According to the researchers, cigarette tobacco additives, including plum juice, maple syrup, honey and fig juice, increase levels of toxic chemicals, including formaldehyde, produced when smokers light up. The report says sugars also make cigarettes more appealing, especially for young people.

"The addition of sugars to tobacco can enhance tobacco use in at least two ways . . . neutralisation of the harsh taste of cigarette smoke and generation of acetaldehyde, which increases the addictive effect of nicotine. Since consumer acceptance of tobacco smoke is, amongst others, proportional to the sugar level in tobacco, manufacturers select natural high-sugar tobaccos or add sugars during tobacco manufacturing."

It says that while sugars are recognised as being safe when used in food products, that doesn't mean they are safe as a tobacco additive.

According to the report by scientists from the National Institute for Public Health and the Environment in the Netherlands, the natural sugar content of tobacco is highly variable, but primarily depends on the method of curing, with flue-cured, like Virginia tobacco, and suncured tobaccos containing higher sugar levels.

As well as the natural sugars, others are added:

"During the manufacturing process of a tobacco product, sugars and sweeteners are intentionally added to tobacco. Sugars used as cigarette additive include glucose, fructose, invert sugar (glucose/fructose mixture), and sucrose.

"In addition, many tobacco additives contain high amounts of sugars . . . fruit juices, honeys, molasses extracts, corn and maple syrups, and caramel, " say the scientists, whose study appears in the journal, Food and Chemical Toxicology. They say tobacco companies claim that ingredients are added to tobacco products to aid the production process.

"However, sugars also promote tobacco smoking, because they generate acids that neutralise the harsh taste and throat impact of smoke. Moreover, the sweet taste and the agreeable smell of caramelised sugar are appreciated in particular by adolescent smokers."

On the toxic effects of burning sugars, they say, "High-sugar tobaccos yield elevated levels of toxic components in mainstream smoke. Many toxic (including carcinogenic) smoke compounds are generated from sugars. In particular, sugars increase the level of formaldehyde, acetaldehyde, acetone, acrolein, and 2furfural in tobacco smoke. It is concluded that sugars in tobacco significantly contribute to the adverse health effects of tobacco smoking."

Chris Proctor of British American Tobacco, said, "The style of cigarettes sold in the UK are overwhelmingly Virginia-style cigarettes. They typically do not have sugar added to them. Yet there seems to be no difference between these and the American-blended cigarettes sold in most parts of Europe, which typically have added sugar. . .

"We do not believe, on the basis of existing science, that cigarettes where sugar has been added are any more dangerous or any more attractive to young people than those that have no sugar added."