It is universally acknowledged that smoking is bad for your health. It is a known cause of serious illness and premature death, both of which could be preventable in its absence.
The latest figures show that in England alone, 15 per cent of all deaths in people aged 35 and over per annum were attributable to smoking (1). In Scotland, this figure was slightly higher at 21 per cent (2).
The list of diseases caused or made worse by smoking is vast. Many of them are fatal or at the very least cause permanent long-term health damage. Smokers are at an increased risk of contracting coronary heart disease, strokes and a variety of cancers. They are also at an increased risk of being affected by circulatory diseases and those which affect the digestive system (1).
For people with multiple sclerosis (MS) there are even more compelling reasons to quit, given the evidence that demonstrates smoking is an environmental risk factor which contributes to MS onset and disability progression (3). Indeed, a recent study concluded that just over 10 per cent of MS diagnoses could be prevented through the avoidance of smoking (4).
Smoking is also associated with a reduction in brain volume, can lead to a higher relapse rate and more cognitive problems (5).
More information Our Cognition Choices booklet provides a focus on how MS impacts cognitive processes, which includes evidenced-based information on the part that smoking plays in this.
There is a compelling body of evidence which has shown the link between the development of MS and smoking.
In 2003 a study was published which looked at the increased risk of developing MS in people who smoked within the general population. This study followed over 22,000 people in Norway, all of whom completed a detailed questionnaire about past and current smoking habits and were given a physical examination.
The study found that of the 87 people who developed MS, only two had not smoked at some point during their pre-diagnosis lives.
The authors concluded that there was an increased risk of developing MS associated with smoking. For men the risk was three times greater than for a male non-smoker, and for women, the risk was one and a half times greater. The theory behind these results was that smoking may damage the cells which line blood vessels and these damaged cells cause the vessels to leak, allowing the toxins found in cigarette smoke to damage the brain (6).
Two more recent studies provide further evidence of the link between smoking and MS onset.
In 2016 a meta-analysis of previous studies was published. It incorporated over 20,000 cases and concluded that exposure to tobacco smoke is an important risk factor in MS development (7).
Earlier we briefly referred to a study which concluded that some people could avoid developing MS if they did not smoke (4). The study involved a population of just under 20,000 individuals based in Sweden, evenly split between those who had received an MS diagnosis and those who had not. The authors looked at information provided by the participants which reflected their current and previous smoking habits, and where possible, considering their MS genetic risk scores.
Given the study’s findings, it was calculated that if they were replicated on a worldwide scale, approximately 364,000 of the 2.8 million people with MS could have potentially prevented themselves from developing the condition had they avoided smoking tobacco. While these figures are projected, they do reflect the significant role that smoking can play in the development of MS.
The connection between smoking and disability progression for people affected by MS has been known for a while. In 2005 the results of a control study were published, suggesting that smoking contributes to the progression of MS (8). The researchers examined the medical records of almost 2,000 people in the UK, including 179 people with relapsing remitting MS (RRMS).
Researchers found current or former smokers with RRMS were over three times more likely to develop secondary progressive MS (SPMS), another phase of MS marked by a steady increase in MS symptoms and disability, compared to those who had never smoked (8).
One of the central theories behind these results, supported by previous studies at the time, was that nitric oxide (NO), a chemical found in cigarette smoke, may be responsible for damage to the cells that create myelin, the protective coating around a nerve cell. The study concluded that their findings warranted further investigation into the connection between smoking and MS progression.
Fast forward to 2015 when the results of a cross-sectional study were published. The study was conducted between 2008 and 2011 and involved 728 RRMS patients based in Sweden, all of whom were active smokers at the time of diagnosis. After their MS diagnosis 332 of the 728 people in focus continued to smoke. The evidence found was compelling, in that for each year a person smoked after their MS diagnosis, the time it took for their condition to progress to SPMS accelerated by almost five per cent, in comparison to those who had chosen to quit the habit (9).
The findings of these previous studies were underpinned by one that took place in the UK which was published in 2021. This study took data from the United Kingdom Multiple Sclerosis Register (UKMSR) and analysed information provided by almost 8,000 people with MS. The headline finding from this study was that smoking does indeed contribute to accelerated deterioration in MS related conditions, including motor disability. However, when a person quits the habit there was strong evidence which showed their rate of decline decreases and eventually matches that attributed to non-smokers (10).
In 2007, research from France linked children’s exposure to passive smoking and an increase in their chances of developing MS in later life (11). It found that 62 per cent of the study population who were diagnosed with MS had been exposed to parental smoking as children. For those who had not been exposed to parental smoking in childhood that figure fell to 45 per cent.
The research also pointed to a time-related correlation between the increase in the risk of developing MS as an adult and the length of time a child had been exposed to passive smoking.
