Type 2 diabetes mellitus (T2DM) is a complex, multifactorial disease characterized by a progressive loss of adequate beta cell insulin secretion frequently tied to insulin resistance.1,2 The specific etiologies of T2DM are not completely understood, but there is a strong link between a number of risk factors and the development of T2DM.
According to the Annals of Internal Medicine clinical practice guidelines, the following factors increase the risk of developing T2DM:3
- Aged 45 years or older
- First-degree relative with type 2 diabetes
- Certain racial and ethnic groups including African, Hispanic, Asian, Pacific Islander, or Native American
- History of gestational diabetes
- Delivery of an infant weighing 9 pounds or more
- Polycystic ovary syndrome
- Being overweight, especially abdominal obesity
- Cardiovascular disease
- Hypertension
- Dyslipidemia, including low HDL cholesterol, high LDL cholesterol, and high triglycerides
- Other features of metabolic syndrome
The American Diabetes Association (ADA) lists the following additional recommended criteria for diabetes testing in asymptomatic adults:1
- Physical inactivity
- Other conditions associated with insulin resistance
- Prediabetes
- Certain medications including some HIV medications, glucocorticoids, thiazide diuretics, and atypical antipsychotics
- HIV
Race/Ethnicity Component
Certain racial and ethnic minority groups in developed countries, particularly those of lower socioeconomic status, experience higher rates of T2DM compared to the white individuals. According to Centers for Disease Control and Prevention (CDC) statistics, the estimated prevalence of T2DM between 2017-2020 among adult Americans (total estimate of 37.1 million) was significantly higher in Black (17.4%), Asian (16.7%), and Hispanic (15.5%) populations compared to white, non-Hispanic populations (13.6%).4
However, this trend does not hold in developing countries. In fact, according to the International Diabetes Federation, in 2021, the African region (not including north African countries considered to be a part of the Middle East) had the lowest prevalence of diabetes at 4.5% compared to 14.0% prevalence in North America and the Caribbean.5
The differences in T2DM prevalence among racial and ethnic groups in developed countries are not attributable to race and ethnicity in and of themselves; instead, they stem from social determinants of health, defined as the non-medical conditions of an individual’s life that affect overall health, functioning, and quality-of-life.6 Social determinants of health are broadly grouped into five areas: economic stability, access to and quality of education, access to and quality of health care, neighborhood and living environment, and social and community context.
Economic Stability
Annual income has been demonstrated to be significantly associated with risk of T2DM development. CDC statistics show that between 2018-2019, prevalence of diagnosed diabetes among adult Americans was highest in those with the lowest income.7 Among those earning below the federal poverty level (FPL), 14.1% had diagnosed diabetes compared to 10.8% prevalence among those earning 100-299% of the FPL and 5.6% among those earning ≥500% of the FPL.
An analysis of the 2005 Canadian Community Health Survey found that an estimated 1.3 million Canadians reported having T2DM, about 4.9% of the population. Prevalence of T2DM was highest in the lowest income group (<$15,000 annually) at 9.1% compared to only 2.2% in the highest income group (>$80,000 annually).8
According to the 2021 American Community Survey done by the United States Census Bureau (n=324,173,084), Black Americans make up the largest proportion of those living blow the FPL.9 Of respondents who identified as Black or African American, 21.8% were living below the FPL compared to 9.8% for white respondents. Similarly, 21.4% of American Indian or Alaskan Natives, 17.6% of Native Hawaiian or other Pacific Islanders, 17.5% of those of Hispanic or Latino origin, and 15.4% of those who identified as two or more races lived below the FPL.
Access to Health Care
A 2008 cross-sectional survey (n=1,731) asked participants what they perceived as barriers to getting needed medical care, with barriers including cost and coverage (e.g., insurance won’t cover visit, cost is too great), general access (e.g., no transportation, availability of childcare), and provider-related barriers (e.g., doctor doesn’t speak their language, doctors are untrustworthy).10 The survey found that cost and coverage were the leading barrier to care, with 73.4% of respondents reporting at least one concern related to cost and coverage. While general access was reported as a barrier by 62.6% of respondents, with that number higher among minority groups (white 59.3% compared to Black 67.9%, Hispanic 63.3%, and American Indian 77.1%). Provider-related barriers were the least reported at 29.3% overall, but again, that number was higher among minority groups (white 23%, Black 34.1%, Hispanic 48.1%, American Indian 43.2%).
Education
Level of education has been shown to be significantly associated with diabetes prevalence. According to CDC statistics from 2018-2019, adults with less than a high school education had the highest a prevalence of diagnosed diabetes at 13.4%.4 Among those with a high school education, prevalence was 9.2%, and among those with more than a high school education, prevalence was 7.1%.
An analysis of the 2005 Canadian Community Health Survey found that of the estimated 1.3 million Canadians with T2DM, there was higher prevalence among those with a lower level of education.8 Of those with only an elementary school education, prevalence was 6.6% compared to 4.3% among those with a high school education and 3.9% for those with a college education.
