Work as a social determinant of health on cardiovascular and musculoskeletal diseases: A literature review

The health effects of unemployment and job insecurity

A bad or negative work environment can contribute to the risk of CVD including stroke, which is associated with an increased prevalence (OR = 1.29, p < 0.01). ²¹ Although somewhat sparse, the majority of research studies on job insecurity and unemployment has been restricted to industrialized societies, like the U.S.^22,23 Additionally, the specifications on the frequency and length of job insecurity and unemployment are lacking, which make it challenging to fully understand the impact on health. ²² While poor health in and of itself can be a cause of unemployment, studies also show that unemployment appears to be an independent factor of preexisting health effects. ²⁴ Unemployment brings lower income and living standards, which consequently can cause deteriorating physical health because of changes in the ability to afford nutritious food, healthy housing, and/or sufficient medical care. This was particularly evident during the COVID-19 pandemic, when in October 2021, nearly 20 million adults lived in households that did not get enough to eat, 12 million adult renters were behind on rent, expired unemployment benefits, and supply chain problems that contributed to rising prices on common goods. ²⁵

What we do know is that unemployed individuals have a higher prevalence of poor health and excess mortality than their employed counterparts.^22,23,26 Unemployment is associated with health issues such as cardiovascular risk factors, being overweight, and having diabetes ²⁷ and it can limit access to health-promoting aspects of work. In addition, those who are already at greater disadvantage with respect to social factors like educational attainment and racial or ethnic group are at greater risk of being unemployed. ²⁴

For those who are employed, job insecurity or even the threat of job loss can contribute to poorer health. ²⁴ Job insecurity has been shown to be associated with elevated risks of hypertension and cardiovascular disease”.^28,29 Specifically, job insecurity is significantly associated with elevated hypertension among those employed in healthcare support occupations ³⁰ and public administration industries. ³¹ The stress associated with the prospect of losing one's job can also lead to risky coping behaviors such as smoking, lack of exercise and forgoing sick or vacation leave, and may place workers at increased risk of work-related injury and illness. ³² In a study of hotel housekeepers, agency-hired workers typically received no benefits, are paid less, and experienced job insecurity, thus having more difficulties in maintaining routine medical visits and purchasing prescription medications. ³³ In situations of economic and sociopolitical instability, single women are the most vulnerable, often having little to fall back on in the face of illness, job loss, and increased family care and domestic burdens. ³⁴

The impact of shift work schedules on health

Shift work is typically characterized by employes working outside standard (9:00am to 5:00pm) hours. Because shift work includes night work, the normal sleep—wake cycle circadian rhythm is disrupted, with potential consequences for shift workers’ physical health. ²⁹ Evening and overnight shifts, holding multiple jobs, long work hours and excessive overtime work can be detrimental to health by causing increased fatigue, sleep loss or lower sleep quality, decreased work performance, occupational stress, and disturbances in circadian rhythms.^24,35–39 Workers with physically-demanding jobs—including long hours, strenuous occupational physical activity, and irregular working hours—are more likely to experience a stroke, hypertension, or other cardiovascular diseases compared to other workers.^29,35–41

The research on working hours and health appears to be evident. Specifically, there is a significant association between stroke and exposure to long working hours for 10 years or more, ⁴¹ and regular (non-shift) employment before stroke onset appears to have a positive impact on outcome. ⁴² It has been shown that longer working hours and an extended duration of strenuous activity during work is associated with increased rates of hemorrhagic stroke.^32,41 This issue becomes even more urgent during and after the COVID-19 pandemic, as individuals are working more from home, with the risk of working longer hours and becoming physically inactive. ⁴² Health promotions advocate for consistent physical activities, breaking up sedentary time and maintaining social relationships, beneficial to public mental health. ⁴²

We also see gender and other demographic differences in health, as it relates to shiftwork. In men, systolic blood pressure was higher in shift workers compared to daytime workers; and in women, weight, body mass index, and the prevalence rate of hypertension in the past medical history were higher in shift workers compared to daytime workers. ³⁶ And for both men and women, rotating shift workers spent less time sleeping both on working days and on non-working days, spent less time with sport activity, drank more coffee and they spent less time working per day, especially in light physical work, compared to daytime workers. ³⁶ In addition, low and middle educational levels were most frequently found among rotating shift workers as opposed to daytime workers where high educational level was more common. ³⁶

