Social factors, such as socioeconomic status and exposure to violence, and psychological factors, such as depression, stress and anxiety, have been associated with asthma [10
]. Exposure to both social and psychological risk factors varies by race, ethnicity and social class. One study demonstrated that Puerto Ricans who self-identify as black have lower mean household income and are more likely to live below the poverty level than those who self-identify as white [68
]. In addition, racial reporting was a significant predictor of hourly wages for Puerto Rican men in New York City, even after adjusting for potential confounding factors [69
]. Similarly, among Mexican Americans those with dark skin and American Indian-physical appearance are more likely to be discriminated against, receive less education and hold occupations with lower prestige than their light skin and European-appearing counterparts [70
]. This relationship was also observed with respect to earnings [71
]. Thus, asthma researchers cannot ignore social and psychological factors that vary by race, ethnicity and social class.
There is a complex interplay between race and ethnicity and socioeconomic status with respect to asthma-associated risk factors. Togias et al.
demonstrated that socioeconomic status influences allergy in African Americans: African Americans in the lowest income quartile had higher rates of cockroach sensitization than African Americans in higher income brackets. In contrast, there was no association between cockroach sensitization and income level among European Americans [72
]. In addition, our group recently demonstrated that ancestry interacts with SES to modify the risk of asthma [2
]. In Puerto Rican asthmatics of low SES, higher European ancestry was associated with asthma, whereas in Puerto Rican asthmatics of high SES, higher African ancestry was associated with asthma () [2
]. In this example, ancestry and SES, which may be surrogates for other biological, social, psychological or environmental factors, interact to influence asthma risk. These studies underscore the complex nature of class-specific environmental exposures, which are known risk factors for asthma and allergy.
Percent African ancestry in Puerto Rican asthma cases and controls stratified by socioeconomic status (SES). SES was obtained using clinic recruitment site address.
Social and psychological risk factors are closely related because social factors can increase psychological stress. Psychological factors may alter a person’s allostatic load, the physiological sequelae of chronic exposure to stress. Although the exact processes are unclear, the pathophysiologic sequelae are thought to be mediated through neuroendocrine and/or immunologic pathways [73
]. The influence of allostatic load on disease outcomes has been demonstrated for coronary heart disease (CHD). For example, the Whitehall study demonstrated that the risk of CHD increased as social class decreased among classes of British civil servants. CHD in the lowest social class of British civil servants was 3-fold higher compared to the highest class, after adjusting for known CHD risk factors [74
]. In addition, British civil servants who experienced negative interactions in their closest relationship, such as conflict in their marriage, were more likely to develop CHD than those who did not, even after adjusting for differences in demographic, social, biological and psychological confounders [75
]. Racial discrimination can also influence health outcomes by increasing allostatic load. In African Americans, perceived racial discrimination was associated with risk of hypertension, carotid plaque and low-birth-weight deliveries [76
]. Chronic psychological stress, which may be exacerbated by social class or perceived discrimination, can “get under your skin” and alter health outcomes. However, the mechanism by which both social and psychological risk factors influence physiological processes is unclear.
Recently, Chen and colleagues investigated the mechanism by which neighborhood and family level social and psychological factors influence asthma [77
]. They found that lower levels of family support affected asthma symptoms and pulmonary function through biological pathways, such as allergic inflammation, whereas community factors influenced asthma symptoms through behavioral pathways, such as higher smoking rates. Although the population in this study was mixed and mostly of European descent, it provides an excellent basis for the examination of the influence of social factors and changes in allostatic load on disease. Genetic, environmental, social and psychological risk factors likely operate at the individual, family and community level. However, further research on biopsychosocial models of asthma and other complex diseases is needed. Research across a broad range of populations will refine the mechanisms through which these risk factors interact and translate into disparities in disease outcomes.