According to the 2021 American Community Survey done by the United States Census Bureau, minority populations have the lowest level of educational attainment.9 Of those who identified as white, 93.5% had a high school degree or higher and 38.3% had a college degree or higher compared to 88.0% and 24.9% respectively for Black Americans. Other minority groups also had significantly lower rates of educational attainment compared to white Americans, including American Indian or Alaskan Native (77.5% for high school and 16.1% for college), Native Hawaiian or other Pacific Islander (88.0% and 18.2%), Hispanic or Latino origin (72.4% and 19.7%), and two or more races (80.6% and 27.0%).
Environment
One’s living environment and neighborhood determine access to healthy eating options, an important contributor to diabetes risk. According to a 2009 report presented to the US Congress, non-white individuals in low-income areas are more likely to live >20 miles from a supermarket (3.5% vs <1%), posing a serious barrier to maintaining a healthy diet.11
An assessment of access to food stores across 28,050 zip codes found that 20% have access to a chain supermarket, 17% to a non-chain supermarket, and 72% to a grocery store.12 There were fewer food stores in low-income vs high-income areas, with an average of 0.16 chain supermarkets per low-income zip code compared to 0.48 per high-income zip code. Urban areas had better access, but again low-income areas had significantly poorer access with 0.45 chain supermarkets per zip code compared to 0.73 for high-income zip codes.
Additionally, racial and ethnic minorities are more likely to live in areas with poor water quality,13 air quality,14 and be more susceptible to weather and climate change.15
Long-term exposure to air pollution has been shown to be associated with T2DM. One cross-sectional analysis of 6,392 Swiss citizens over 10 years found that both particulate matter and nitrogen dioxide (NO2) exposure were associated with higher rates of T2DM development.16 The World Health Organization recommends that 10-year particulate matter exposure not exceed 20 μg/m3 and NO2 exposure not exceed 40 μg/m3. Those who developed T2DM had a significantly higher mean 10-year particulate matter exposure for both particulate matter (24.4 vs 22.2 μg/m3) and nitrogen dioxide (29.2 vs 26.7 μg/m3). For every 10 μg/m3 increase in exposure, the adjusted odds ratio (accounting for lifestyle characteristics, body mass index, and hypertension) for prevalent T2DM was 1.40 for particulate matter and 1.19 for NO2.
Although a direct link between diabetes risk and other environmental qualities, such as water quality and susceptibility to climate change, is unknown, poor environmental conditions contribute to worse overall health and increased stress.17
Social and Community Context
Race-related biases and discrimination in healthcare contribute to both poorer quality of care as well as mistrust of the health system among minority populations, which makes them less likely to receive medical care.10 A 2015 survey of white laypeople (n=92), medical students (n=194), and medical residents (n=28) found that misconceptions about biological differences between Black vs. white patients.18 These misconceptions included that Black patients have thicker skin (laypeople 58%, medical students 35%, residents 25%), Black patients age more slowly (laypeople 23% belief, medical students 20%, residents 14%), and Black patients have less sensitive nerve endings (laypeople 20%, medical students 7%, residents 4%).
Individuals facing all of the above outlined social disparities are also more likely to experience chronic stress, which has both psychological and physiological effects. The state of the evidence is mixed, with some studies reporting a link between increased stress and development of T2DM as well as poorer glycemic control while others reported no association. Further study is necessary to determine if there is a conclusive link.
However, there is a known link between stress and obesity, one of the more influential risk factors for development of T2DM. One study of 33 women found that participants who were chronically stressed were more likely to eat high fat, high sugar foods (1.42 vs 1.39 score on questionnaire of consumption habits) and have low levels of physical activity (69% vs 41% self-reporting low physical activity), leading to increased waist circumference (87.17 cm vs 84.17 cm) and abdominal adiposity (14.26 kg vs 13.95 kg).19
Risk Reduction
Both the Annals of Internal Medicine and ADA clinical practice guidelines recommend the following to prevent or delay the development of type 2 diabetes:3,20
- Adults with overweight or obesity should lose and maintain a loss of at least 7% of their initial body weight.
- At least 150 minutes per week of moderate-intensity physical activity, like brisk walking
- Eat a healthy diet with the goal of weight loss and reduction of total caloric intake.
These lifestyle modifications have been found to prevent or delay T2DM in even high-risk populations. The Diabetes Prevention Program Outcomes Study (DPPOS) found that maintenance of at least 7% weight loss and 150 minutes of physical activity each week significantly reduced T2DM incidence (Hazard Ratio [HR] 0.73, 95% Confidence Interval [CI] [0.65-0.83]).21,22 Over a mean follow-up of 15 years, there was a 7% difference in cumulative incidences of diabetes between the group receiving lifestyle intervention compared to placebo (55% vs 62%, Relative Risk [RR] reduction 27%). Although diet and exercise were the most effective ways to prevent diabetes, the DPPOS did find that medication such as metformin was also effective, with a cumulative incidence of 56% in the group receiving medication intervention, only 1% higher than the lifestyle intervention group and 6% lower than placebo (RR reduction 18%, HR 0.82, 95% CI [0.72-0.93]).