The balance between work effort and reward

Perceived balance between a worker's efforts and rewards (in terms of earnings, benefits, esteem, job security and career opportunities) has been shown to influence health outcomes. ²⁴ Effort reward imbalance exposure and high efforts at work has been associated with heart disease ³⁷ and masked hypertension, ⁴³ and for women, effort reward imbalance was associated with higher increases in systolic ABP. ⁴⁴ Interestingly, all three measures of effort and reward imbalance, job strain, and conflict at work, were more frequently reported among stroke cases. ⁴⁵ However, the mechanisms by which this imbalance differs, might be due to gender or other demographic factors (i.e., socioeconomic, racial/ethnic factors, etc.) which should be further examined.

The psychosocial work environment

Evidence shows associations between work environment, physical indicators and mental health outcomes. ⁴⁶ Despite the influence of the work environment, there are still limited studies exploring the work environment comprehensively. Research shows that the work environment can be a risk factor for the development of moderate to severe clinical conditions, predicting absenteeism or intention of leaving the job. ⁴⁷ Specifically it has been shown that a poor work environment and cardiovascular disease risk factors (obesity or sleep complaints) occur not only when workers are exposed to poor working conditions, but also after retirement. ⁴⁶

Literature on the psychosocial work environment is still a matter of debate. In particular, the involvement of the main behavioral and clinical risk factors and their relationships with working conditions are not always clear, despite an abundant body of literature. ⁴⁶ Most studies have investigated the impact of a limited number of characteristics of the work environment on the occurrence of one or a few risk factors, dismissing potential mediating factors. ⁴⁶ Some of these psychosocial work environment investigations have targeted specific populations, such as nurses, ⁴⁸ and home care workers, ⁴⁹ but studies with more robust designs are needed. ⁴⁷ Nevertheless, more research into the psychosocial work environment is needed to improve the health of working populations. ⁵⁰

The influence of control at work, demands, and decision latitude on worker's health

Job control, the combination of skill discretion and decision authority, is considered a central component of the psychosocial working environment. ⁵¹ Differences in the degree of control that workers feel they have over their working conditions are thought to be a major factor accounting for steep social gradients in health. ²⁴ Jobs characterized by both high psychological demands and high levels of decision-making authority and skill utilization (“decision latitude”) can promote self-esteem and self-efficacy; yet workers whose jobs have high demands offer little decision latitude (what has been called “job strain”), are at higher risk of chronic physical and mental illnesses (such as cardiovascular disease, stroke, hypertension and musculoskeletal pain).^24,52

Employes who feel their job gives them little job control yet have high demands have been found to have increased risks and worsened outcomes relating to cardiovascular disease, hypertension, and cerebrovascular disease.^28,37,45,53 The same is true of workers who feel that the benefits of their work do not align with their efforts.^{25,26,34,54,55} Men appear to be more impacted by these psychosocial exposures than women, ⁵³ though women represent an understudied population. ⁵⁶ Research is needed to determine the impact of the timeframe of these exposures on cardiovascular and cerebrovascular events.

Literature provides evidence of gender and/or age differences in such outcomes. For example, low job control was associated with an increased risk of hypertension among men, but not among women. ⁵³ But low job control was associated with upper-limb pain among women, while high psychological demand was associated with upper-limb pain only among men. ⁵⁷ The prevalence of upper-limb pain was higher among those women who performed passive work (low demand, low control), active work (high demand, high control), and tasks under high strain (high demand, low control). ⁵⁷ For women, there appeared to be a relationship between both lower back pain and neck-shoulder pain with job control, revealing that higher levels of job control were related to lower levels of both low back pain and neck-shoulder pain.^11,52 Research also found that high emotional demand led to excess risk of workplace injuries, with this risk highest for workers under the age of 30, for males declaring a fear for their own safety or for the safety of colleagues and females who work in an atmosphere of tension with the public, or who have to hide or fake emotions. ¹²

