Can chokeberry be used as an antioxidant?
BACKGROUND
The black chokeberry is a shrub that is native to North America, but was introduced into Europe about a century ago. They have become
popular ornamental plants because of their delicate spring flowers. Most interest has focused on the black chokeberry, although two closely related shrubs produce red or purple berries.
Although chokeberries are edible (and look a lot like blackcurrants), they are so bitter people often choke on them – hence their name. In spite of this, the berries are used to make jams, juices and various aronia food products.
This name comes from the plant's scientific name: Aronia melanocarpa.Such products have been heavily marketed in recent years because the berries are very high in antioxidants. In addition, the plant is pest-resistant and easy to cultivate, increasing its value as a commercial crop.
EVIDENCE FROM STUDIES
Recent interest in antioxidants has led to a search for new natural sources. Normal metabolism in the body produces several types of byproducts which cause oxidation. This occurs throughout the body, but when oxidant levels get too high, damage can occur.
Such oxidative stress has been implicated in the development of various chronic illnesses, including heart disease, some cancers, and inflammatory diseases. Oxidative stress has become more prevalent as modern eating habits have led people to less fresh fruit and vegetables.
Plants produce a variety of compounds called phenolics, which have varying levels of antioxidant activity. Chokeberries contain compounds called anthocyanins which give the black colour to their berries.
Black chokeberries contain some of the highest levels of anthocyanins found in any plant. Due to these and other antioxidants in black chokeberries, they have one of the highest levels of antioxidant strength yet recorded.
Claims have also been made that black chokeberries prevent heart disease, aid digestion, combat infections, enhance memory and prevent cancer. Support for such claims usually relies on studies carried out in cells and tissues. The link between such laboratory studies and clinical effects is unclear.
A systematic review of clinical trials with black chokeberry products was published at the end of 2010. The review located 13 studies carried out in patients with a wide variety of conditions, all of which were related to oxidative stress. Various outcomes were measured to determine whether beneficial effects occurred.
However, each study made several measurements without determining in advance if one was the primary focus of the study. Such an approach is problematic because it increases the likelihood of finding positive results just by chance.
Accordingly, every study found at least one positive result, although most outcomes did not show improvements. Almost half of the studies did not have a control group, and most lasted only one or two months. For this reason, the systematic review concluded that while the evidence is promising, its quality is very poor.
PROBLEMATIC ASPECTS
Studies in animals and humans have not reported any adverse effects. However, high levels of anthocyanins can interfere with the actions of other medicines. Anthocyanins also combine readily with iron and could lead to anaemia if taken in large quantities. These concerns have not been studied specifically with black chokeberry.
RECOMMENDATIONS
Black chokeberries are a very good source of antioxidants and some other nutrients. While this makes them a nutritious fruit to add to the diet, their bitterness makes them difficult to consume. Alternative ways to formulate the fruit are being developed. For example, seven of the clinical trials used a Polish product called Aronox, which contains a standardised amount of black chokeberry anthocyanins in tablet form. The other trials used black chokeberry juices.
Overall, the research results are promising, showing that black chokeberries are a good source of antioxidants and reduce oxidative stress. Evidence is not currently available that black chokeberries prevent or treat any specific condition.
Dónal O’Mathúna has a PhD in pharmacy, researching herbal remedies, and an MA in bioethics, and is a senior lecturer in the School of Nursing, Dublin City University