Pratyaksh K. Srivastava1
1Harvard Medical School, Boston, MA, USA
Address correspondence to: Pratyaksh_Srivastava@hms.harvard.edu
Coronary Artery Disease (CAD) is the leading cause of death and disability in the United States, accounting for 1 in every 6 deaths [1,2]. In 2010, the disease cost the U.S. almost $109 billion in medications, health services, and loss of productivity , making it an important consideration for national health policy. In considering the health issues related to the disease, it is helpful to examine the root causes of CAD, which can be broken down into a genetic component (40-60%) and an environmental component [4,5,6]. Of the environmental causes, socioeconomic status (SES) has proven an especially powerful and curious factor . This paper will look at the impact of SES on CAD development and perpetuation. It will focus on the interplay between SES, stress, and CAD, and provide policy recommendations for the future.
Michael Marmot’s Whitehall Studies provided the first hint that SES influenced CAD. Whitehall I looked at 17,530 London Civil Servants ranging in age from 40-64 . Marmot found that the age-adjusted prevalence of angina was 53% higher and ischemic electrocardiographic abnormalities were 77% higher in those who were in the lowest employment grade compared to those who were in the highest . Further, at 7.5 year follow up, the coronary mortality was almost 4 times greater in the lowest employment grade compared to the highest . Whitehall II expanded this study to females and found similar patterns . The difference in cardiovascular problems and deaths was initially thought to be due to the difference in coronary risk factors between the two groups: those in the lowest grade smoked more, exercised less, were more overweight, shorter, and had increased prevalence of hypertension . However, even after Marmot adjusted for these factors, the cardiovascular differences between the two groups remained significant . Marmot concluded at the time that one’s employment status was more accurate at predicting his chance of dying from CAD than any of the known common risk factors .
Why was this? One proposed idea was that those of lower SES were faced with greater stress, both at home and at work . One group, using the Whitehall II cohort, looked at free salivary cortisol levels in individuals both when they woke up and thirty minutes after as a marker for stress levels. Cortisol levels immediately after waking up did not differ between those of different SES on workdays or weekends . When measured thirty minutes after awakening, however, those of lower SES had higher cortisol levels than those of higher SES, and this effect was observed on both workdays and weekends . Other sources have also documented greater stress in those of lower SES .
The term allostatic load has been used to describe the wear on the body that results from continuous or prolonged activation of the body’s stress system [9,10,11]. Normal exposure to stress, including elevated heart rate and blood pressure, is not detrimental and may even be protective . Constitutive activation of these pathways, however, overwhelms the system and results in detrimental effects . One example is a decreased ability to recover from stressful situations . So, for those of low SES, not only is the body exposed to stressors more constantly and for greater periods of time, it also possesses a reduced ability to recover from the stress .
There have been various other biological mechanisms proposed for how stress ultimately leads to CAD development. Some groups have noted that those of lower SES have higher levels of plasma fibrinogen, which is associated with an increased risk of CAD . Others have implicated the pro-inflammatory cytokine IL-6, which also plays a role in CAD development, and is elevated in response to psychological stress . Others still have looked at the effect of chronic stress during developmental windows in childhood .
Stress during childhood offers an interesting perspective into potential environmental contributors to CAD development. For the majority of the 20th century it was thought that cardiovascular conditions such as stroke and CAD were mainly influenced by adult lifestyle and behavior . More recent trends, however, show that environmental factors during childhood strongly influence adult disease outcomes . For example, childhood respiratory illness correlates with adult lung disease, and nutritional defects during the prenatal period are associated with greater incidence of cardiovascular disease later in life . Recent studies have also shown that adults with a history of depression and mistreatment during early childhood are almost two times as likely to possess elevated C reactive protein levels .
What is the root of all this stress? There are a few obvious answers: those of low SES are more likely to live in areas of greater population density, crime, and noise pollution. In addition, they frequently have limited access to resources such as healthy supermarkets, restaurants and health services . These are plausible, yet somewhat downstream explanations.
Marmot offers a possible root. He proposes that poverty results when an individual cannot meet the fundamental needs of autonomy and empowerment . So under this framework, those of lower SES feel greater stress because of a lack of control and empowerment in their lives, and it is this increased stress that puts them at greater risk for CAD . A study in the Netherlands displayed that an individual’s perception of decreased control in his/her life was correlated with increased CAD . In Whitehall II, Marmot asked women about how much control they felt they had in the home and those who reported less control possessed higher risks of CAD . Finally, in the Czech Republic, those who reported lower control at work had higher risk of myocardial infarction . Marmot suggests two ways in which individuals of low SES feel disempowered and helpless: stress caused by amount of control in relation to demand and stress originating from an imbalance between efforts and rewards .
