social determinants of health in multiple sclerosis

Social determinants of health can be classified in several ways but for the purposes of this Review we divide them into two categories: individual factors and structural determinants. Individual factors include characteristics such as gender, race and ethnicity that have an effect on health via an interaction with structural or societal inequalities. Structural determinants are societal infrastructures that influence health; for example, health-care access and social support. Importantly, these two categories are not always clearly divided and bidirectional influences exist between individual factors and structural determinants. For example, a person’s individual circumstances (such as racial background) can influence their place in society and potentially their access to services such as health care. Furthermore, a person’s access to services and infrastructure such as health care or social support can influence how much adverse personal circumstances such as employment status might affect their health.

For the purposes of this Review, we focus on individual-level MS-related outcomes, including clinical (relapses, disability, cognition), radiological (MRI) and patient-reported (quality of life and effect of disease) outcomes. To maintain a clear focus on the person with MS, we do not discuss societal outcomes, such as health economic findings. We review the literature on a range of social determinants of health including gender, race, education, employment, domestic abuse, socioeconomic status, health-care access, food disparities, neighbourhood environment and pollution, social support, and COVID-19 in relation to MS diagnosis, disease progression and disability.

Individual factorsSex, gender and sexuality

MS is more common in women than in men and the sex ratio seems to be widening5. The characteristics of the disease also seem to differ between men and women6; however, a detailed description of these epidemiological observations and their potential biological underpinnings is outside the scope of this Review.

The effect of MS on quality of life seems to vary between men and women. Among people with MS, evidence suggests that women report worse fatigue and anxiety than men, whereas men report greater limitations in walking, dexterity and emotional roles than women7,8. In one study, the relationship between Expanded Disability Status Scale (EDSS) scores and the patient-reported Multiple Sclerosis Quality of Life-54 (MSQOL-54) instrument differed between men and women, suggesting that the relationship between the physical aspects of MS and quality of life is weaker in women than in men8. That societal influences have a role in this gender difference seems highly likely; however, unpicking such relationships is complex and studies have not yet fully addressed this question. It should be noted that the social construct of gender is more complex than a binary biological variable. In the studies described above, researchers focused on cisgender men and women, and a wider scope of study is required to represent all people living with MS.

Sexual and gender minority (SGM) people face unique obstacles in accessing quality health care, which subsequently affects disease-related outcomes9. The effect of intersectionality between chronic neurological disease and sexual and/or gender minoritization has been poorly studied. One relatively small study performed in San Francisco, which examined people who were at risk of sexual and/or gender minoritization, found that the majority of SGM people living with MS reported that their gender identity or sexual orientation did not affect their health care9. Although most of the participants felt comfortable discussing their sexuality or gender identity with their physician, a few reported homophobia or gender discrimination from health-care professionals, limiting their engagement with care and hence their potential access to disease-modifying therapy. Very few participants reported taking part in either SGM or MS support groups9. In a second small study, compared with cisgender participants, transgender participants reported that they were less comfortable discussing sexual health with their doctor, which could affect their quality of life10. From the studies performed to date, there do seem to be differences between gender groups in terms of how MS affects people and how it might influence their interactions with health-care providers. Further work is required to ensure that the effect of gender on MS is better understood, and that services are able to provide equitable and effective care for all people living with MS.

Race and ethnicity

Interest in the relationship between racial and ethnic background and MS outcomes is increasing, particularly in the USA. Several studies have identified worse clinical outcomes in Black, Hispanic and Latinx people with MS than in white people with MS; these observed differences are unlikely to be solely genetic in origin and are far more likely to result from systemic racism across health and other services11. The magnitude of racial and ethnic influences on social determinants of health are likely to differ across countries and regions; these geographic discrepancies must be considered when attempting to draw population-level conclusions12.

Although MS was historically thought to be most common in white people, evidence now indicates that it occurs at higher frequency in minoritized racial or ethnic populations than previously thought13. In the USA, strong correlations exist between race, health-care access and socioeconomic status. Also in the USA, systemic differences in health-care access, socioeconomic inequalities, cognitive biases and racism within health care have been shown to have a role in poorer disease-related outcomes in people from minoritized racial and ethnic groups across multiple diseases14. A multicentre, retrospective study published in 2004, was one of the first to extensively characterize MS in Black Americans15. Compared with white Americans, Black Americans in this study had a slightly older age at onset and a higher prevalence of opticospinal disease, with more rapid disease progression and shorter time to an EDSS score of 6.0. In support of these clinical observations, a longitudinal study in people with MS identified more rapid brain and retinal atrophy in Americans from African ancestral backgrounds than Americans from European ancestral backgrounds16.

