Widely believed to arouse passion, the spicy sweet drink from the New World -- 'chocolatl' -- was considered by some to be the food of the devil. In 1624, the religious leader Johan Franciscus Rauch exhorted monks not to drink it. But while condemnation rang out from the pulpits, European royalty sent each other betrothal gifts of chocolate.

Initially restricted to the privileged, wealthy members of society, chocolate is now inexpensive and widely available. But it still has overtones of luxury, indulgence and decadence. Indeed chocolate is so much associated with sensual pleasure that even cosmetics manufacturers now lure us with chocolate bath oils and massage bars that smell tantalisingly edible. And it is still the focus of heated debate.

This notorious delicacy is derived from the beans of a tropical evergreen tree Theobroma cacao, a botanical name meaning 'food of the gods'. Originating from the forests of central and South America, Theobroma cacao trees were planted by early civilisations such as the Mayans nearly two-and-a-half millennia ago. Many cultures followed suit, harvesting the brilliantly coloured cocoa-bean pods.

The beans were roasted, ground, and then mixed with water, grains and spices such as chilli, into a drink for the elite. The conquistador Hernando Cortez, who destroyed the Aztec civilisation in the sixteenth century, reported that chocolatl improved a person's resistance to disease and their stamina. The Aztec emperor, Montezuma (whose name has become synonymous with gourmet chocolates) was believed to consume over 50 goblets of it before visiting his harem.

Montezuma was not alone in his passion for chocolate. Variations on the traditional bitter, spicy beverage are still drunk in Southern and Central America today, although now chocolate is most often consumed as the sweet solid confectionery we all know and love. In fact, The Economist reported that last year the British alone munched a staggering average of 9.5 kilograms of chocolate each -- the equivalent of 38 Easter eggs.

Why? Well, one intriguing clue comes from studies carried out by Alan Hirsch, the director of Chicago's Taste and Smell Research Foundation. He has shown that the scent of chocolate causes a slight increase in penile blood flow. Why or how is unclear.

Chocolate has long been associated with romance and this may be due to one of its ingredients -- 'phenethylamine' -- controversially dubbed the 'love chemical'. The brain releases phenethylamine when a person is sexually aroused; it increases both heart rate and blood pressure. So is chocolate an aphrodisiac?

"Chocolate has no pharmacological effects," says Adam Drewnowski, the Director of the Nutritional Sciences Program at the University of Washington. In his opinion, the 'love chemical' is an invention of the confectionery industry. Phenethylamine in chocolate is broken down in the digestive system. So it cannot affect the brain, he argues.

Instead, Drewnowski explains, chocolate has a high calorific content that quickly satisfies the appetite. Chocolate also stimulates the brain to release endorphins that act on the central nervous system. Endorphins are natural painkillers and also appear to affect behaviour. Elevated levels boost our sense of well being -- hence the chocolate 'high'.

But does the feel-good surge we get after eating chocolate mean that it is good for us? Yes, Cesar Fraga, of the University of Buenos Aires, and his colleagues told the American Association of the Advancement of Science's annual meeting in Washington earlier this year. Adults who eat chocolate, Fraga's team found, have increased levels of anti-oxidants in their blood. The researchers also suggest that the cells of chocolate consumers are less vulnerable to 'free radical' damage. This could be due to flavonoids -- antioxidants found in many plant products, including cocoa.

Free radicals are unstable atoms or molecules that lack an electron. They 'steal' an electron from a neighbour, triggering a damaging chain reaction in surrounding biochemical compounds. The heart and vascular system are particularly prone to the havoc that these reactions can wreak: free radicals cause clots and fatty deposits in the bloodstream and harden the cellular lining of arteries and veins, possibly leading to heart disease and strokes.

But clearly, chocolate is not a 'health food'. Tissa Kappagoda from the University of California at Davis, a cardiologist who has studied flavonoids in grapes and cocoa is wary about studies that appear to validate the benefits of eating chocolate. He describes flavonoids as "potentially beneficial" but is concerned about the impact of promoting chocolate. After all, a one-hundred gram bar can contain about 50 grams of sugar (12 teaspoons) and up to 37 grams of saturated fat.

Unfortunately, as Alan Hirsch points out, "forty percent of women and fifteen percent of men crave chocolate despite knowing that it has detrimental health effects". Many people cheerfully describe themselves as 'chocoholics'. Does this mean chocolate is addictive like cocaine, alcohol or tobacco?

"I don't think that chocolate produces anything comparable to these drugs. But, under certain circumstances, chocolate may stimulate craving," says Daniele Piomelli, from the University of California, who has carried out extensive research into the pharmacology of chocolate. It is likely, he thinks, that there is a sensory component involved in the craving for chocolate and he points out that "the smell and taste of a substance can contribute to make it desirable, just as can the settings in which it is consumed".