Most of the evidence points to smoking as a contributing factor for developing multiple sclerosis. However, once it is a done deal and you have been diagnosed with MS, does smoking still matter?
Yup, looks like it does.
Smoking Makes MS WorseA 2009 study conducted by the Partners Multiple Sclerosis Center of Harvard and Brigham and Women's Hospital is the largest research effort looking at the effect of smoking on people with multiple sclerosis. The study included 1,465 participants with MS, who had been diagnosed with MS for an average of 9.4 years. There were 257 current smokers, 428 past smokers and 780 participants who had never smoked.
Progressive Disease: The Partners MS study showed that current smokers were 2.41 times more likely to have primary progressive MS than people who had never smoked. In another study where 122 people with MS were followed for 6 years, people who ever smoked were twice as likely to have progressive MS than people who never smoked. This was supported by a study that showed that people who started smoking early in life (when they were 15 years old or younger) were significantly more likely to be diagnosed with progressive disease and be diagnosed earlier than people who started smoking later in life. They also were more likely to be diagnosed with primary progressive disease from the outset, rather than with relapsing-remitting MS. Interestingly, the ratio of men to women with PPMS is 1:1 (compared to 1:2 for RRMS) - some researchers theorize that this is because there are more male smokers and smoke contributes so much to the risk of PPMS.
Progression to SPMS: The Partners MS study also found that current smokers with RRMS (relapsing-remitting MS) progressed to SPMS (secondary-progressive MS) 2.5 times faster than people who had never smoked. More specifically, a subgroup of 891 study participants with RRMS were followed for an average of three years to identify how many progressed to SPMS. During the follow-up period, SPMS was diagnosed in 20 of 154 smokers (12%), 20 of 237 ex-smokers (14%) and 32 of 500 never-smokers (6%).
Another study followed 179 people with RRMS for about 5 years, finding that people who ever smoked were 3.6 times as likely to develop secondary-progressive MS than those that had never smoked.
Brain Volume: A study from University at Buffalo compared MRIs of people who had never smoked (240) to people who had formerly smoked (32) and those who were active smokers (96). They found that people who had ever smoked had lower brain volumes than people who had never smoked, with no differences in any of the clinical findings between active smokers and former smokers. These findings were supported by the Partners MS study.
Increased Disability: The Partners MS study found that current smokers had significantly worse disability at enrollment, and that they accumulated disability faster than non-smokers, (as measured by the Expanded Disability Status Scale – EDSS and Multiple Sclerosis Severity Score - MSSS) at baseline, two and five years. The Buffalo study also found that people who ever smoked had significantly more disability (higher EDSS scores).
Interestingly, another retrospective study with 364 participants looked at the correlation between smoking and MS progression/disability and concluded that cigarette smoking did not influence disease progression or accumulation of disability.
The Bottom Line
In an ideal world, if you quit smoking, damage can be reversed and risks for certain things can be lowered, which is sometimes the case in cardiovascular disease and cancer risks. The case in MS seems a little “muddy” around the amount of "damage control" smokers can do by quitting, in that some measures of disability were no different in people who smoked and people who had quit, with both groups having more disability than people who had never smoked.
However, in the Partners MS study, the rate of progression from RRMS to SPMS was similar in ex-smokers and people who had never smoked, indicating that quitting may slow down this process.
There also seems to be a “dose-response,” meaning that the amount that someone smokes is also a factor. For instance, the Buffalo study showed that the more packs per day that someone smoked, the more atrophy there was of the neocortex (the part of the cerebral cortex that controls executive functioning), meaning that smoking seems to accelerate brain atrophy. This implies that if a smoker quits or cuts back, they can at least preserve some of this cognitive functioning. An Australian study among 203 people with MS had similar findings – people who smoked the equivalent of two packs per day accumulated three times as much disability as people who smoked less than one pack per day, as measured by the MSSS.
In addition, smoking can make many MS symptoms worse, such as: respiratory dysfunction, loss of smell and erectile dysfunction. Not preaching, of course – just saying. If you do decide that you’d like to try to quit, I’ll recommend About.com’s smoking cessation site, quitsmoking.about.com.