insights

                                                                                                                                                                                            Read time 5 minutes

An immune system with healthy reactivity and resilience is significant for fighting infections, preventing diseases, and achieving overall mental and physical health. For underserved populations, health inequities, including affordability, accessibility, and social determinants of health, sustain barriers to optimal health care and may present challenges in the development of robust immune resilience.^1-3 Consideration of such factors and understanding healthcare system disparities that are beyond a patient’s control helps to develop personalized treatment plans while promoting patient empowerment and a collaborative patient-practitioner relationship.

Immune Fitness: Potential Barriers in Underserved Populations

A 2019 meta-analysis of 35 studies found that compared to higher socioeconomic status (SES), low SES exposure in childhood and adolescence increased levels of inflammation in adulthood (measured by C-reactive protein, IL-6, and fibrinogen).⁴ Another meta-analysis of 15 studies (n=43,629) also suggests an inverse association between childhood SES and adulthood inflammation, with participants from the least advantaged families measuring 25% higher in C-reactive protein levels.⁵ What other environmental and social factors may impact immune system responses? Healthy food access, exposure to pollutants, and chronic stress are a few factors that have been studied in relation to both immune system function and prevalence within underserved communities.

Nutrition & a Healthy gut

Adequate and uninterrupted access to healthy and varied foods is essential for positive health outcomes. Dietary patterns that include anti-inflammatory foods such as fruits and vegetables supply nutrients and natural antioxidants that may contribute to a more robust immune system through reducing inflammation and oxidative stress.^6,7 However, reliable access to affordable, nutritious foods can be a potential challenge for immune health in underserved populations. Data from 2021 suggested that 10.5% of all US households experienced food insecurity at least some of the time during that year while 32.1% of households with incomes below the federal poverty line experienced food insecurity.⁸ Further, results from a cross-sectional study of over 10,000 participants suggested that food security status may be associated with a dietary inflammatory potential.³ Specifically, those with low or very low food security reported a lower intake of several anti-inflammatory foods and nutrients compared to those with greater food security, including fiber, vitamins A, B6, C, and E, β-carotene, and magnesium.³

Accessibility and consumption of varied and healthy foods also influences gut microbiome function, a key regulator of immune system homeostasis. Communication between the microbiome and the intestinal mucosal immune system impacts immune response,⁹ and dysbiosis may contribute to blunted immune reactivity.¹⁰ In addition to nutrition-based studies, microbioscape research, which combines microbiome science and landscape research,¹¹ suggests microbial input from the environment also influences immunoregulation pathways.¹² Accessibility to green spaces, for example, has been shown to benefit health and lower all-cause mortality risk,¹³ yet studies indicate that access to urban green spaces within under-resourced US neighborhoods is limited.^14,15

Exposure TO POLLutants

Ambient pollutants and toxicants such as heavy metals, pesticides, and other endocrine-disrupting chemicals have been associated with immune system imbalances,^2,16,17 and disproportionate exposure levels have been documented for underserved populations in the US.^18,19 A 2020 assessment by the Environmental Protection Agency indicated that unsafe air quality (with the highest fine particulate matter [PM2.5] concentrations) was most often recorded in low-income populations that included larger percentages of Black, Indigenous, and People of Color (BIPOC) communities.²⁰ The American Lung Association has echoed concern for environmental exposure inequality, indicating that within Medicaid and Medicare populations, lower SES and BIPOC communities have experienced an increased risk of death from fine particle pollution.²¹

Chronic exposure to pollutants and toxicants may lead to an overloaded body burden, increased systemic inflammation, and clinical manifestations of immune dysfunction. A 2020 review reported common themes among cell and animal model studies that investigated the mechanistic effects of air pollutants on different immune cells.¹⁷ Ambient pollutants were found to directly activate cellular signaling pathways, triggering inflammatory cytokine release from the epithelium and macrophages. In addition, the pollution particulates enhanced TH lymphocyte 2 and 17 responses.¹⁷ 

