Coca has been central to many South American cultures for millennia, and Bolivia is one of the continent"s biggest producers, with hundreds of square kilometres devoted to the crop, two-thirds of which are in the Yungas. High in vitamins and minerals, the leaves act as a mild stimulant and help to offset altitude sickness; stave off hunger, thirst and tiredness; aid digestion and even suppress pain. For as long as 8,000 years, they have been used in religious ceremonies, and as a medicine, currency and social lubricant.