The link between health and the physical risks and hazards of work

There is widespread awareness that both physical tasks involved in a job and the physical work environment can have important health effects, which has been the traditional focus of occupational health and safety research. Physical factors are social determinants of workplace injury, with the higher the reported exposure to physical risk factors, the higher the risk of workplace injury. ¹² There are also other hazardous exposures in the workplace: inadequate ventilation or temperature control which exacerbate allergies or asthma, lead, pesticides, aerosols, ammonia, asbestos, and other cleaning products and workplace-related chemicals which can create long-term exposure can poison and cause serious illness. ⁵⁸ Park et al. (2019) reported more exposure to physical/chemical and ergonomic hazards and musculoskeletal pain for those in nonstandard employment. ⁵⁹ Workers with physically-demanding jobs—including long hours, strenuous occupational physical activity, and irregular working hours—are more likely to experience a stroke, hypertension, or other cardiovascular diseases compared to other workers.^28,35–40 Individual demographic and work characteristics (i.e., age, gender, type of work, skill level, exposures at work) are important factors related to health outcomes. For example, a higher level of physical exertion is a risk factor among older female eldercare workers, but a moderate level of emotional demands is associated with lower risk among younger workers. ⁶⁰ Work that is physically demanding and poor workplace conditions are associated with a higher prevalence of pain among both women and men. ⁵⁷ Additionally, employes with musculoskeletal pain had 4 times higher risk of disability pension compared to those without musculoskeletal pain. ⁶¹ However, limited longitudinal studies have identified relevant hazard and risk factors for musculoskeletal pain. ⁶² To ensure the development of a more nuanced approach to hazard reduction and improved sustainable employment for workers requires a greater understanding of the relationship between work characteristics and musculoskeletal pain. ⁶²

Workers in particular areas of the workforce are at increased risk of work-related injuries and illness: air transportation, nursing, ⁶³ work with motorized vehicles and equipment, trucking services, hospitals, grocery and department stores, and food services account for nearly 30 percent of nonfatal occupational injuries. ⁶⁴ Physically demanding daily tasks and uncomfortable working positions can lead to physical strain and injury, increasing the risk of long-term absence, mostly due to musculoskeletal pain; and sedentary jobs allow little opportunity for movement and contribute to risk of obesity and chronic diseases like diabetes and heart disease. ⁶⁴ For example, among standard and nonstandard workers overall, unskilled manual workers were more likely to be elderly, less educated, have a low income, work fewer weekly hours, and have a shorter work duration, service. ⁶⁵ Sales workers were more likely to be younger, have a shorter work duration, and work in smaller workplaces; and clerks were more likely to be younger and more educated; and managers and professionals were more likely to be more educated. Manual workers were more likely to report exposures to all physical/chemical and ergonomic hazards, and musculoskeletal pain than non-manual workers and have a higher income. ⁶⁶ Blue-collar workers are more at risk (than white-collar workers), with a significantly higher prevalence of musculoskeletal symptoms ⁶⁷ and an increased risk of hemorrhagic stroke. ³⁵

Need for future studies

Our analyses reveal the need for prospective/longitudinal design and modeling for predicting workplace injuries so that preventative measures can be preemptively applied to minimize combinations of psychosocial and physical risk factors. For example, objectively quantifying the early signs of pain can have a major impact on functional abilities. Having tools for early detection of musculoskeletal disease pain and functional impairment will allow delivery of preventative approaches at a pre-clinical stage. Wearable sensor technology coupled with custom software and biomarkers of ageing can objectively quantify early signs of pain associated with detrimental impact of functional abilities. Having such tools of early detection of musculoskeletal disease pain and functional impairment will allow delivery of preventative approaches at pre-clinical stage.

The physical health and mental health implications of balancing work and family responsibilities

Given the persistent gender imbalance in family care responsibilities among women, ⁶⁸ and that women are more adversely affected by rheumatic and musculoskeletal diseases compared to men,^57,68,69 makes gender in musculoskeletal health a priority area of future research. Within a study group of women, there was a higher prevalence of pain among those exposed to a high domestic workload. ⁵⁷ For women, supervisor support is protective against lower back pain, but only when work-family conflict is low; whereas for men, experiencing moderately high levels of work-family conflict amplified the negative effects of physically demanding work on lower back pain. ⁵²