References:
- 2. Classification and Diagnosis of Diabetes: Standards of Medical Care in Diabetes-2022. Diabetes Care. Jan 1 2022;45(Suppl 1):S17-s38. doi:10.2337/dc22-S002
- Diagnosis and classification of diabetes mellitus. Diabetes Care. Jan 2014;37 Suppl 1:S81-90. doi:10.2337/dc14-S081
- Vijan S. Type 2 diabetes. Annals of internal medicine. Nov 5 2019;171(9):Itc65-itc80. doi:10.7326/aitc201911050
- National Diabetes Statistics Report. Centers for Disease Control and Prevention, U.S. Dept of Health and Human Services. Accessed June 22, 2023. https://www.cdc.gov/diabetes/data/statistics-report/index.html
- IDF Diabetes Atlas, 10th ed. International Diabetes Federation. Accessed June 15, 2023. https://www.diabetesatlas.org
- Healthy People 2030: Social Determinants of Health. U.S. Department of Health and Human Services, Office of Disease Prevention and Health Promotion. Accessed July 25, 2023. https://health.gov/healthypeople/objectives-and-data/social-determinants-health
- National Diabetes Statistics Report (Centers for Disease Control and Prevention, U.S. Dept of Health and Human Services) (2020).
- Dinca-Panaitescu S, Dinca-Panaitescu M, Bryant T, Daiski I, Pilkington B, Raphael D. Diabetes prevalence and income: Results of the Canadian Community Health Survey. Health Policy. Feb 2011;99(2):116-23. doi:10.1016/j.healthpol.2010.07.018
- American Community Survey: 2021 ACS 1-Year Estimates Subject Tables. United States Census Bureau. Accessed July 26, 2023. https://data.census.gov/
- Call KT, McAlpine DD, Garcia CM, et al. Barriers to care in an ethnically diverse publicly insured population: is health care reform enough? Med Care. Aug 2014;52(8):720-7. doi:10.1097/mlr.0000000000000172
- Ploeg MV, Breneman V, Farrigan T, et al. Access to affordable and nutritious food: Measuring and understanding food deserts and their consequences: Report to Congress. 2009.
- Powell LM, Slater S, Mirtcheva D, Bao Y, Chaloupka FJ. Food store availability and neighborhood characteristics in the United States. Prev Med. Mar 2007;44(3):189-95. doi:10.1016/j.ypmed.2006.08.008
- Schaider LA, Swetschinski L, Campbell C, Rudel RA. Environmental justice and drinking water quality: are there socioeconomic disparities in nitrate levels in U.S. drinking water? Environ Health. Jan 17 2019;18(1):3. doi:10.1186/s12940-018-0442-6
- Woo B, Kravitz-Wirtz N, Sass V, Crowder K, Teixeira S, Takeuchi DT. Residential Segregation and Racial/Ethnic Disparities in Ambient Air Pollution. Race Soc Probl. Mar 2019;11(1):60-67. doi:10.1007/s12552-018-9254-0
- Morello-Frosch R, Pastor M, Sadd J, Shonkoff SB. The climate gap: Inequalities in how climate change hurts Americans & how to close the gap. 2009. https://dornsife.usc.edu/assets/sites/242/docs/ClimateGapReport_full_report_web.pdf
- Eze IC, Schaffner E, Fischer E, et al. Long-term air pollution exposure and diabetes in a population-based Swiss cohort. Environ Int. Sep 2014;70:95-105. doi:10.1016/j.envint.2014.05.014
- The Impacts of Climate Change on Human Health in the United States: A Scientific Assessment. U.S. Global Change Research Program; 2016.
- Hoffman KM, Trawalter S, Axt JR, Oliver MN. Racial bias in pain assessment and treatment recommendations, and false beliefs about biological differences between blacks and whites. Proc Natl Acad Sci U S A. Apr 19 2016;113(16):4296-301. doi:10.1073/pnas.1516047113
- Aschbacher K, Kornfeld S, Picard M, et al. Chronic stress increases vulnerability to diet-related abdominal fat, oxidative stress, and metabolic risk. Psychoneuroendocrinology. Aug 2014;46:14-22. doi:10.1016/j.psyneuen.2014.04.003
- 3. Prevention or Delay of Type 2 Diabetes and Associated Comorbidities: Standards of Medical Care in Diabetes-2022. Diabetes Care. Jan 1 2022;45(Suppl 1):S39-s45. doi:10.2337/dc22-S003
- The Diabetes Prevention Program (DPP): description of lifestyle intervention. Diabetes Care. Dec 2002;25(12):2165-71. doi:10.2337/diacare.25.12.2165
- Long-term effects of lifestyle intervention or metformin on diabetes development and microvascular complications over 15-year follow-up: the Diabetes Prevention Program Outcomes Study. Lancet Diabetes Endocrinol. Nov 2015;3(11):866-75. doi:10.1016/s2213-8587(15)00291-0
