Why Are Some Diseases More Common in Black People?

The higher rates of conditions like sickle cell disease, hypertension, lupus, and certain cancers among Black Americans stem from an interlocking set of causes, not a single explanation. Some involve genetic variants shaped by ancient survival pressures. Others trace to the cumulative biological toll of racism and social disadvantage. Still others reflect how neighborhoods, medical devices, and clinical practices systematically work differently for Black patients. Treating any one of these categories as “the reason” misses the picture, and that incomplete picture has real consequences for how diseases get prevented and treated.

Genetic Variants That Evolved as Protection

A handful of genetic variants are genuinely more common in people of African descent, and in most cases, the reason they persisted is that they once offered a survival advantage. The best-known example is the sickle cell trait. The mutation behind sickle cell disease is estimated to have originated more than 7,000 years ago, and despite causing severe illness when a person inherits two copies, it persisted because carrying just one copy provides substantial protection against severe malaria caused by Plasmodium falciparum.¹ In regions where malaria was historically deadly, that tradeoff kept the mutation circulating at high frequencies.

A similar story applies to the APOL1 gene. Certain APOL1 variants give the immune system extra ability to kill trypanosomes, the parasites that cause African sleeping sickness. One variant, called G2, is associated with roughly a five-fold reduction in susceptibility to the acute form of sleeping sickness in people carrying even a single copy.² Research in Malawi confirmed this protective effect, finding that carriers of the G2 allele were strongly protected against infection.³ The catch is that those same APOL1 variants are strongly associated with kidney disease in African Americans today.⁴ The parasite is gone from North America, but the kidney risk remains.

Another example involves the Duffy antigen receptor. Roughly 70% of African Americans lack expression of the Duffy antigen on their red blood cells, a trait that originated as protection against a different form of malaria. Researchers have raised the possibility that the absence of this receptor, which normally binds certain signaling molecules involved in blood vessel growth, could influence susceptibility to prostate cancer, though the link remains under investigation.⁵

These examples share a pattern: a gene variant that was beneficial in one environment can become harmful in another. They account for a real slice of disease disparity, but only a slice. Sickle cell disease is genuinely genetic. Hypertension in Black Americans is not explained by any single gene variant in the same way.

When the Body Keeps Score of Discrimination

One of the more striking findings in health-disparities research is that the chronic stress of living with racism appears to physically age the body faster. Researchers call this “weathering,” and the evidence for it has grown steadily. A systematic review of studies examining the concept found support across multiple biological markers: Black Americans showed higher allostatic load (a composite measure of wear and tear on the body’s stress-response systems), shorter telomeres (the protective caps on chromosomes that shorten with age), greater inflammation, and epigenetic changes consistent with accelerated aging.⁶

How big is the gap? One study found that in each age group, Black Americans’ allostatic load scores were roughly comparable to those of White Americans who were ten years older, suggesting that the biological aging process runs ahead of calendar age.⁷ More recent work using data from the Health and Retirement Study found that socioeconomic factors and social vulnerabilities, rather than health behaviors or medical conditions, were the dominant contributors to this accelerated biological aging gap between Black and White adults.⁸

Research has started to identify specific pathways through which discrimination gets “under the skin.” In a study of Black women, experiences of racial discrimination were associated with accelerated epigenetic aging across multiple methylation clocks, and higher racism scores correlated with measurable changes in DNA methylation at specific chromosomal sites.⁹ A separate study found that racial discrimination was associated with altered brain connectivity patterns in Black women, and these neural changes were in turn linked to DNA methylation age acceleration, suggesting a brain-to-biology pathway for how discrimination translates into premature aging.¹⁰

There is a silver lining in the research, though. Among African American mothers, social-support seeking appeared to buffer the aging effects of discrimination. At the highest levels of social support, the link between racial discrimination and accelerated biological aging disappeared.¹¹ This suggests the pathways are modifiable, not inevitable.

