Jennifer Harris, MD
Health disparities have emerged as one of the great challenges to our health care system and a critical concern for the health of our U.S. population. Among the most dramatic disparities are seen in cardiovascular disease (CVD). Disparities in stroke outcomes are also widely reported in the literature. Whereas stroke rates in the U.S. have declined over the last decades, stroke mortality rates in nonwhites (predominantly Non-Hispanic (NH) Blacks) have remained substantially higher than in NH Whites . This disparity may be due to differences in stroke incidence, with relative risk=2.77 (95%CI 1.37-5.62) between NH blacks and NH whites among those <55 years of age and 2.23 (95%CI 1.66-3.00) in those >55 years of age . Data from the REasons for Geographic And Racial Differences in Stroke (REGARDS) study suggest that the prevalence of stroke risk factors, particularly hypertension and diabetes, while clearly higher among NH Blacks, account for only 40% of the Black-White disparities in stroke incidence. The reasons for the remaining 60% are elusive .
Various socioeconomic determinants of health have been shown to predispose patients to developing CVD and stroke. According to national health disparities data for cardiovascular disease outcomes, there are several social determinants of health (SDOH) that may help explain stroke disparities. SDOH are defined as economic and social conditions that influence individual and group differences in health status. SDOH include low education, low income, living in an impoverished area, social isolation, and lacking health insurance, among others. To further investigate the association between incident stroke and SDOH, Reshetnyak et al. analyzed data from the REGARDS study to determine the individual and cumulative effect of SDOH on incident stroke.
The REGARDS study is a national, representative, prospective cohort of black and white adults aged 45 years and older, living across the 48 continental U.S. states and D.C. and recruited from 2003-2007. The primary outcome was defined as clinically adjudicated incident strokes, which was defined as: 1) focal deficits lasting over 24 hours and confirmed via medical record, 2) clinical strokes confirmed with imaging, and 3) expert adjudicated stroke deaths. For the primary exposure, 10 candidate SDOH were included, which consisted of education, income, zip code poverty, residence in health professional shortage areas, residence in the worst ranked states for public health infrastructure, lack of health insurance, rural residence, social isolation, and black race.
The study population included 27,813 participants, and the mean age was 64.7 years at baseline. 55.4% were women, and 40.4% were Blacks. Separated by age, the younger cohort (<75 years) included 83.4% of participants. Of these, 55.9% were women, and 41.6% were Blacks. The older cohort (≥75years) included 52.6% women and 34.7% Blacks. Over a median follow up of 9.5 years, 1470 incident stroke events were observed. Stroke incidence was lower in the younger cohort (<75 years), compared to the older cohort (³75 years). Out of the 10 candidate SDOH, seven were associated with stroke (p<0.10). Those included race, education, income, zip code poverty, health insurance, social isolation, and residence in one of the 10 lowest ranked states for public health infrastructure. In the younger cohort, the incidence of stroke increased with each additional SDOH. Stroke incidence was 2 times larger for individuals with >3 SDOH compared to those without SDOH. In the older cohort, the incidence of stroke was 1.3 times higher for individuals with>3 SDOH compared with those with no SDOH. The absolute difference in stroke incidence between individuals without SDOH vs. those with>3 SDOH was 3.42 per 1000 person-years for the younger group and 3.72 for the older group.
In both age strata, individuals with a greater number of SDOH were more likely to be black women, have low annual income, live in an impoverished neighborhood, and reside in states with poor public health infrastructure. Individuals with a greater number of SDOH were more likely to have a history of hypertension or diabetes, taking antihypertensive medications and insulin.
Although, in fully adjusted cox models, observed effects from the minimally adjusted models were attenuated across both age groups, the upward risk trend persisted among those <75 years of age (p for trend<0.001). Such as that compared to having no SDOH, having 1 SDOH was associated with an adjusted HR of 1.26 (95%CI1.02-1.55), 2 SDOH were associated with a HR of 1.38 (95%CI1.12-1.71), and >3 SDOH were associated with a HR of 1.51 (95%CI1.211.89). In the older cohort, none of the observed effects reached statistical significance.
The results of this study contribute to the existing and growing knowledge of health disparities in stroke by showing how the combined burden of SDOH within the same individual significantly increases risk of stroke for individuals younger than 75. Even after controlling for potential confounders, stroke risk remained 50% higher among those with 3 or more SDOH compared to those without any SDOH in this group.
With the enormous advances in knowledge that have occurred in the past couple decades, there is no doubt that social factors are powerful determinants of health. There is increasing evidence that supports causal relationships between many social factors and health outcomes. For instance, the availability of alcohol in disadvantaged neighborhoods can influence its use among young people. Similarly, a higher concentration of convenience stores has been linked to tobacco use, and lower availability of fresh produce, combined with concentrated fast-food outlets and few recreational opportunities, can lead to poorer nutrition and less physical activity, which can, in turn, lead to chronic disease and stroke.
Because SDOH are considered outside the realm of standard medical care, we as physicians often do not take them into consideration. We undergo intensive training in medicine but receive little to no training in the social aspect of medicine. However, every healthcare professional, at a minimum, should be aware of the social factors that influence health-related behaviors. As clinicians, we can be a key resource for local, state, and national policy makers on the crucial issue of health equity for all.
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- Howard G, Cushman M, Kissela BM, et al. Traditional risk factors as the underlying cause of racial disparities in stroke: lessons from the half-full (empty?) glass. Stroke. 2011;42:3369-75.