Some may argue that those occupying jobs that allow them to maintain a high SES have more stressful demands placed on their time . As Marmot points out, it is not necessarily the quantity of stressful demand but rather how much control is afforded in comparison to that demand . So while a banker or physician may work 100 hours/week, they are in control of many aspects of their lives. Their high SES affords them the ability to choose where to live, where they eat, and where to partake in recreational activities and consequently there is little to no imbalance between efforts and rewards. Those of lower SES may also work 100 hours/week but are usually in positions where comparatively less control is afforded , and due to lower compensations, this extends to the home environment as well. These individuals are often told what to do and are under perpetual and strict scrutiny. When these individuals return home after work, they are often traveling to areas that they may not want to live in, that are polluted with noise and crime, and that frequently offer no healthy grocery stores, restaurants, or recreational facilities. There is a grave imbalance between efforts and rewards as hard work in this circumstance is much harder to translate into upward social mobility and a sense of autonomy and empowerment. These individuals are less likely to have, as Marmot puts it, “a reason to lead lives they have reason to value.” 
How can policy be tailored to solve issues of lack of autonomy and empowerment? The first place to intervene is during childhood. As the studies above display, chronic stress during times of development has been implicated in increasing one’s chance of not only CAD, but of various other ailments as well. Childhood is also a time when it is easy for individuals to feel out of control, especially when compounded by the stress effects of poverty.
There are a few interventions that could help empower children of low SES. The first is to improve access to quality education and extracurricular programs. In quality schools, the child is usually surrounded by supportive peers and instructors and is removed from the stresses that may be waiting at home or in the outside environment. Many schools in low SES areas are of poor quality, have high dropout rates, and are inundated with drug and criminal activity. One solution to improving access to quality education and moving towards empowering children and reducing stressors may be a widespread implementation of charter schools.
Charter schools receive public funding but are exempt from many of the rules and regulations that govern normal public schools . This important point allows these schools to reallocate resources from maintaining a public school bureaucracy towards building networks that place special emphasis on academic achievement and the creation of safe zones . Students gain further autonomy by being able to choose their school instead of being placed in a random, poorly structured public school that may be difficult to access. . Charter schools have been widely successful throughout the nation, and in 2012, Chicago’s charter schools held the top 9 spots out of all Chicago high schools for ACT scores. 
Year-round charter schools also pose an interesting solution to the problem. Research has shown that the education gap between those of high and low SES starts very early on . Specifically, the gap seems to manifest itself during the summer months of elementary school where those of higher SES are afforded greater access to resources . Year-round schooling may serve as an equalizer of sorts by hindering the formation and perpetuation of the education gap.
Another intervention could be greater access to primary care for children. Children of lower SES have poorer mental health and carry a higher stress burden than those of higher SES . Access to a primary care physician may help these children cope with mental health issues and possibly ameliorate some of their stress burden. The less stress burden carried forward, the better health outcomes later in life . Frequent contact with a primary care physician could also help bring to light cases in which the child’s environment, school or home, is unsafe.
Adults pose a much more difficult problem. Taking Marmot’s analysis into consideration, a large source of stress comes from personal feelings of lack of autonomy and disempowerment. Improving these feelings in those of low SES would require adjustments to the job and home environment.
To improve the job environment, there needs to be changes that empower the worker and that offer better rewards for his/her efforts. Possible solutions include greater wages, greater governmental support and/or better work health insurance coverage. Employee reward programs that focus on promoting employee autonomy and self worth, and on creating a perfectly transparent promotional system would further lessen stress in the work environment. A system defined by an ambiguous correlation between efforts and achievement leaves individuals feeling as if they have no control over their own upward mobility. Having concrete goals to work toward and knowing exactly what steps are required for promotion incentivizes individuals to pursue longitudinal job experiences, and creates a better sense of community and stability in the workplace.
The home environment is more difficult to change since SES often dictates where an individual has to live, which subsequently influences what he/she has to eat and the types of recreational opportunities that are available. One possible way to improve low SES neighborhoods is to empower and motivate residents to change and improve their own community. Mobilizing the youth could prove especially fruitful. These projects could range from educational campaigns on the merits of healthy eating to park and home restorations. Other examples include having skills workshops for community members or holding fundraisers for community development projects. If individuals in the community are involved in the improvement and change around them, they will feel a greater sense of ownership and attachment to their community, and ultimately a greater feeling of empowerment and autonomy.
Low SES, by influencing stress levels, has clear biological and social links to CAD. Providing children with a quality education, healthy places to eat, and a safe environment has the potential to help them escape the low SES poverty trap, and to improve their health status. For adults, worker reform, initiatives that promote transparency, and the establishment of communities individuals feel connected to and empowered by are potential ways to reduce environmental stressors. The ultimate goal is stress reduction through empowerment and autonomy—a goal with the potential to have widespread implications for CAD prevention.
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