ONCE it was a simple question: tea or coffee? Now, after a scientific breakthrough, that choice will become rather less straightforward.
Researchers have found that a rare type of tea made from the coffee plant is healthier than both the other drinks.
Coffee leaf tea contains high levels of compounds credited with lowering the risk of heart disease and diabetes.
The leaves are also found to contain more antioxidants than normal tea, which is already renowned for its healthy properties, and high levels of a natural chemical found in mangoes known to combat inflammation.
The researchers believe the leaves of the Coffea genus have been overlooked because of the high value placed on its seeds, the coffee beans, which contain far fewer beneficial compounds.
Researchers from the Royal Botanic Gardens in Kew, London, and the joint research unit for Crop Diversity, Adaptation and Development in Montpellier, France, believe coffee leaves can provide a healthy drink to rival coffee and traditional green or black tea. The drink, which has low levels of caffeine, has an earthy taste neither as bitter as tea nor as strong as coffee.
A coffee expert and botanist at Kew who conducted the research, Aaron Davies, said coffee leaf tea was popular in places such as Ethiopia and South Sudan, and there was even an attempt to sell it in Britain in the 1800s.
Dr Davies has found samples of coffee leaf tea in the Kew collections that date back nearly 100 years, from when coffee producers in Sumatra and Java tried to popularise it in Britain and Australia.
''In 1851, people were touting it as the next tea and there were all these reports about its qualities,'' he said. It was said to give immediate relief from hunger and fatigue, and ''clear the brain of its cobwebs''. It was also said to be refreshing, although some found it undrinkable.
Tests on 23 species of coffee by Dr Davies and Claudine Campa from Montpellier have found that the leaves of seven have high levels of mangiferin, a chemical found in mangoes and believed to have anti-inflammatory effects, reduce the risk of diabetes, lower blood cholesterol and protect neurons in the brain.
The results, published in the journal Annals of Botany, show that Coffea arabica leaves have higher levels of antioxidants, which is thought to be beneficial in combating heart disease, diabetes and even cancer, than tea or coffee.
Coffee leaf tea is not yet widely available, but is sold by some health food shops. A master tea taster, Alex Probyn, who runs a blending business and tried the drink in Ethiopia, tested a sample from the United States.
''The coffee leaves have quite a pungent and greenish character. They are bitter but not unpleasant,'' he said. ''The sample … has a slightly menthol and eucalyptus taste that makes me think something has been added to it to soften the bitterness.
''If I could find a source then I would use coffee leaves in my own blends as I think it offers something a little bit different.
''The difficulty may be that coffee growers will want the leaves to stay on their plants so they can produce good beans.''
Coffee beans are the world's second most valuable commodity after crude oil, with almost eight million tonnes produced a year in an industry worth more than $66 billion.