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How Smoking Makes Multiple Sclerosis Worse

Some Proposed “Mechanisms of Action”

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Updated February 23, 2009

I’ll start by saying that smoking does not cause multiple sclerosis (MS) -- at least not by itself. If you could get MS just from smoking, it is pretty likely many more people who smoke would have it, and many fewer people who never smoked would not have it.

However, there is very convincing evidence that smoking contributes to the development of MS and the progression of MS, especially when people start smoking very young. Cigarette smoking causes some symptoms of MS, such as respiratory problems and erectile dysfunction, to be worse. It increases the already-elevated risk of a person with MS to develop osteoporosis. Smokers who have MS are also shown to have greater disability, as measured by the Expanded Disability Status Scale (EDSS), and have a lower brain volume than non-smokers. Smoking is associated with higher risk of autoimmune disease, not only MS, but some forms of rheumatoid arthritis, lupus and autoimmune thyroid disease (Grave’s disease) and Crohn’s disease).

Since the exact causes and disease mechanisms of MS are not known, it is impossible to state what it is that smoking does that increases the risk or severity of the disease. It could be that it stimulates or suppresses the immune system of people who are already genetically susceptible. It could be that it makes people more vulnerable to certain infections that send the immune system off in the wrong way, maybe Epstein-Barr virus or some sort of respiratory infection. It could be (and this is my least favorite theory, and one that I find pretty annoying) that smoking is simply correlated with a whole bunch of other habits and characteristics that are the true “causes” of MS.

Some Theories About How Smoking Causes MS-Specific Damage

Nitric Oxide: One theory is that smoking may worsen MS by increasing nitric oxide (NO) in the body. Smoking cigarettes increases levels of NO in the plasma. While NO is an important and essential chemical in our bodies, helping to signal blood vessels to dilate, delivering oxygen to tissues, and transmitting nerve impulses, it is also a free radical. High levels of NO are neurotoxic and have been associated with damage of axons in people with MS. It is also a cerebrospinal fluid marker for MS progression, meaning that levels are higher in people with more progressed disease. Axons that are demyelinated or inflamed are particularly vulnerable to damage or destruction from NO.

Acrolein: A nasty chemical in cigarette smoke is acrolein, which is proposed to directly lead to neurodegeneration. It causes lung irritation and tearing of the eyes to the extent that it was used as a chemical weapon during World War I. It has also been linked to immunosuppression, which can alter the functioning of the entire immune system.

Leaky Blood-Brain Barrier: It has also been thought that nicotine in cigarette smoke might increase the permeability of the blood-brain barrier to the point that abnormal T cells could cross it.

Greater Vulnerability to Infection: Smoking makes people more vulnerable to respiratory infections from viruses and bacteria, both by damaging the protective mucous membranes and through general immunosuppression. Although we don’t know exactly which germ is directly involved with causing MS, many experts think that a viral infection could be a big part of what starts MS rolling in many people by stimulating the immune system in the wrong way.

Smokers Have “More Fun”: One theory goes that people who smoke also engage in all sorts of other behaviors that could contribute to developing or exacerbating MS, such as drinking more alcohol; eating more poorly; getting less exercise; having a lifestyle that minimizes vitamin D exposure and exposes them to certain viruses, etc. This has all been lumped into what has been referred to as “impulsive seeking traits” or “risk-associated behavior.” This is the theory I am the most skeptical about, really.

Bottom Line

I suppose I don't really have to list all of the reasons that smoking is simply a bad idea, especially for those of us who already have a chronic illness. Most of you who smoke are probably quite aware that smoking is causing damage to your health, not only in terms of your MS. There are different approaches to quitting and a variety of resources to help you stop smoking. With that, I'll hand you over to my colleague at About.com's smoking cessation site, quitsmoking.about.com. I'm sure you'll be in good hands.

Sources:

Sundström P, Nyström L. Smoking worsens the prognosis in multiple sclerosis. Mult Scler. 2008 Sep;14(8):1031-5.

Koch M, van Harten A, Uyttenboogaart M, De Keyser J. Cigarette smoking and progression in multiple sclerosis. Neurology. 2007 Oct 9;69(15):1515-20.

University at Buffalo (2007, October 14). Cigarette Smoking May Accelerate Disability In Those With MS. ScienceDaily. Retrieved February 16, 2009, from http://www.sciencedaily.com¬ /releases/2007/10/071013083426.htm.

Hawkes CH. Smoking is a risk factor for multiple sclerosis: a metanalysis. Mult Scler. 2007 Jun;13(5):610-5.

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