A study probes the link between polyphenol consumption and mortality.
A considerable amount of research has focused on the role of nutrition in disease risk and mortality.
Despite growing interest, it is a notoriously difficult topic to study for a range of reasons, and drawing reliable conclusions about how food impacts specific health outcomes is challenging.
Although it is obvious that food is vital to our survival, delving deeper into the details of how single compounds impact disease and mortality in humans is difficult.
With that said, researchers have now firmly and scientifically established that eating more fruit and vegetables is associated with reduced cardiovascular and overall mortality risk.
However, exactly how fruits and vegetables protect health is less well known; although a wide array of nutrients are likely involved, many researchers believe that flavonoids play a significant part.
The flavonoid family
Flavonoids are a class of chemicals called polyphenols. They are present in a range of natural foods, including fruits, vegetables, dark chocolate, red wine, and tea.
These compounds have six subclasses:flavonols flavan-3-ols flavanones flavones anthocyanins isoflavones
Each of these has the potential to impact the body in different ways and to different degrees.
Recently, a group of scientists from Edith Cowan University in Australia set out to investigate if these compounds actually can extend life and protect health.
The paper, which now appears in the journal Nature Communications, outlines their findings.
The authors write that their primary aim was to "investigate the association of total flavonoid and flavonoid subclass intakes with all cause, [cardiovascular disease]-related, and cancer-related mortality."
The researchers also wanted to see how lifestyle factors such as drinking alcohol and smoking tobacco affected the benefits derived from flavonoids.
Earlier studies investigating flavonoids produced interesting results. In short-term studies, they appear to boost certain markers of cardiovascular health. Other papers have described a potential anticancer role for flavonoids.
Although earlier research has hinted at benefits, there are significant gaps. As the authors of the new study explain:
"Evidence from observational studies is incomplete; studies on cancer mortality are scarce, and additional research is necessary to establish the specific role of flavonoid subclasses and to determine the dose of total and specific flavonoids required to achieve maximum benefit."
To investigate, the scientists took data from the Danish Diet, Cancer, and Health cohort. In total, 56,048 adults took part. During the 23-year followup, 14,083 of the participants died.
After controlling for a range of factors, the authors conclude:
"[W]e provide evidence that an achievable dietary intake of total and individual flavonoid subclasses is associated with a lower risk of all cause, [cardiovascular disease]-related, and cancer-related mortality."
Specifically, they found that those who consumed around 500 milligrams (mg) of flavonoids every day had the lowest risk of cancer- or cardiovascular disease-related deaths. Above the 500 mg threshold, there was no additional benefit.
The scientists also analyzed the impact of each of the six types of flavonoid. They found the same effect across the board.
500 mg each day
To put the 500 mg threshold into perspective, lead researcher Dr. Nicola Bondonno provides an actionable example:
"It's important to consume a variety of different flavonoid compounds found in different plant based food and drink. This is easily achievable through the diet: one cup of tea, one apple, one orange, 100 grams of blueberries, and 100 grams of broccoli would provide a wide range of flavonoid compounds and over 500 mg of total flavonoids."
The researchers found that the benefits of flavonoids were particularly pronounced in participants who currently smoked and who consumed more than two alcoholic beverages each day. These participants saw the greatest benefits.
However, Dr. Bondonno makes an important point, explaining that "flavonoid consumption does not counteract all of the increased risk of death caused by smoking and high alcohol consumption. By far the best thing to do for your health is to quit smoking and cut down on alcohol."
Exactly how flavonoids might reduce the risk of disease is unclear. However, some scientists believe that their anti-inflammatory qualities might be important.
Alcohol and tobacco both increase levels of inflammation and damage blood vessels. However, as Dr. Bondonno explains, "Flavonoids have been shown to be anti-inflammatory and improve blood vessel function, which may explain why they are associated with a lower risk of death from heart disease and cancer."
Strengths and limitations
This study has significant strengths — not least the large number of participants and the long follow-up duration. The scientists also captured a wide range of characteristics, lifestyle factors, and other relevant information to help refine their analysis and reduce statistical noise.
However, there are always limitations. For instance, the study was observational, which means that it is not possible to prove conclusively that flavonoids cause the decrease in mortality and disease risk.
For instance, as the authors explain, there is a possibility that flavonoids are "a marker of other unobserved and potentially protective dietary factors."
Importantly, the study only captured dietary information at the start of the study; there is every chance that the participants' diets changed significantly over the following 2 decades.
The authors also note that their sample group was predominantly white, so the relationship between flavonoids and health outcomes may be different in other populations.
In conclusion, this study adds weight to the idea that flavonoids might protect health. However, as ever, scientists will need to carry out more research.
In the meantime, consuming increased quantities of fruits and vegetables will do no harm.