A more recent study compared MS mortality rates among five groups that the authors defined by ethnicity and race: non-Hispanic white, non-Hispanic Black, non-Hispanic Asian or Pacific Islander, non-Hispanic American Indian or Alaska Native, and Hispanic17. Among individuals aged under 55 years, non-Hispanic Black Americans had the highest MS mortality rate of all these groups. In another single-centre study, decreased cortical thickness, decreased subcortical volume and decreased cognitive scores were observed in Black Americans with MS compared with white Americans with MS18. Some of these disparities in outcome might be partially explained by disparities in age at disease onset — later disease onset is a known indicator of poor prognosis. Furthermore, compared with white people, Hispanic people were less likely to present with late-onset MS, but more likely to present with motor symptoms at onset, another poor prognostic indicator19. Confounding factors including diagnostic delay, selection bias and other socioeconomic factors, which were not fully addressed in the studies discussed above, are likely to contribute to racial disparities in MS outcome15.

Despite progress in understanding MS in diverse populations, substantial gaps in our knowledge remain. Barriers to filling these gaps include low enrolment of minoritized populations in clinical trials and substantial limitations to many of the current datasets. For example, much of the existing data is retrospective and focuses on measures of physical disability. Research examining other measures such as cognitive dysfunction and brain changes on MRI often have small sample sizes and do not control for socioeconomic status and other social determinants of health, which are inextricably linked to race and might affect outcomes. Furthermore, reference scores and norms used in tests such as detailed cognitive assessments are often based on white control populations. For example, a study examining early cognitive dysfunction in MS used healthy control groups consisting of Black and Hispanic people and found no significant difference in oral Symbol Digit Modalities Test (SDMT) scores between participants with early MS and healthy participants with the same racial background20. Importantly, overall scores were lower in Black and Hispanic people than white people (both healthy controls and participants with MS), possibly a result of the influence of race on other social determinants of health such as educational attainment and socioeconomic status.

In a number of US-based military studies, data on service-connected disability were used to identify people with MS — MS is considered a service-connected disability when it manifests during or within 7 years of military service21. However, receiving a service-connected MS diagnosis is likely to be more difficult for Black people owing to delays caused by racism and inequality within the health-care system. This means that within US military cohorts — often the most complete in terms of data, and used to understand the influence of race22 — biases unrelated to MS could influence findings including those related to MS incidence and prevalence, and age and disability at diagnosis. Existing studies focus on countries without universal health-care systems and with majority white populations. This narrow focus leaves considerable gaps in our knowledge when it comes to non-white-majority countries and those with universal health-care systems, which are still vulnerable to racial biases23.

Education

Evidence suggests that level of education has an influence on clinical outcomes related to MS, but few MS-specific studies have examined the effect of education on patient-reported or health economic outcomes, as discussed in more detail below. Education precedes and influences occupation, income and often wealth; in some studies it is considered a proxy measure of socioeconomic status. Measures of educational level, commonly completion of high school (12 years of schooling in most countries), have been widely used in MS research, and the results of these studies suggest that higher levels of education are protective against disability progression in people with relapsing MS. For example, in a study of 1,372 Belgian people with relapse-onset MS, participants with <12 years of formal education had a higher risk of reaching an EDSS score of 6.0 than participants with >12 years of formal education in a Cox proportional hazards model adjusted for gender, age, age at onset and disease-modifying therapy, although this relationship was not observed in participants with progressive-onset MS24. Similarly, in another study, a lower level of education in Brazilian people with MS was associated with higher EDSS scores, longer disease duration and a higher T2 lesion load25.

However, all of the studies examining links between education and MS outcomes are limited by their design; as with all case–control studies they are subject to ascertainment bias and involve analysis of selected retrospective data. First, reverse causation might explain some of the observed differences, so prospective longitudinal studies are needed to investigate this possibility. Second, low levels of education are associated with exposure to a range of factors that increase the risk of MS and of worse disease outcomes. Such factors include smoking, low levels of health literacy, lack of employment and low socioeconomic status, and the studies performed so far have not been designed in a way that enables researchers to dissect out the contribution of these different relationships. Third, the studies performed to date focused on years of education, whereas quality of education has not been studied in any meaningful way. Last, it is possible that prodromal MS influences educational achievement26 and thus limits access to higher levels of education, which would place people with earlier MS onset at an educational disadvantage.

