The effect is particularly strong for smokers and heavy drinkers, the new study suggests.

Flavonoids are a group of compounds found in plants and fungi which have long been linked with potential health benefits. The new study, which followed 53,048 Danes aged 23 and above, assessed the dietary patterns and health hazards of the participants.

The researchers found that people who regularly consume moderate to high amounts of foods rich in flavonoids were less likely to die from cancer or heart disease. The risk was reduced by 20% — in other words, those with a high flavonoid intake were 20% less likely to die from these diseases.

Lead researcher Dr. Nicola Bondonno said that the results were remarkable, and the protective effect appeared to be strongest for those at high risk of chronic diseases due to cigarette smoking and those who drank more than two standard alcoholic drinks a day. However, it’s important to note that flavonoid consumption does not even come close to fully offsetting the health risks posed by smoking and drinking alcohol.

“These findings are important as they highlight the potential to prevent cancer and heart disease by encouraging the consumption of flavonoid-rich foods, particularly in people at high risk of these chronic diseases,” she said.

“But it’s also important to note 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.”

“We know these kinds of lifestyle changes can be very challenging, so encouraging flavonoid consumption might be a novel way to alleviate the increased risk, while also encouraging people to quit smoking and reduce their alcohol intake.”

So how much flavonoid is enough?

Researchers found that those with an intake of over 500 mg of flavonoids each day had the lowest risk of cancer and heart disease. Furthermore, researchers also highlight the importance to consume a variety of different flavonoids.

“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, 100g of blueberries, and 100g of broccoli would provide a wide range of flavonoid compounds and over 500mg of total flavonoids”.

The exact nature of this effect is unknown, but the results are consistent with previous studies which have shown that a plant-based diet is beneficial to human health and reduces the risk of cancer and cardiovascular disease.

“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,” study authors conclude.

The study has been published in Nature Communications.