Diets rich in tea, berries and apples could lower blood pressure, according to the first study using objective measures of thousands of UK residents’ eating habits.
Foods and drinks such as tea, apples, grapes, red wine, and cocoa contain flavan-3-ols, which are naturally occurring compounds found in plants known to be associated with lower risk factors for cardiovascular disease.
In contrast to previous large-scale observational research that relied on self-reported food diaries, this study measured flavan-3-ol intake using nutritional biomarkers – characteristics that can be objectively measured in different biological samples to indicate nutritional intake.
The study – published in Scientific Reports and partially funded by the confectionery firm Mars – looked for evidence of two flavan-3-ol biomarkers in urine samples from 25,618 adults in Norfolk and compared it with their blood pressure.
The difference in blood pressure between those with the lowest 10% of flavan-3-ol intake and those with the highest 10% of intake was between 2 and 4mmHg, the researchers found.
According to the study’s lead author, Prof Gunter Kuhnle, a nutritionist at the University of Reading, the association between flavan-3-ol intake and blood pressure remained fairly stable even after adjusting for lifestyle factors such as smoking and physical activity.
But how flavan-3-ol is consumed is crucial, Kuhnle added. “Sometimes I see people saying you should consume chocolate to get healthy flavan-3-ols, but to get to the amount you need to find an effect, you would have to eat so much … you just couldn’t,” he said, noting that eating large amounts of foods high in sugar and fat could wipe out the effects of beneficial flavan-3-ols.
Notably, the effect was more pronounced in participants with hypertension. The improvements were also stronger in women, although Kuhnle said it was unclear why. He added that further study was needed to conclusively prove that higher flavan-3-ol intake directly causes improvements in blood pressure.
Dr Ian Johnson, nutrition researcher at Quadram Institute Bioscience, who was not involved in the study, said: “Although statistically significant, the differences in blood pressure that have been observed are relatively small.”
The researchers compared the biomarker results with seven-day food diaries compiled by the participants. The variability in food composition was immense: for example, one cup of tea is generally considered to contain 180 milligrams of flavan-3-ols, said Kuhnle. “But if you look at actual reported content, it’s anywhere between nought and about 600 milligrams,” he said. “And so the idea that we have sort of standardised food, which we can then use from a food diary or food questionnaire to estimate how much flavan-3-ol most people consume, turned out to be more wishful thinking.”
In the study, the researchers found virtually no uniformity between biomarker-estimated flavan-3-ol intake and the seven-day food diaries. They also found there were no consistent, significant associations between flavan-3-ol biomarker-estimated intake and cardiovascular disease or death.