Anthocyanins are water soluble pigments found in many plants. These pigments have several functions in the plant, and they are also of nutritional interest, because they have been linked with nutritional benefits such as cancer prevention. People eat anthocyanins every day, and many people have a diet rich in these pigments.
Depending on pH, anthocyanins can be red, violet, or blue. The bright red color of an apple is due to the presence of anthocyanins, as is the rich blue of a blueberry. These pigments can be found in fruits, stems, and leaves, and their levels may fluctuate. New plant growth, for example, is often tinged red with anthocyanin, with the pigment flushing out as the plant develops and the growth matures.
In plants, one of the key roles of anthocyanins is as a form of sunblock. These dark pigments protect plants from sun damage, and decrease the risk that a plant will be burned or wilted by hot sun. Anthocyanins also act to attract pollinators by acting as bright flags which will be easy for birds, bees, and other organisms to see, which is why many flowers are bright red in color. The antioxidant qualities of anthocyanin pigments also appear to be important to plant health, as oxidation can hurt plants just like it hurts other organisms.
These compounds are among a large family of compounds known as flavonoids. Flavonoids have been fingered in a number of nutritional studies as potential preventative nutrients which could keep people healthier, and some appear to be able to shrink tumors and treat some diseases. Anthocyanins are no exception to the rule, with these pigments having a number of benefits, primarily in their role as antioxidants. Anthocyanin pigments are one reason why fruit is so healthy, and why health claims are made about wines and fruit juices.
Like many of the compounds found in plants, anthocyanins are very complex, and their activities in the body and in plants may be the result of interactions between several different chemicals, which makes it difficult to isolate specific compounds for study. This is one reason why fresh whole fruit is sometimes viewed as nutritionally superior to extracts, juices, and dried fruit products, because whole fruit contains a distinctive balance of nutrients which is difficult to replicate, and the actions of these nutrients are not always known, despite the best efforts of researchers who would like to pin down the health benefits of fruit.