Tobacco use
Smoking, including exposure to secondary smoke, is a known risk factor in the development and progression of MS (
Hedström et al., 2013;
Manouchehrinia et al., 2013;
Hernán et al., 2005). People with MS who smoke tend to experience more disease activity, accelerated brain atrophy and increased disability burden, though some negative outcomes may reverse in those who quit (
Rosso et al., 2020;
Rodgers et al., 2021). In addition, smokers may not get the full benefit of MS disease-modifying therapies (
Hedström et al., 2014). Smoking also contributes to co-morbidities and a shortened lifespan in people with MS.
Obesity
Obesity has been identified as a
risk factor for developing MS. There are conflicting data on whether obesity is associated with brain volume loss in people diagnosed with MS (
Mowry et al., 2018,
Galioto et al., 2020). BMI was not associated with processing speed in a large cross-sectional sample (n=8713) (
Galioto, 2020). Additional prospective studies are needed to further clarify the association of obesity with disease progression and clinical outcomes. Due to the established connection between obesity and comorbid conditions, individuals living with MS with an elevated BMI should be encouraged to maintain healthy lifestyle habits.
Comorbidities
Several studies have looked at comorbid health conditions and their potential impact on people with MS. Comorbid health conditions can increase disability (
Zhang et al., 2018, Salter et al., 2020) and potentially shorten the lifespan of someone with MS (
Capkun et al., 2015;
Salter et al., 2016). One clinical trial (n=959) found certain comorbidities (anxiety and hyperlipidemia) were associated with disease activity and a dose-response relationship was observed between the number of comorbidities and relapse risk (
Salter et al., 2020). Vascular, visual, and psychiatric comorbidities in particular increase mortality risk in patients with MS (
Salter, et al., 2016). The incidence rates of diabetes, hypertension and hyperlipidemia are on the rise in the MS population (
Marrie et al., 2016) and have been found to worsen psychiatric comorbidities in MS patients (
Marrie, et al., 2016). The presence of psychiatric comorbidities has been shown to worsen neurologic disability (
McKay et al., 2018) and depression is associated with slower processing speed and worse MRI metrics (
Abbatemarco et al., 2020). Management of comorbid conditions could reduce disability and mortality risk in patient with MS (
Capkun et al., 2015;
Salter et al., 2016).
There is recent evidence of increased risk of some cancers in people with MS compared to the general population (
Grytten et al., 2020,
Marrie et al., 2020) and compared to their siblings without MS (
Grytten et al., 2020); other evidence suggests a decreased risk in the MS population (
Gaindh et al., 2016). Malignancy warnings accompany some
immunomodulating and immunosuppressive therapies, though the connection between these medications and cancer is still unclear (
Magyari et al., 2020). Further study is needed to inform cancer screening recommendations in people with MS.