The impact of the pandemic continues to affect many workers, with greater concern for safety at work around the COVID-19 infection and related organizational changes affecting their jobs. ⁷⁰ The literature highlights the nexus of health and gender inequalities associated with the COVID-19 pandemic and the adverse impact on women's health in balancing work and family responsibilities. Women performing work from home and family responsibilities during the lock down seemed to be going through increased physical and mental load. ⁶⁸ However, social support at work has protective effects on health and has been linked to reduced risk of illness-related absence.^71,72 Work environments that facilitate mutual support between coworkers can reduce job stress and provide a buffer against physical stressors related to work. ²⁴ Support from supervisors has additionally been shown to help workers manage their hypertension. ³³ Having a good physical work environment and good relationships with management were associated with self-reported musculoskeletal pain in fewer body regions.^62,69 If we look at support over time, high work social support in midlife decreased the risk of health-related exit and unemployment. ⁷³ Thus, social support in the workplace can promote health among workers. ⁷⁴

Need for future studies

While the work-family conflict and health literature are expanding, it is still heavily reliant on cross-sectional research designs particularly among women. ⁷⁵ A limitation of this area of literature is the lack of a standard definition of “responsibilities.” A more standardized definition of “responsibilities” could include more comprehensive measures with questions about tasks outside the house (for example, grass mowing and snow clearing), taking care of a person with a loss of autonomy, family budget, car maintenance, and playtime with children. ⁷⁵ Future research should explore the longitudinal health effects on working women.

Despite promising evidence for social support at work, more analysis is needed to fully understand the effects. The benefit of social support may not provide equal benefit, and some groups may even struggle due to the intensity of their social connections and perception of inclusion at work. Further studies are needed to focus on uncovering which function(s) or mechanism(s) of social support are actually beneficial among hard-to-reach and precarious workers who are dealing with enormous life challenges. ⁷⁶

Perceived discrimination in the workplace

Perceived discrimination refers to an individual's perception of negative attitude, judgment, or unfair treatment due to specific characteristics such as gender, race, ethnicity, and social status. ⁷⁷ Despite the intent of the victim, the perception of discrimination still causes stress and deleterious behaviors for an individual. Short- and long-term health outcomes stemming from workplace discrimination are similar to those originating from non-work discrimination.^14,78–80 Mounting evidence has demonstrated a role of psychosocial stressors such as discrimination in hypertension and cardiovascular disease. ⁸¹ The negative impacts of discrimination in the workplace can be both short-term (increasing stress levels, blood pressure and other physiological symptoms) and long-term (leading to musculoskeletal problems, arthritis, heart disease and other physical illnesses). ⁷⁹ Recent research indicates a potential association between workplace violence (Work­place violence was determined based on self-reported threats, bullying, or harassment at work over the past 12 months, supplemented with additional information regarding frequency) and an increased risk of CVD, which included all forms of heart disease and stroke in the working-age population. ⁸² Workplace discrimination in particular is also associated with lower overall health and more chronic illness. ⁷⁹ However, individuals with high perceived control were less negatively affected by workplace discrimination when reporting on their overall health. ⁷⁹ Although racial composition of workplace may be a mechanism by which high SES increases discriminatory experiences for African Americans, males and females may not differ in this regard.^17,19

Acute work-related stress and chronic disease

A working environment can damage health not only through obvious physical hazards, but also through stress. The last couple of decades have seen marked increases in scientific knowledge about causal pathways and physiological mechanisms that help explain the links between social and economic factors and health. ²⁴ Examples include physiologic damage to multiple vital organ systems caused by chronic stress through neuroendocrine and immune pathways.^83–86 Stressful experiences, including aspects of the work environment and working conditions, can trigger the release of hormones and other substances in the body which, particularly with stressors over time, can damage immune defenses and vital organs.^87,88 This physiologic chain of events can result in more rapid onset and progression of chronic illnesses including cardiovascular disease; the bodily wear and tear associated with chronic stress may accelerate ageing.^87,89,90 In addition, work stressors can cause depression and other mental health episodes, ⁹¹ and strain from trying to cope with daily events may over time, lead to far more physiological damage than a single stressful event, even if the event is dramatic. Daily hassles can include constant challenges posed by work environments in which a person may feel disrespected, experience microaggressions at work, ⁹² and feel intimidated or under constant strain trying to balance the demands of work and family responsibilities with inadequate resources and support.