Employment

Employment is crucially important when considering population health and health inequalities; however, the relationship between employment status and health or chronic disease is complex and bidirectional. Exclusion from the workplace results in material deprivation, and can adversely affect social status and identity27. As we discuss in this section, few studies have examined the effect of unemployment on health outcomes in MS; however, greater disability, as measured by EDSS, has been consistently associated with lower rates of employment28,29. The strength of this relationship varies between and within countries, and more recent data suggest a narrowing in the difference in employment rates between people with and without MS30. Evidence indicates that higher EDSS scores, fatigue31 and cognitive impairment32 are independently associated with a greater likelihood of unemployment in people with MS33, whereas clinical stability is associated with a reduced risk of leaving employment34,35. Progressive MS is associated with a higher risk of leaving employment than relapsing MS29,36,37. Unemployed people with MS seem to have a higher number of physical comorbidities than employed people with MS38; however, the results of one study suggest that this difference is substantially reduced after adjustment for MS symptom severity, suggesting that the comorbidities and MS symptoms do not act independently37. Furthermore, most studies performed to date compared sociodemographic, clinical and psychosocial variables between employed and unemployed people with MS, using employment status as the outcome variable, which means they did not examine the true complexity of any relationship.

In one study, people with MS who were not working at 10 years after diagnosis had a significant reduction in functioning (in terms of bodily function, as well as activities and participation in activities of daily life), an increased self-reported effect of MS and decreased fine hand function compared with people with MS who were working at this time point39. Another cross-sectional study identified increased perceived stress, reduced self-reported physical and mental health related quality of life, and decreased life satisfaction in unemployed people with MS compared with employed people with MS40. The results of another study indicate that employment status is the most important variable for predicting mental health status in people with MS under 45 years of age41. Similar to education, we note that employment status is associated with a number of risk factors for MS development and subsequent disability such as smoking and low health-care literacy; however, the studies performed to date have not addressed this relationship.

Evidence indicates that other social determinants of health interact with the relationship between employment and MS. For example, younger age and higher education level are consistently associated with a higher employment rate in people living with MS29,36, and in one study a high frequency of social or lifestyle activities at baseline was associated with a greater likelihood of being employed 10 years later31. Studies that investigated sex differences in the likelihood of leaving employment as a result of MS reported a range of results, including no difference, greater likelihood in men and greater likelihood in women29,34,42. In a study of people with MS in the USA, non-Hispanic white people had higher employment rates (48%) than Hispanic people (45%) and non-Hispanic Black people (36%)43, highlighting the potential role of other sociodemographic factors in determining employment status.

Socioeconomic status

Socioeconomic status refers to relative position within the social hierarchy and is measured by indicators such as income, occupation and place of residence. Therefore, socioeconomic status draws on multiple social determinants of health, but it also exerts an independent effect. Evidence has shown that socioeconomic status has an effect on health across a wide range of indicators, settings and populations44. Although reducing socioeconomic inequalities in health is an international policy priority, large disparities persist in both countries with and countries without universal health-care systems45.

To date, studies investigating the relationship between socioeconomic status and MS have mainly focused on the risk of developing MS. Overall, findings are conflicting, with some studies finding an association between high socioeconomic status and risk of MS, some finding an association between low socioeconomic status and risk of MS, and others finding no association46,47. In a meta-analysis published in 2015, all the studies that identified a link between high socioeconomic status and MS risk were from countries that were considered to have more inequality; a potential explanation for this relationship could be differences in the skills that are required to navigate complex health-care systems or differences in insurance status in payer-based systems.

Available data regarding the effect of socioeconomic status on MS disability outcomes indicate a relationship between greater deprivation at disease onset and greater disability even in countries with a universal health-care system, including a higher risk of reaching EDSS scores of 4.0 and 6.0 in Cox proportional hazards models46,48, faster retinal neurodegeneration49 and onset of secondary progression46. Evidence also indicates that higher socioeconomic status in people with MS is associated with a lower burden of psychiatric symptoms and a higher likelihood of symptom recovery following mental health treatment50,51.