The Neighborhoods People Were Sorted Into

Where you live affects what you breathe, what you eat, and what diseases you develop. For Black Americans, residential geography was shaped for decades by redlining, a federal policy that graded neighborhoods by perceived lending risk, with the worst grades systematically assigned to Black communities. Those grades did not simply disappear when the policies ended. A study of contemporary environmental and health data found that neighborhoods given the worst redlining grades still have the highest levels of carbon monoxide, fine particulate matter, sulfur dioxide, and volatile organic compounds. Black residents in those neighborhoods faced about 2.3 times the risk of uncontrolled or severe asthma compared with residents in the best-graded neighborhoods.¹²

Food access follows a similar pattern. African Americans are more likely to be diagnosed with diabetes and more likely to live in areas with limited access to affordable, nutritious food. Food insecurity is recognized as an important modifiable risk factor for worsening outcomes in chronic diseases like type 2 diabetes.¹³ When the grocery stores in your neighborhood carry fewer fresh vegetables and more processed food, managing blood sugar becomes harder regardless of your willpower or genetics.

Diseases Where Biology and Disparity Collide

Some conditions illustrate how genetic factors and social determinants can be difficult to untangle. Triple-negative breast cancer, an aggressive subtype, is about two to three times as common among African American women as among White American women. One study found that 28% of breast cancers in African American women were triple-negative, compared with 12% in White women.¹⁴ The same study found that once you compared the tumors at the molecular level, they were more similar than different, with only a single pseudogene distinguishing them. Yet the elevated incidence is also seen in women in western sub-Saharan Africa, suggesting that specific genetic components of geographically defined African ancestry play a role in susceptibility, not just disparities in screening or care.¹⁵ In other words, both biology and disparities contribute, and researchers are still arguing about the relative weight of each.¹⁶

Systemic lupus erythematosus is about three times more common in African American women than in women of other races, and tends to progress faster and cause more severe organ damage.¹⁷ Genetic research has identified B cell-related gene variants in women of African ancestry that may contribute to susceptibility.¹⁸ But racial discrimination itself is associated with disease activity and organ damage in Black women with lupus, suggesting that the stress pathways described earlier actively worsen the course of the disease, not just the likelihood of getting it.¹⁹

Uterine fibroids show a similar blend. Black women develop fibroids at higher rates, at younger ages, and with greater severity. Research comparing the gene expression and DNA methylation profiles of uterine tissue from Black and White women has found differences suggesting that the uterine tissue of Black women may be more susceptible to developing fibroids, pointing toward a biological component.²⁰ At the same time, delays in diagnosis and treatment, shaped by the same access and bias barriers that affect other conditions, compound the problem.

How Medical Tools and Standards Can Distort the Picture

Some of the disparity is not about who gets sick but about how illness gets measured and detected. Pulse oximeters, the fingertip clips that estimate blood oxygen levels, are less accurate in people with darker skin. The devices tend to overestimate oxygen saturation in darker-skinned patients, particularly when oxygen levels are genuinely low.²¹ A systematic review confirmed this bias is consistent across studies: pulse oximeters systematically overestimate oxygen in individuals with darker skin tones, which can delay recognition of dangerously low oxygen levels and the interventions that follow.²² During the COVID-19 pandemic, when oxygen monitoring was critical for deciding when to hospitalize patients, this device bias had life-or-death implications.

Clinical formulas have carried their own biases. For years, the standard formula for estimating kidney function included a race-based multiplier that assigned higher kidney function scores to Black patients simply because they were Black. The effect was to systematically overestimate how well a Black patient’s kidneys were working, which could delay referrals to specialists, delay placement on transplant waiting lists, and delay the start of dialysis.²³ Major medical organizations have since moved to remove this race adjustment, but its consequences accumulated over decades of use.

Bias in Who Gets Treated and How

Even when a Black patient is correctly diagnosed, treatment can differ. An analysis of chronic pain management found that Black patients had significantly lower odds of receiving interventional pain referrals, neurosurgical referrals, and opioid therapy compared to White patients, even after adjusting for sex, pain type, and other treatments being received.²⁴ These are not small differences in subjective comfort; untreated or undertreated chronic pain drives people toward disability, depression, and worsened outcomes for other conditions.