Need for future studies

There is a well-documented association between experienced discrimination and negative psychological symptoms.^11,12 However, research has yet to examine whether there is an interaction between race/ethnicity and how the experience of racial discrimination in the workplace moderates an association between discrimination experiences and depression or other negative emotions due to treatment based on race. ¹⁴ As such, more research is needed which addresses these issues of equity and inclusion in the workplace. Additionally, it is recommended that research be carried out at short time intervals in order to catch all new cases of depressive and other mental health episodes, and that the study designs clearly accommodate the need to distinguish first-onset from recurrent depressive episodes. ⁹¹

Workplace exposures on epigenetics

Health lies at the intersection of the environment and the individual. The genetic makeup of the individual has long been understood to impact health, with numerous polymorphisms contributing, usually each in small ways, to how a person responds to environmental stimuli. More recently, we have come to understand that the converse is also true, in that the environment can shape the epigenome, which in turn influences gene expression in response to the environment. Epigenetic modifications of the DNA, such as opening or closing of chromatin structures mediated by histone modification, and the direct modification of the DNA itself by methylation. DNA methylation, often at C-G rich areas known as CpG islands in the promoters of genes, contributes to gene regulation.

Occupation has been shown many times to influence DNA methylation, both at specific sites and in a more gross manner. Occupational exposures that impact DNA methylation include benzene,^93–95 nanoparticles, ⁹⁶ radiation,^97–99 pesticides,^100–104 chromate,^105–107 nickel,^108,109 lead, ¹¹⁰ mercury, ¹¹¹ per- and polyfluoroalkyl substances, ¹¹² and welding fumes. ¹¹³ Even exposures such as noise have been linked to changes in DNA methylation patterns. ¹¹⁴ Exposure to these various insults varies in ways besides occupation, such as with neighborhood and socioeconomic status.^114,115 Epigenetic modification of DNA is one of the proposed “hallmarks of environmental insults”. ¹¹⁶ DNA modification, in turn, impacts cardiac health ¹¹⁷ as well as mental health. Differential methylation has been described in depression, ¹¹⁸ stress resilience, ¹¹⁹ and “burnout”. ¹²⁰ Recently, a comprehensive study looked at the effects of socioeconomic factors on biological ageing as measured by eight different molecular clocks based on patterns of DNA methylation. ¹²¹ Biological ageing, as measured by DNA methylation, was only partially explained by smoking, alcohol consumption, and obesity, leaving the socioeconomic status index as a significant influence on ageing.

Epigenetic modification potentially impacts cardiovascular health. Biological age, as determined by DNA methylation-based clocks, is correlated with cardiovascular disease incidence. Using a DNA methylation-based clock, every one-year increase in biological age was found to increase the risk of cardiovascular disease by 4%. ¹²² Furthermore, studies have shown differential DNA methylation in atherosclerosis. ¹²³ Recently, a study utilizing an NHANES cohort and a DNA methylation-based method showed better performance as a measure of CVD risk than a PCR-based measure of telomere length. ¹²⁴ As methylation changes with age and exposures, there is the potential for cardiovascular risk factors to mediate their effects through these epigenetic changes. While DNA methylation correlates to cardiovascular disease risk by virtue of measuring biological ageing, there remains the possibility that workplace exposures can more directly affect risk, although this has not often been explicitly explored. As one example, nightshift work has been shown to increase the risk of atherosclerosis. ¹²⁵ Nightshift work, in a separate study, also showed “suggestive” correlations to differential methylation patterns. ¹²⁶ Clearly, the relationship between work and cardiovascular disease risk, as mediated by epigenetics, remains an area open to further exploration.

Telomere length

Telomere length serves as another molecular clock. These nucleoprotein complexes serve as the aglets of chromosomes, protecting against the slow erosion that takes place due to the end-replication problem of linear chromosomes. The very ends of chromosomes lose some genetic material at each replication, and thus these repetitive elements have evolved to prevent the erosion of coding DNA. This erosion, and the rate of erosion, can serve as a molecular clock of biological ageing.