CHRONIC Stress

Underserved populations that encounter access barriers through social determinants of health disproportionately experience psychosocial stress. According to a 2020 report by the Centers for Disease Control and Prevention, employment-related worries, limited access to health care, food insecurity, and housing instability may compound the already elevated risk of chronic stress in BIPOC communities.²² Experiencing stress can activate inflammatory responses, with acute stressors potentially enhancing immune response and chronic stressors ultimately suppressing immune function.^1,23 A 2019 systematic review and meta-analysis of 75 studies explored this stress-immune relationship further by evaluating the effectiveness of stress-reducing psychological interventions on the activation of immune responses.²⁴ After the specific intervention (i.e., stress management, relaxation, meditation, mindfulness, cognitive-behavior technique, or counseling), immune-related outcomes were measured either through in-vitro, in-vivo, or psychophysiological challenges (i.e., natural killer cell and cytokine responses, wound healing and skin testing, or speech tasks and treadmill exercise test). Overall, a small to medium effect size was suggested for all interventions, with those studies measured through in-vitro stimulations and psychophysiological challenges showing more optimal immune responses.²⁴

Clinical Considerations

Immune system function is optimized by a range of factors, from a healthy diet and a balanced gut microbiome to chronic stress and toxicant exposures. Racial, economic, social, and cultural barriers create immune resilience challenges within underserved populations, illustrated through the disproportionate impact of chronic and infectious diseases in these communities.²⁵ The barriers and social determinants of health are antecedents and mediators of physiological dysfunction in the functional medicine matrix model. They are important factors when considering immune health strategies and when determining what lifestyle practices are modifiable for a patient.

Meeting a patient where they are, understanding access barriers, and recognizing social conditions that may be beyond their immediate control are all part of a patient-empowered collaborative relationship. These considerations ultimately help to provide the most effective personalized intervention that supports optimal immune health. Learn more about immune reactivity and boosting resilience from functional medicine experts at IFM’s Immune Advanced Practice Module (APM).