Part of the problem is surprisingly basic: false beliefs about biological differences. A study of White medical students and residents found that half endorsed at least one false belief about Black bodies, such as that Black people’s skin is thicker or their nerve endings are less sensitive. Students who held these beliefs rated Black patients’ pain as lower and made less accurate treatment recommendations.²⁵ These are not beliefs from a century ago; they were documented among people in medical training in 2016.

The legacy of historical medical abuse also affects engagement with the healthcare system. Research on colorectal cancer screening among African Americans has identified medical mistrust as a persistent barrier, with participants explicitly citing awareness of the Tuskegee syphilis study, in which Black men were deliberately left untreated, as a reason for their wariness.²⁶ When people avoid or delay preventive care because they do not trust the system, diseases get caught later and outcomes get worse, inflating the apparent disease burden in that population.

Maternal and Reproductive Health

The disparities are especially stark when it comes to pregnancy. Black women in the United States experience disproportionately adverse pregnancy outcomes, including maternal mortality, compared to women of other racial and ethnic groups. Structural racism and bias in medicine are recognized as compounding the problem, and the disproportionate impact of COVID-19 on communities of color may have widened the gap further.²⁷

Researchers are working to understand the physiological pathways involved. Black women show differences in uteroplacental blood flow, oxidative stress, and inflammatory markers compared to White women during pregnancy. These differences may reflect the accumulated effect of different social and environmental exposures rather than innate biological tendencies, and they are linked to the leading causes of maternal and infant death.²⁸ The point is worth pausing on: when your body has been under greater stress for longer, pregnancy starts from a different physiological baseline.

The Genomics Gap

African populations have the highest genetic diversity of any continental group on Earth, which makes them the most important population for understanding human disease genetics. Yet they are the most underrepresented in the research that drives modern medicine. As of 2021, only about 1% of genome data used in large-scale genetic association studies came from African populations, a figure that actually decreased from about 3% just two years earlier.²⁹ This underrepresentation affects cancer research especially: African genetic diversity influences cancer susceptibility, tumor biology, and how people respond to treatment, but those insights are largely missing from the datasets that precision medicine relies on.³⁰

The practical consequence is that risk calculators, drug-dosing guidelines, and genetic tests developed overwhelmingly on European-descent populations may perform poorly for Black patients. A genetic variant flagged as benign in a study of White Europeans might carry different significance in someone with West African ancestry, or vice versa. Until the research base catches up, precision medicine is less precise for the people who, paradoxically, carry the most genetic information.

Why “Race” Is a Blunt Instrument for Understanding Disease

An important caveat runs through all of this: race is a social category, not a clean biological one. Two people classified as “Black” in the United States can be more genetically different from each other than either is from a “White” person. Using race as a stand-in for genetic ancestry bundles together people with very different genetic backgrounds and very different exposures to racism, poverty, and environmental hazards. Researchers have argued that this conflation actively harms Black patients, because it can lead clinicians to attribute health differences to innate biology when the real drivers are structural.³¹

The more productive approach, as genomics and epidemiology have matured, is to study the specific genetic variants that matter (like APOL1 or sickle cell mutations) alongside rigorous measures of structural racism, neighborhood environment, and healthcare access. Blaming “Black genetics” for higher disease rates misses the fact that most of the disparity evaporates when you account for poverty, discrimination, environmental exposure, and unequal medical treatment. And the genetic factors that do exist almost always trace back to ancient survival tradeoffs, not to any inherent vulnerability.

Skin Pigmentation and Vitamin D

One biological factor that occasionally gets folded into disparity discussions involves skin pigmentation and vitamin D. Human skin color evolved as an adaptation to ultraviolet radiation: darker skin protects against UV damage and folate degradation in high-sunlight environments, while lighter skin allows more vitamin D synthesis in low-sunlight environments.³² This is a straightforward evolutionary adaptation driven by a polygenic genetic architecture that varies across global populations.³³ Black Americans living in northern latitudes tend to have lower vitamin D levels on average, and low vitamin D has been linked to a range of health conditions from bone disease to cardiovascular risk. However, vitamin D levels alone do not explain the disease-rate differences discussed throughout this article. The connection is real but it is one thread in a much larger tapestry, and supplementation trials have not reliably closed health gaps on their own.