and high blood sugar, and raises the risk of developing type 2 diabetes and heart disease. Researchers randomly assigned 138 total adults to one of three groups: one that consumed the equivalent of 1 cup of blueberries per day in the form of a freeze-dried powder, one that ate ½ cup of whole blueberries per day, and a placebo group, who didn’t eat any blueberries or blueberry product. The placebo group consumed a powder that tasted identical to the first group’s blueberry powder. The participants then got blood tests so study authors could assess their fasting glucose, cholesterol, and triglyceride levels, as well as their blood pressure before the study and six months later.
The results were good news for blueberry lovers. “Our test showed that 1 cup of blueberries per day for six months generally improved the vascular environment by increasing the responsiveness of arteries to [produce] changes in blood flow, improving the flexibility of systemic arteries, and at the same time, increasing the concentration of good lipids and lipoproteins, like HDL, which removes potentially harmful fats form the bloodstream and arteries,” says Peter Curtis, PhD, lead study author and a senior research fellow in the department of nutrition and preventative medicine in Norwich Medical School at the University of East Anglia in England.
Why Scientists Believe That Blueberries Are a Boon for Your Heart
Why the boost to ticker health? Blueberries are packed with anthocyanin flavonoids (which have antioxidant properties) and fiber, says Dr. Curtis. “We showed that blueberries improved the concentration of lipids and lipoproteins, which are thought to scavenge harmful fats from the system, including the blood vessel walls; it’s likely this contributed to an improved cardiovascular performance,” he says. The berries may also help relax tissue that surrounds arteries, another boon for your heart. Interestingly enough, a ½-cup portion wasn’t effective.
The findings aren’t exactly surprising. Studies — even those from a decade ago — have already indicated that a variety of berries may be cardioprotective. For instance, an article published in August 2018 in the Journal of Agricultural and Food Chemistry noted that blueberries may help protect against atherosclerosis — or clogged arteries — by lowering inflammation, reducing cholesterol, combatting oxidative stress (or free-radical damage caused by environmental, dietary, and lifestyle factors, per past research), and improving gut health, among other mechanisms. When atherosclerosis affects the arteries that are connected to the heart, coronary artery disease happens, according to the Mayo Clinic.
Berries are also a main component of the MIND diet, an eating pattern that’s been found to slow cognitive aging and protect against Alzheimer’s disease, per an article published in October 2015 in the Journal of the Academy of Nutrition and Dietetics. And blueberries specifically have been declared “one of the best functional fruits” for preventing chronic disease, according to a review published in September 2018 in the International Journal of Molecular Sciences.
“I think we should all include blueberries and other fruits in our diets on a regular basis,” says Jill Weisenberger, RDN, CDE, author of Prediabetes: A Complete Guide, who is based in Newport News, Virginia.“ Berry intake has been linked in other research to reduced risk of type 2 diabetes, so they are on my list of foods to include to prevent type 2,” she says. But don’t make the mistake of adding blueberries to an otherwise not-so-healthy diet and expecting them to do the heavy lifting — they should be included in an all-around healthy diet. “More plants, in general, helps to prevent chronic disease,” she adds.
Does the New Blueberry Study Have Any Limitations or Caveats?
The study was double-blind and placebo-controlled, which is considered the gold standard. Nutrition is notoriously difficult to study, as many trials rely on self-reported dietary intakes and extrapolating association from there. (If you have trouble recalling what you ate for lunch last Tuesday, you can see why this method is often criticized.) But this study was different in that it controlled blueberry intake and gave “prescriptive” guidance on other foods and lifestyle habits that could impact results, says Curtis. “We are confident the changes observed are attributable to the intervention we gave,” he adds. The main limitation was that the study subjects were mainly white males, so additional trials are needed to see if the results apply to women and a more ethnically diverse population.
The other caveat, as mentioned before, is the funding source. In their study, the authors write that the U.S. Highbush Blueberry Council had no active role in organizing, collecting data, or making conclusions. While it’s important to know who’s behind the funding, says Weisenberger, “Industry-funded research cannot be discounted simply because they have a stake in the game. I believe that industry not only has a right to do their own research, but they also have an obligation. Nutrition is a science, so we need quality research.” Consider that, in general, without industry research, there may not be much research into a particular food. Nevertheless, there’s always potential for bias when industry is involved, other experts — such as Marion Nestle, PhD, the Paulette Goddard Professor and professor emerita of nutrition, food studies, and public health at New York University in New York City — famously argue.
So, should you go crazy on blueberries? In the future, Curtis says we also need more studies looking a healthy population. “It’s possible that those without metabolic syndrome would respond more favorably to a ½-cup portion,” he says. Until that happens, continue to eat blueberries if you love them.