More recently research conducted in Denmark underpinned the link between the intake of second-hand smoke in childhood with the development of MS in adulthood. Interestingly this research found that this risk of developing MS was higher in females who were exposed regularly to passive smoking compared to males (12).
There is a growing body of evidence which shows that smoking can impact the efficacy of DMTs.
For people taking the disease-modifying drug natalizumab (Tysabri), there is evidence that smoking increases the risk of the body developing neutralising antibodies to the therapy, causing the drug to have little or no therapeutic effect. A Swedish study published in 2014 looked at just over 1,000 people with MS who were on a natalizumab treatment programme (13). It found that the risk for developing these neutralising antibodies was over twice as high in smokers, compared to non-smokers.
Advice given at the 2014 joint ACTRIMS/ECTRIMS conference, following the results of this study, was that a person should not be prevented from starting natalizumab treatment if they smoked. However, it was noted that if the treatment proved ineffective due to the presence of antibodies, other therapies should then be considered (14).
A more recent study undertaken in Denmark, published in 2018, also examined the link between smoking and the onset of relapses for natalizumab-treated RRMS patients. Over a two-year period they studied the relapse activity of 355 participants, comprising smokers and non-smokers, all of whom were receiving natalizumab treatment. This study found that relapses were much more common in the participants that smoked as opposed to the non smokers, with a relapse rate increase of 38 per cent in those that smoked 20 cigarettes per day (15).
There is a similar story regarding other DMTs. Again in 2018 another Danish study focused on over 800 people with RRMS who were undergoing beta interferon treatment. The authors found that those who were active smokers experienced a 20 per cent increase in relapses in comparison to non-smokers (16).
In 2023, the results of an observational study based in Japan, undertaken between January 2012 and December 2019, were published (17). The study was concerned with looking at how smoking may impact on the efficacy of the DMTs fingolimod (Gilenya) and dimethyl fumarate (Tecfidera). Over 100 people with RRMS took part in the study with their clinical data and smoking status observed throughout the study period. It was found that once DMT treatment had started, those who continued to smoke experienced their first relapse and disease activity much sooner than those who did not smoke.
Significantly, the study’s authors concluded that even if a person was an active smoker at the time they started taking their course of DMT, the sooner they quit smoking the more they will benefit from the treatment.
More information Our Disease modifying therapies Choices booklet provides further reading about the different DMT’s that are used to treat MS
In recent times there has been growing evidence of the role that gut health plays in keeping our bodies healthy, but even more importantly, its importance in managing the impact of conditions such as MS. We explain much more about this relationship in our Choices booklet ‘Diet and supplements’
To date, scientific research has found that the toxins contained in cigarette smoke unsettle the gut microbiota balance, helping to induce dysbiosis (18). This can lead to bacteria escaping from the gastrointestinal (GI) tract via the intestinal barrier and leaking into the bloodstream, with the effect being an increase in inflammatory influences on the central nervous system.
More information Our Diet and supplements Choices booklet provides more information about the link between gut health and MS, plus details of how you can bolster your gut composition.
Although it may be difficult to stop smoking, as we have identified in this booklet, this lifestyle change can lessen your risk of developing MS. If already diagnosed, stopping smoking could help to decrease your risk of disability progression.
Researchers at University College London published a report in 2017 which states that success rates for giving up smoking were at their highest for over a decade. In the first half of 2017, nearly one in five attempts at quitting smoking were successful (19).
It is suggested that some of this success has come from the use of e-cigarettes. In 2019 the Office for National Statistics reported that around 3 million people in the UK regularly used e cigarettes, with approximately half using them as a smoking cessation aid (20).
Whilst e-cigarettes are a relatively safe alternative to smoking tobacco and are highly regulated within the UK to ensure their quality and safety, there are still risks associated with their use. The liquid and vapour that they produce can contain chemicals that are potentially harmful, but on a lower level when compared to levels found within the smoke produced by conventional cigarettes (21).
There are a range of smoking cessation support services based around the UK. These offer access to professionals who are trained in supporting people to quit. Your GP, hospital and local pharmacy will also be happy to advise you on what may be the best course of action to help you stop smoking.
More information If you smoke and want to quit, the NHS Better Health website provides a range of information and advice to help you stop. This includes details about the different methods you can use to quit smoking, where to find localised support and links to their very handy NHS Quit Smoking app.
Quit Your Way Scotland is an advice and support service to help people in Scotland to stop smoking.
Help Me Quit Wales is a multi-lingual smoking cessation service run by Public Health Wales.
Stop Smoking NI was developed by the Public Health Agency to provide smoking cessation support for people based in Northern Ireland.