Interestingly, several studies have demonstrated an acceleration of telomere erosion in response to social determinants of health (SDOH). Childhood adversity has been associated with shorter telomere length in adults. ¹²² The socioeconomic status of parents even impacted the telomere length of their children. ¹²³ Lifestyle choices also impact telomere length. ¹²⁴ Similar to DNA methylation, numerous occupational exposures and the nature of work (such as shift work) have been shown to be associated with reduced telomere length.^{102,125–141} Biological ageing, as measured by telomere attrition, was accelerated in a longitudinal study in neighborhoods with lower socioeconomic status or worse social environment. ¹⁴² Furthermore, vascular ageing has been shown to correlate with telomere length. ¹⁴³ Vascular injuries have similarly been associated with decreased telomere length. ¹⁴⁴ One study found that increased telomere length was associated with workplace learning opportunities. ¹⁴⁵ Another study showed a marginal association between maternal stress (including socioeconomic stressors) and shorter telomeres in infants. ¹⁴⁶ Interestingly, a 2016 metanalysis indicated that mindfulness exercises were associated with increased telomere length, perhaps serving as an occupational therapy intervention. ¹⁴⁷ One study of cardiovascular disease risk in the U.S. examined telomere length in a relatively large sample (963 subjects) ¹⁴⁸ ; and found one social factor—home ownership associated with longer telomere length in general, with some differences in significance among ethnic or racial sub-populations. Interestingly, a study of women in the southern U.S. showed that while “chronic stress” led to shorter telomeres, however “perceived stress” may buffer this effect. ¹⁴⁸

MicroRNA molecules

A third genetic influence on gene expression is the presence of microRNA molecules. These sometimes are categorized under epigenetic influences because they are thought to impact phenotype solely through controlling the expression of other genes. MicroRNA are 22 nucleotide RNA molecules. Interacting with cognate sequences largely in the 3’ untranslated regions of mRNA molecules, they can either block translation by the ribosome or create double-stranded RNA regions that flag the mRNA for degradation. MicroRNA are encoded by their own genes, similar to mRNA, which puts their expression properly under the field of transcriptomics rather than epigenetics. However, their stability even in peripheral circulation and their changes in response to numerous stimuli gives them great utility as biomarkers.

Several studies have assayed microRNAs as biomarkers of occupational exposures. A pair of 2019 reviews^148,149 summarize literature on microRNA expression changes in response to occupational exposures. Exposures to particulate matter, metals, and polycyclic aromatic hydrocarbons have been demonstrated to result in significant changes in the expression of specific circulating microRNAs, although on the whole there are no reliable biomarkers of these exposures. This is largely blamed on the heterogeneity of both exposures and study designs. More recently, Sturchio et al. reviewed the use of microRNAs as biomarkers for the diagnosis and prognosis of mesothelioma, ¹⁵⁰ a cancer directly related to occupational and social exposure to asbestos. MicroRNA has been proposed as biomarkers for diverse occupational exposures, including mercury, ¹⁵¹ carbon nanotubes, ¹⁵² volatile organic compounds, ¹⁵³ and even noise. ¹⁵⁴ Because microRNAs function through the regulation of other genes, their expression and how it changes between conditions may additionally inform etiology. However, this picture is often obscured by the ability of each microRNA to recognize and regulate many targets mRNA, impacting potentially several cellular pathways.

With specific regards to musculoskeletal and cardiac health, much less is known about the role of microRNAs as biomarkers or mediators of disease. One study showed that miR-143 and miR-145 were both significantly higher in patients with essential hypertension than in age- and gender-matched control patients. ¹⁵⁵ Our own recent study further identified changes in microRNA expression associated with lower back function and motion sickness. ¹⁵⁶

Need for future studies

Clinical translation of epigenetic biomarker data is complicated by several factors. For one, studies are generally limited in size and difficult to generalize. Differences in the way analyses are performed, such as by RT-PCR or microarray or next generation sequencing, result in data that are not immediately comparable. Additionally, studies assay different biological tissues, such as saliva, tissue, or blood. Variability in sample types, collection methods, nucleic acid isolation methods, assay types, and data analyses all remain standardized. If these challenges can be overcome, then epigenetic biomarkers offer easy-to-assay biomarkers that can potentially inform us about a plethora of exposures, benefiting public health.