Eating a cup of blueberries a day decreases risk of heart disease by up to 15%, even among those already at risk, finds a new study published in the American Journal of Clinical Nutrition.
These findings add to those from several previous studies showing both heart and brain-health benefits from eating blueberries, along with a variety of other dark-colored berries rich in compounds called flavonoids that give the fruits their color (especially a type called anthocyanins, thought to be potent antioxidants). The findings do, however, have some limitations, which we’ll discuss in a minute.
Researchers were interested in the effects of eating blueberries on Metabolic Syndrome, the condition defined as a composite of risk factors including high blood pressure, high blood sugar, low levels of HDL cholesterol, high levels of triglycerides, and excess body fat around the waist.
When those factors appear together, risk of developing heart disease and diabetes escalates. Some estimates suggest that as many as 35% of U.S. adults have Metabolic Syndrome, and nearly 50% of adults over 60. The consequences of having the condition are potentially severe, with an estimated risk of developing heart disease between two to four times higher than the general population.
Researchers evaluated the effects of eating either a cup (150 grams) or half a cup of freeze-dried blueberries a day for six months in nearly 140 overweight adults diagnosed with Metabolic Syndrome. A control group ate a placebo designed to mimic the color and flavor of blueberries.
The researchers reported that eating a cup of the berries a day “resulted in sustained improvements in vascular function and arterial stiffness,” enough to reduce risk of cardiovascular disease between 12-15%.
Eating half a cup (75 grams) didn’t produce the same results, suggesting that higher risk individuals may need the extra-high flavonoid boost to make a difference.
Insulin resistance and blood pressure weren’t affected by eating berries in either group.
The study has a couple of limitations worth noting, including its relatively small size (it could use replication with a larger group), and most importantly that it was partly funded by an organization called the US Highbush Blueberry Council. According to the group’s website, it’s “an agriculture promotion group made up of blueberry farmers, processors and importers in North and South America, who work together to research, innovate and promote the fruits of their labors as well as the growth and well-being of the entire blueberry industry.” The group “is funded by its members, with independent oversight from the USDA,” says the site
Skepticism is warranted anytime a group with a vested interest in a study’s outcome helps pay for it. Positive research findings like these generate news and social media coverage, which can of course benefit the industry supporting the item in question.
Having said that, it’s not like this is the first study to link blueberries and other berries with health benefits. Many already have. The difference with this study was its focus on Metabolic Syndrome and high-risk participants. In addition, this was a double-blind, placebo-controlled study, a more rigorous design than the typical observational research we often see in this space, and six months is a significant amount of time to evaluate results — also a plus.
When viewed with the backdrop of previous research, these findings are another worthwhile data point to consider when thinking through diet choices.
(The study was published in The American Journal of Clinical Nutrition)