BBC News Online: World: Americas

Alarm raised over tobacco substitutes

Scientists in the United States say medicines designed to help people give up smoking may be harmful if used for excessively long periods of time.

In a study on mice, published in the journal Nature Medicine, the researchers found that tobacco substitutes - such as nicotine chewing gum - can stimulate the growth of tumours.

But researchers at Stanford University in the United States have found that nicotine can stimulate the growth of blood vessels, increasing the blood supply to tumours and making them enlarge in size.

Quantities of nicotine that corresponded to the amount of the compound that would be found in the bloodstream of an average smoker were tested on mice.

Faster tumour growth

When cancer cells were implanted in the mice, those mice that received nicotine supplements experienced far more rapid tumour growth.

Nicotine also increased the rate of blood vessel clogging - a condition which can lead to heart attacks and strokes.

The researchers say these effects were seen regardless of whether the nicotine was taken into the body through cigarettes, or through replacement therapies such as chewing gum.

Dr John Cooke, who led the research, says nicotine replacement therapies are a useful tool to help smokers quit smoking. But he says these therapies should be used as directed, and not for long periods of time.