The results of two recent clinical trials boost the heart-health potential of blueberries — and other colorful berries.

The healthy reputation of blueberries and their colorful cousins rose following the results of studies in rodents and human epidemiological studies. For example, see Berries May Slash Women's Heart Risk and its links to related reports.

Those encouraging findings led to clinical trials that produced similarly positive results: see Blueberries Found to Lower Blood Pressure and Sugar Levels, Strawberries Show Big Heart Benefits, Cranberries Score for Artery Health, and Berry Colors Cut Heart-Attacking Inflammation.

But the trials conducted to date haven’t lasted very long, so the positive findings of a new, six-month trial lend greater weight to the idea that blueberries — and other colorful berries — are very good for heart health.

And the outcomes of two other clinical studies pinpoint the antioxidant pigments in blueberries and other red-blue-purple berries as the secret to their blood-pressure-lowering potential.

Six-month trial sees daily blueberries boosting heart health
The lengthy new clinical trial was conducted by researchers from the Harvard School of Public Health and four British universities, and was led by professor Aedin Cassidy at the University of East Anglia’s Norwich Medical School.

As Dr. Cassidy said, “Previous studies have indicated that people who regularly eat blueberries have a reduced risk of developing conditions including type 2 diabetes and cardiovascular disease. This may be because blueberries are high in naturally occurring compounds called anthocyanins, which are the flavonoids responsible for the red and blue color in fruits.

And he put the goal of their clinical trial this way: “We wanted to find out whether eating blueberries could help people who have already been identified as being at risk of developing these sorts of conditions.”

And instead of testing blueberries in healthy people, the UK-U.S. scientific team wanted to see whether blueberries would bring any benefits to people with metabolic syndrome or MetS (Curtis PJ et al. 2019).

MetS is a set of symptoms, found in one out of three adults in Western countries, that raises their risk for cardiovascular disease and diabetes.

MetS is defined as having at least three out of these five risk factors:

  1. High blood sugar
  2. High blood pressure
  3. High blood triglycerides
  4. Low HDL (“good”) cholesterol
  5. Central obesity (excessive fat in and around the abdomen).

The UK-U.S. team recruited 138 overweight and obese people aged between 50 and 75, who’d been diagnosed with MetS.

They tested the effects of eating 150-gram portions (5.3 ounces) daily — about one cup of blueberries — compared to eating one-half cup (75-grams/2.6 ounces) daily.

The participants were divided into two groups:

  • Test group: Blueberries (freeze-dried)
  • Placebo group: Blueberry substitute with artificial colors and flavors

And the results made blueberries look pretty good. As study co-author Dr. Peter Curtis said, “We found that eating one cup of blueberries per day resulted in sustained improvements in vascular function and arterial stiffness — making enough of a difference to reduce the risk of cardiovascular disease by between 12 and 15 percent.

Coming from the longest clinical trial of its kind, these positive results seem quite significant — especially for people with or at risk of MetS and the outcomes it promotes: cardiovascular disease and/or diabetes.

Unexpectedly, as Dr. Curtis noted, “We found no benefit of a smaller 75 gram (half cup) daily intake of blueberries in this at-risk group.”

But he speculated that amounts less than one cup daily might be enough for healthier people: “It is possible that higher daily intakes may be needed for heart health benefits in obese, at-risk populations, compared with the general population.”

Twin trials see blueberries — and their pigments alone — lowering blood pressure
Medical researchers from King’s College London conducted two other trials — one testing the effects of consuming puréed blueberries, and one testing the effects of consuming just the antioxidant blueberry pigments called anthocyanins.

The second, anthocyanins-only study made sense, because, as the authors of a recent evidence review wrote, “Epidemiological, clinical, and animal studies indicate that blueberry anthocyanins exert protection against cardiovascular complications by acting on multiple targets in the vascular system.”

If so, this implies that people who can’t or don’t want to eat lots of blueberries — or other blue-purple berries — could derive their apparent cardiovascular benefits by taking any of the widely available anthocyanin (or anthocyanin-rich berry extract) supplements.

So, the British team’s twin clinical studies were carefully designed to confirm — or refute — those prior findings (Rodriguez-Mateos A et al. 2019).

Study #1: Puréed blueberries
For this one-month trial, the British team recruited 40 healthy volunteers and divided them into two groups, each assigned to consume a different drink daily:

  • Test group: Drink containing 200g of blueberries
  • Placebo group: Artificially colored substitute drink

The team measured the levels of key chemicals in the volunteers’ blood and urine, as well as their blood pressure and “flow-mediated dilation” (FMD) of the upper arm’s brachial artery.

FMD — which is considered a sensitive marker of cardiovascular disease risk — measures how much that major artery widens when blood flow increases.

And the results were quite encouraging:

  • Positive effects on blood vessel function were detected two hours after consumption of the blueberry drink and lasted for a full month.
  • Over the course of the month, blood pressure among the blueberry group was reduced by an amount (5mmHg) comparable to the reduction typically achieved with blood pressure drugs.

Study #2: Purified blueberry pigments (anthocyanins)
For this study, the UK researchers compared the effects of a puréed blueberry drink with those of drinking purified anthocyanins.

Anthocyanins are the chemicals responsible for the blue, red, pink and purple color of fruits and vegetables such as berries and red grapes.

They also compared the effects of the purified anthocyanins drank with those of “control” drinks containing levels of either fiber, minerals, or vitamins, both of those found in blueberries.

The outcomes confirmed prior evidence from animal studies that has assigned the bulk of blueberries’ cardiovascular benefits to their anthocyanins:

  • The drink containing purified anthocyanins led to improvements in endothelial (artery lining) function. Endothelial cells play key roles in blood clotting and regulating blood pressure.
  • None of the control drinks had a significant effect on FMD at points two and six hours after their consumption.

This was the study authors' conclusion: "Our results identify anthocyanin metabolites [digestive breakdown products] as major mediators of vascular bioactivities of blueberries and changes of cellular gene programs."

As lead researcher Dr. Ana Rodriguez-Mateos said, “Although it is best to eat the whole blueberry to get the full benefit, our study finds that the majority of the effects can be explained by anthocyanins.

And she went on to quantify the benefit: “If the changes we saw in blood vessel function after eating blueberries every day could be sustained for a person’s whole life, it could reduce their risk of developing cardiovascular disease by up to 20%.”


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