In regions without universal health care, lower socioeconomic status is associated with reduced access to highly effective disease-modifying therapy for MS52. People living in poverty are less likely than other people to be able to access insurance systems that cover comprehensive disease-modifying therapy, and large studies have shown a direct effect of this disparity on cancer outcomes53. Therefore, the relationship between socioeconomic status and disability in MS could be mediated by access to disease-modifying therapy. However, this hypothesis is still a matter of debate and the mechanisms underlying the relationship are likely to vary substantially within and between geographical regions. The results of some studies indicate that, in countries with a universal health-care system, people with MS with higher socioeconomic status are more likely to be prescribed disease-modifying therapy and less likely to experience delays in disease-modifying therapy escalation than people with lower socioeconomic status54,55,56; however, other studies have found no evidence to support this conclusion57,58. These contrasting results are likely to be related to the specific scope and limitations of individual studies, along with differences in local prescribing ‘cultures’. Evidence also suggests that socioeconomic status-related disparities in disease severity, health-care access and literacy can affect prescribing decisions in MS54,57,58; however, research into ways to overcome barriers and/or enact local change is lacking.

Substantial associations exist between socioeconomic status and MS disability risk factors, such as smoking, obesity and comorbid disease, which might influence any observed relationship between socioeconomic status and disability outcomes. Most studies that examine the relationship between socioeconomic status and MS diagnosis or disability outcomes do not control for these risk factors59. As mentioned above, comorbidities have been associated with poorer long term outcomes in MS60; actively addressing these, especially in more deprived populations, is a potential means through which MS outcomes could be improved. The relationship between socioeconomic status and MS diagnosis and disability is not unidirectional; evidence from the UK MS Register indicates that MS restricts social and economic opportunities, even several years before diagnosis61 (Fig. 2). Critical study of the timing and mechanism(s) through which socioeconomic factors might exert their influence on MS outcomes, along with means by which neurology teams can intervene to ameliorate these, thus has the potential to markedly change outcomes for many people living with MS.

Fig. 2: Potential interactions between selected social determinants of health and multiple sclerosis outcomes.figure 2

Many social determinants of health interact and intersect with each other, leading to poorer outcomes, in either an additive or even a multiplicative manner. There are potential further interactions between living with chronic multiple sclerosis symptoms such as cognitive impairment and bladder or bowel impairment, and social determinants of health. Multiple sclerosis and its symptoms might reduce an individual’s social determinants of health, particularly those related to employment and social isolation, which might then amplify the effect of multiple sclerosis. Studying this vicious cycle is complex owing to the multiple and varying influences that exist at both the individual and group level.

Domestic abuse

Domestic abuse is defined as “a pattern of behaviour in any relationship that is used to gain or maintain power and control over an intimate partner”, which can be “physical, sexual, emotional, economic or psychological actions or threats of actions that influence another person”62. This abuse has a serious effect on the individual, the family and the health-care system; however, no data on domestic abuse and disease-related outcomes in MS have been published to date.

According to data from Public Health England, people with disabilities experience disproportionately higher rates of domestic abuse over a longer period of time, with greater severity and frequency, than non-disabled people63. In addition to practices such as gaslighting and physical abuse, less widely recognized forms of abuse, such as ridiculing or physical neglect, have been reported64. Domestic abuse can involve a range of people including intimate partners, family members and carers, and disabled women are much more likely to experience abuse than disabled men63. In a survey of US adults with advanced MS, more than half of the respondents reported abuse from their caregivers65, and the WHO has identified substantial barriers to disabled people seeking support after abuse66. Further research is needed to understand the best and most sensitive means of applying this knowledge across clinical practice in MS; although this is a challenging area, given the potential risk that people living with MS are at, it is clearly important.

Intermediate determinantsHealth-care access

Health care for people living with MS includes not only care associated with MS management, but also care of any comorbidities, health screening and preventive care, and access to services for transient acute health issues. Studies of health-care access that consider the progression of MS as an outcome of interest have investigated access and the use of neurologists67, investigation and treatment of MS-related bladder symptoms68, and the use of disease-modifying therapy58,69. Other studies have investigated access to cancer screening, management of hypertension and osteoporosis in women with severe MS70, general health needs71 and social support72; studies addressing health care are discussed in more detail below.

In a US-based study, participants with lower levels of MS-related disability were more likely to receive their usual care directly from a neurologist, and those with higher disability were less likely to receive medical care

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