Smoking linked to multiple sclerosis, says study

By STEVE CONNOR

Smokers are at greater risk of developing multiple sclerosis, says a study that has established the first clear link between smoking and the nerve disease.

Scientists found that smokers in their 40s were almost twice as likely as non-smokers to develop MS in later life, with male smokers having 2.7 times the risk.

The study examined 87 multiple sclerosis patients in a sample of 22,312 people between the ages of 40 and 47 living in the Norwegian county of Hordaland.

The aim was to identify the environmental factors that increase the chances of developing MS.

Professor Trond Riise, of the University of Bergen, said the findings meant the chances of developing multiple sclerosis rose from a typical risk of one in 1000 for the general population to about two in 1000 if a person had smoked in the past.

"This is the first time that smoking has been established as a risk factor, but smoking is not a necessary precondition because there are some multiple sclerosis patients who have never smoked," Professor Riise said.

A study two years ago of women nurses in America discovered a slight increase in the risk of multiple sclerosis among those who smoked but this earlier research, with two prospective studies in Britain which also indicated a possible link, was considered to be inconclusive.

Although the latest research in Norway did not shed any light on the causes of multiple sclerosis, or the precise mechanism whereby smoking could increase the risk, the findings were nevertheless clearly linked with cigarettes, Professor Riise said.

"This is one more reason for young people to avoid smoking."

Multiple sclerosis is an auto-immune disease brought about when the body's immune defences attack the fatty sheath of material that normally insulates and protects the nerve cells of the brain and spinal cord.

The causes of the disease are believed to be a combination of genetic factors and environmental influences, such as viral infections that damage the central nervous system.

Professor Riise said the link with cigarettes might be because smokers were in general more prone to viral infections of the throat.

It is also known that smoking weakens the important tissue barrier between the blood and the brain, perhaps increasing the risk of viruses affecting the central nervous system.

"There are several plausible mechanisms that could explain why smokers are at significantly higher risk than non-smokers," he said.

"Smoking is known, for instance, to interfere generally with the immune system.

"Or it could be the direct toxic effects of nicotine."


- INDEPENDENT

MS Society of Auckland