The study, supported by the US Highbush Blueberry Council (USHBC), noted a number of improvements in vascular function, lipid status, and underlying nitric oxide (NO) bioactivity following one cup of blueberries per day.
With observations that represent a 12–15% reduction in CVD risk, the team from University of East Anglia (UEA) and Harvard identify blueberries as a key component in a future dietary strategy.
“Previous studies have indicated that people who regularly eat blueberries have a reduced risk of developing conditions including type 2 diabetes and cardiovascular disease,” said study lead researcher professor Aedín Cassidy from UEA's Norwich medical school.
“This may be because blueberries are high in naturally occurring compounds called anthocyanins, which are the flavonoids responsible for the red and blue colour in fruits.
"We wanted to find out whether eating blueberries could help people who have already been identified as being at risk of developing these sort of conditions."
Blueberries’ main bioactive constituents that include anthocyanins are likely to be candidates behind the improvements to CV health and the components of Metabolic Syndrome (MetS).
Notably, blueberry intake (ranging from less than 1 to 3 portions per week) are linked to these benefits, countered by a limited number of randomised controlled trial (RCT) evidence.
While single-portion studies and continuous feeding over 6–8 weeks have pointed to vascular function improvements, not all studies report these positive vascular outcomes.
In this study, the team enrolled 138 overweight and obese people, aged between 50 and 75, with Metabolic Syndrome in a six-month study that was the longest trial of its kind.
These people were randomly assigned to one of three treatment groups, consisting of 150 and 75 grams (g) of freeze-dried form blueberries per day
Treatment for the placebo group consisted of a purple-coloured alternative made of artificial colours and flavourings.
Researchers found that a daily intake of one cup improved endothelial function, systemic arterial stiffness and attenuated cyclic guanosine monophosphate concentrations.
"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%,” said co lead study author, Dr Peter Curtis, research Fellow/trials co-ordinator at the University’s medical school.
"Unexpectedly, we found no benefit of a smaller 75g (half cup) daily intake of blueberries in this at-risk group.
“It is possible that higher daily intakes may be needed for heart health benefits in obese, at-risk populations, compared with the general population."
Half a cup insufficient
The team added that a lack of any significant results here warranted further speculation with half-a-cup per day for six months might be “insufficient to provide chronic benefits in an obese, at-risk population”.
Referring to previous short duration studies that provided approximately 335–742 milligrams (mg) anthocyanins per day, the team noted that a daily half cup of blueberries provided lower anthocyanin intakes of 182mg per day.
This intake resulted in significantly lower concentrations of total serum metabolites than the one-cup group.
“We reason, based on animal data showing that anthocyanin intake profoundly affects gut microbial community structure.
“This leads to improved biomarkers of cardiometabolic risk, that the lower serum metabolite concentrations and metabolite profile variability (identified in urine) may, in part, be responsible for a lack of an intervention effect in our half-cup group.”
Source: The American Journal of Clinical Nutrition
Published online: DOI: 10.1093/ajcn/nqy380
“Blueberries improve biomarkers of cardiometabolic function in participants with metabolic syndrome—results from a 6-month, double-blind, randomized controlled trial.”
Authors: Peter Curtis et al.