Flavonoids are a group of polyphenolic phytonutrients that are widespread amongst the plant kingdom. The flavonoid class is made up of a number of subclasses including flavones, flavanones, flavan-3-ols, anthocyanins, proanthocyanidins and flavonols. Flavonoids are responsible for many of the red, blue and purple colours in plants, including in petals, fruits and vegetables. The exact role of flavonoids in plants is not known but it suspected they have a number of roles including antioxidant protection. Flavonoids are bioavailable in humans and once absorbed accumulate in tissues. Evidence from cell culture, animal and human studies suggests that flavonoid may have an antioxidant and gene regulatory function in humans, and this may explain the health effects seen with regular consumption of flavonoid containing foods. For example, flavonoid may have anti-inflammatory, antioxidant, immune stimulatory, antihypertensive and hepatoprotective effects.
The association between flavonoids and health have been reported in numerous epidemiological studies. One of the first to report the beneficial effects was the Zutphen Elderly study that ran through the 1980’s and 1990’s, and it was this study that reported an inverse association between flavonoids and cancer risk. However, since this time a number of other studies have confirmed these findings. For example, in a study published in 2014, researchers used food intake and medical health data taken from the Nurses’ Health Study pertaining to middle aged women and used it to assess the association between flavonoid intake and health1. The results of the study showed that those women with the highest intake of flavonoids had a greater chance of obtaining health during ageing, compared to those with the lowest intake of flavonoids. Flavones, flavanones, anthocyanins and flavonols all showed protective effects against age-related disease. In terms of food, oranges, berries, onions and apples all showed protective effects from disease.