Related Articles & Podcasts

Supporting Health in Underserved Populations

Food Insecurity and Chronic Disease

Chronic Stressors, Disease Burden, and Sustainable Lifestyle Interventions

Neighborhood Health: Pollutant Exposures and Chronic Disease Risk

References

1. Segerstrom SC, Miller GE. Psychological stress and the human immune system: a meta-analytic study of 30 years of inquiry. Psychol Bull. 2004;130(4):601-630. doi:1037/0033-2909.130.4.601
2. Nowak K, Jablonska E, Ratajczak-Wrona W. Immunomodulatory effects of synthetic endocrine disrupting chemicals on the development and functions of human immune cells. Environ Int. 2019;125:350-364. doi:1016/j.envint.2019.01.078
3. Bergmans RS, Palta M, Robert SA, Berger LM, Ehrenthal DB, Malecki KM. Associations between food security status and dietary inflammatory potential within lower-income adults from the United States National Health and Nutrition Examination Survey, cycles 2007 to 2014. J Acad Nutr Diet. 2018;118(6):994-1005. doi:1016/j.jand.2017.12.003
4. Milaniak I, Jaffee SR. Childhood socioeconomic status and inflammation: a systematic review and meta-analysis. Brain Behav Immun. 2019;78:161-176. doi:1016/j.bbi.2019.01.018
5. Liu RS, Aiello AE, Mensah FK, et al. Socioeconomic status in childhood and C reactive protein in adulthood: a systematic review and meta-analysis. J Epidemiol Community Health. 2017;71(8):817-826. doi:1136/jech-2016-208646
6. Iddir M, Brito A, Dingeo G, et al. Strengthening the immune system and reducing inflammation and oxidative stress through diet and nutrition: considerations during the COVID-19 crisis. Nutrients. 2020;12(6):1562. doi:3390/nu12061562
7. Childs CE, Calder PC, Miles EA. Diet and immune function. Nutrients. 2019;11(8):1933. doi:3390/nu11081933
8. USDA Economic Research Service. Food security and nutrition assistance. US Department of Agriculture. Updated October 18, 2022. Accessed November 22, 2022. https://www.ers.usda.gov/data-products/ag-and-food-statistics-charting-the-essentials/food-security-and-nutrition-assistance/#:~:text=Food%20insecurity%20was%20lower%20in,2011%20and%20has%20declined%20since
9. Fung TC. The microbiota-immune axis as a central mediator of gut-brain communication. Neurobiol Dis. 2020;136:104714. doi:1016/j.nbd.2019.104714
10.  Brzozowski B, Mazur-Bialy A, Pajdo R, et al. Mechanisms by which stress affects the experimental and clinical inflammatory bowel disease (IBD): role of brain-gut axis. Curr Neuropharmacol. 2016;14(8):892-900. doi:2174/1570159X14666160404124127
11.  Robinson JM, Jorgensen A. Rekindling old friendships in new landscapes: the environment–microbiome–health axis in the realms of landscape research. People Nat. 2020;2(2):339-349. doi:1002/pan3.10082
12.  Rook GA. Regulation of the immune system by biodiversity from the natural environment: an ecosystem service essential to health. Proc Natl Acad Sci U S A. 2013;110(46):18360-18367. doi:1073/pnas.1313731110
13.  Rojas-Rueda D, Nieuwenhuijsen MJ, Gascon M, Perez-Leon D, Mudu P. Green spaces and mortality: a systematic review and meta-analysis of cohort studies. Lancet Planet Health. 2019;3(11):E469-E477. doi:1016/S2542-5196(19)30215-3
14.  Wen M, Zhang X, Harris CD, Holt JB, Croft JB. Spatial disparities in the distribution of parks and green spaces in the USA. Ann Behav Med. 2013;45(Suppl 1):S18-S27. doi:1007/s12160-012-9426-x
15.  Jennings V, Floyd M, Shanahan D, Coutts C, Sinykin A. Emerging issues in urban ecology: implications for research, social justice, human health, and well-being. Popul Environ. 2017;39(1):69-86. doi:1007/s11111-017-0276-0
16.  Mokarizadeh A, Faryabi MR, Rezvanfar MA, Abdollahi M. A comprehensive review of pesticides and the immune dysregulation: mechanisms, evidence and consequences. Toxicol Mech Methods. 2015;25(4):258-278. doi:3109/15376516.2015.1020182
17.  Glencross DA, Ho T-R, Camiña N, Hawrylowicz CM, Pfeffer PE. Air pollution and its effects on the immune system. Free Radic Biol Med. 2020;151:56-68. doi:1016/j.freeradbiomed.2020.01.179
18.  Ruiz D, Becerra M, Jagai JS, Ard K, Sargis RM. Disparities in environmental exposures to endocrine-disrupting chemicals and diabetes risk in vulnerable populations. Diabetes Care. 2018;41(1):193-205. doi:2337/dc16-2765
19.  Nardone A, Casey JA, Morello-Frosch R, Mujahid M, Balmes JR, Thakur N. Associations between historical residential redlining and current age-adjusted rates of emergency department visits due to asthma across eight cities in California: an ecological study. Lancet Planet Health. 2020;4(1):E24-E31. doi:1016/S2542-5196(19)30241-4
20.  US EPA Office of Air Quality Planning and Standards. Policy assessment for the review of the National Ambient Air Quality Standards for Particulate Matter. EPA-452/R-20-002. Environmental Protection Agency. Published January 1, 2020. Accessed November 22, 2022. https://www.epa.gov/system/files/documents/2021-10/final-policy-assessment-for-the-review-of-the-pm-naaqs-01-2020.pdf
21.  American Lung Association. Disparities in the impact of air pollution. November 17, 2022. Accessed November 22, 2022. https://www.lung.org/clean-air/outdoors/who-is-at-risk/disparities
22.  McKnight-Eily LR, Okoro CA, Strine TW, et al. Racial and ethnic disparities in the prevalence of stress and worry, mental health conditions, and increased substance use among adults during the COVID-19 pandemic – United States, April and May 2020. MMWR Morb Mortal Wkly Rep. 2021;70(5):162-166. doi:15585/mmwr.mm7005a3
23.  Liu Y-Z, Wang Y-X, Jiang C-L. Inflammation: the common pathway of stress-related diseases. Front Hum Neurosci. 2017;11:316. doi:3389/fnhum.2017.00316
24.  Schakel L, Veldhuijzen DS, Crompvoets PI, et al. Effectiveness of stress-reducing interventions on the response to challenges to the immune system: a meta-analytic review. Psychother Psychosom. 2019;88(5):274-286. doi:1159/000501645
25.  Grief SN, Miller JP. Infectious disease issues in underserved populations. Prim Care. 2017;44(1):67-85. doi:1016/j.pop.2016.09.011