Variability of research methods makes establishing reference intake for polyphenols difficult, researchers argue

17-Jun-2019 - Last updated on 17-Jun-2019 at 16:24 GMT

Wine is a well-known, and popular, source of polyphenols. Getty Images / Rawpixel

Though the body of science around polyphenol intake generally supports its health benefits, it is “difficult to establish an evidence-based reference intake for the whole class and subclass of compounds,” researchers argue in a paper.

Published studies so far generally support the idea that a diet rich in polyphenols—a category of chemicals occurring in plants and their products such as tea and wine—may contribute to several health benefits, such as lowered risk of diabetes or cardiovascular disease.

But establishing a recommended amount of polyphenol intake based on these studies is difficult because of the large variability in terms of methods for the evaluation and quantification of polyphenol intake, as well as the diversity of the markers and endpoints considered in the many studies investigating the health benefits of polyphenols.

A team of researchers from various institutions in Italy came to this conclusion after conducting a systematic review of 91 papers on the topic published between January 2008 and December 2018.

“Undoubtedly, polyphenols exert numerous biological activities as reported in a plethora of in vitro and in vivo studies,” they wrote in their paper, published last week in the journal Nutrients.

“However, most of the associations were found for specific polyphenol classes/subclasses as well as markers/endpoints,” they added.

At present, few and conflicting results are available for total polyphenols, they continued. The authors concluded that it is still difficult to establish a reference or prudent intake of total polyphenols as it was 10 years ago, citing a 2008 paper by University of Leeds researchers published in the British Journal of Nutrition that came to a similar conclusion, “even if we found an approximate mean intake of about 900 mg/day.”

Study details

The researchers conducted a systematic review, which is a summarization of existing scientific literature within a specific topic.

They searched for studies published in English in the databases PubMed and EMBASE, looking for keywords such as “polyphenols,” “flavonoids,” “anthocyanins,” and the word “intake.”

Studies included in the review were those that were prospective, cohort and case-control studies analysing/estimating dietary total/classes/individual polyphenol intake; reported the association between dietary total/classes/individual polyphenol intake and endpoints of disease risk and mortality; and published from January 2008 to December 2018.

They did not look at studies on animals or in vitro, or studies where dietary supplements were the main investigated source of polyphenols.

Source: Nutrients
Published online, doi:10.3390/nu11061355
“Systematic Review on Polyphenol Intake and Health Outcomes: Is there Sufficient Evidence to Define a Health-Promoting Polyphenol-Rich Dietary Pattern?”
Authors: Christian del Bo, et al.