People with multiple sclerosis who smoke cigarettes may be doing more harm than they realize, warns a new study from Harvard University.1
Cigarette Caveat
Funded by a grant from the National Multiple Sclerosis Society, the research suggests that cigarette smoking may contribute to the progression of MS. This implies that quitting smoking could potentially reverse or delay worsening of the disease, the researchers speculate. It's the first time that a modifiable risk factor for MS progression has been identified, they say, enabling a new strategy for people with the disease to control the neurological damage that occurs with it.
"The findings are interesting because no modifiable risk factors for the progression of MS are known," said Miguel Hernan, MD, DrPH, in the department of Epidemiology at the Harvard School of Public Health, and the study's chief researcher. "This is the first prospective study that identified a potential intervention (quitting smoking) for reducing the risk of progression of MS."
The study's findings appear in the March 9 issue of the journal Brain.1
Possible Link to MS Advancement Uncovered
To reach their conclusions, Hernan and his associates analyzed information gathered from more than 2,000 medical records maintained in a large database in London, England. The researchers identified 179 British patients who were originally diagnosed with relapsing MS, the most common form of the disease in which episodes of acute worsening occur followed by unpredictable periods of partial or complete recovery.2 Using statistical analysis, Hernan's group determined that of those in that group, current or past smokers faced more than three-and-a-half times the risk of developing secondary-progressive MS, a later stage of the disease marked by a steady deterioration of the central nervous system.
The progression of MS also occurred more rapidly in current or past smokers identified in the study, though the reason wasn't stated.
The findings, Hernan and his team pointed out, mirror those of earlier research that suggested cigarette smoking increases the odds that someone will be diagnosed with an early stage of MS.3,4 In one study,4 doctors did not find a cause-and-effect relationship between smoking and MS risk, but noted a strong association between the two.
Theories Postulated
If smoking is a major cause of disease progression in MS, the reasons aren't known just yet. One possible theory is that nitrous oxide—a chemical found in cigarette smoke—may play a significant role in speeding up the deterioration of nerve fibers in the brain and spinal cord.
Another theory is that the chemicals in the smoke might damage the cells that create myelin, or may even predispose smokers to autoimmune responses. Those theories, however, still need to be investigated.
When MS strikes, it's believed that an immune system attack targets myelin, a fatty sheath surrounding nerve fibers in the brain and spinal cord. When myelin is destroyed, it leaves the sensitive fibers unprotected and unable to communicate with each other, leading to the symptoms found in the disease.2
"Our findings raise a number of other questions that future research needs to address," Hernan stated. Experts want to know if greater levels of exposure to cigarette smoke directly increase the risk of MS progression, how long the effect of tobacco exposure may last in this context, and whether exposure to second-hand cigarette smoke also poses a possible danger, he said.
1. Hernan MA, Jick SS, Logroscino G, Olek MJ, Ascherio A, Jick H. Cigarette smoking and the progression of multiple sclerosis. Brain 2005 Mar 9;[Epub ahead of print].
2. National Multiple Sclerosis Society. What is Multiple Sclerosis? Available at: http://www.nationalmssociety.org/What%20is%20MS.asp. Accessed May 6, 2005.
3. Riise T, Nortvedt MW, Ascherio A. Smoking is a risk factor for multiple sclerosis. Neurology 2003 Oct 28;61(8):1122-4.
4. Hernan MA, Olek MJ, Ascherio A. Cigarette smoking and incidence of multiple sclerosis. Am J Epidemiol 2001 Jul 1;154(1):69-74.
John Martin is a long-time health journalist and an editor for Priority Healthcare. His credits include overseeing health news coverage for the website of Fox Television's The Health Network, and articles for the New York Post and other consumer and trade publications.
