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While early studies of who was dying of Covid-19 identified risks such as obesity and having diabetes, there is a growing realization that those initial conclusions might have been misleading, obscuring a more significant explanation.

As researchers pull back their lens from individuals to population-level risk factors, they’re finding that, in the U.S., race may be as important as age in gauging a person’s likelihood of dying from the disease.

The higher the percentage of Black residents in a county, the higher its death rate from Covid-19 — even after accounting for income, health insurance coverage, rates of diabetes and obesity, and public transit use, finds a new study by researchers at the MIT Sloan School of Management. With those plausible explanations ruled out, “the causal mechanism has to be something else,” said applied economist Chris Knittel, the study’s senior author. “If I were a public official, I’d be looking at differences in the quality of insurance, conditions such as chronic stress, and systemic discrimination.”


The county-by-county analysis of Covid-19 death rates in the U.S. comes as more and more studies shift from the initial focus on individual-level factors that seem to increase people’s risk of dying to population-level ones, too, said experts in public health, demographics, and infectious disease.

One reason for the new focus is that “we’re not learning much more beyond what’s been observed from the start of the pandemic: that sex, age, and preexisting conditions put you at greater risk of dying” from Covid-19, said Aaron Glatt, an infectious disease physician at the Icahn School of Medicine at Mount Sinai. In almost every country, for instance, more men than women are dying of Covid-19, an imbalance that likely reflects both biology — women have stronger immune systems — and socialization: They seem to be following social distancing guidelines more than men, which could decrease the viral load they’re exposed to.


Also driving the shift in focus is that society-level influences are potentially more “actionable” than individual risk factors; you can’t change your blood type. A study posted to the preprint site medRxiv this month reported that type O is associated with lower risk of respiratory failure from Covid-19 and type A with a higher risk, but the paper hasn’t been peer-reviewed and it’s not clear how much difference blood type might make. “I wouldn’t tell one patient, thank God you have type O, but another, start preparing your will because you’re type A,” Glatt said.

To investigate population-level factors, MIT’s Knittel and graduate student Bora Ozaltun analyzed county-by-county mortality rates — the number of deaths from Covid-19 as a percentage of population, from April 4 to May 27. The mortality rate is more precise than the infection rate or the case fatality rate (the percent of diagnosed cases who die), which are imprecise because of inadequate testing. In contrast, although some Covid-19 deaths were incorrectly attributed to other causes, especially early in the U.S. outbreak, “deaths, sadly, are an absolute,” Knittel said.

They then used standard statistical tools to tease out which factors are most strongly correlated with mortality rates. Race stood out. Nationwide, the average county-level death rate from Covid-19 is 12 per 100,000 people. Counties with a Black population above 85% had a death rate up to 10 times higher. For every 10 percentage point increase in a county’s Black population, its Covid-19 death rate roughly doubles, Knittel said.

That meshes with other research. A study last month of 1,052 Covid-19 patients treated at Sutter Health hospitals in California, for instance, found that Black patients had 2.7 times the odds of hospitalization as non-Hispanic white patients, indicating more severe disease. And an analysis by scientists at the Harvard T.H. Chan School of Public Health found that the death rate in predominantly non-white areas is six times that in non-Hispanic white areas.

“Black people are dying of Covid-19 at a rate more than twice our share of the population,” said Malika Fair, an emergency medicine physician in Washington, D.C., and senior director of health equity programs at the Association of American Medical Colleges.

The MIT researchers’ key finding is that the underlying reasons for the link between race and death rate are not the usual suspects.

“Policymakers’ natural instinct is to think this correlation is because of income disparities, or having health insurance, or diabetes, obesity rates, smoking rates, or even use of public transit,” Knittel said. “It’s not. We controlled for all of those. The reason why [Black people] face higher death rates is not because they have higher rates of uninsured, poverty, diabetes, or these other factors.”

The Sutter study, too, adjusted for age, sex, comorbidities, and income; the higher hospitalization rate for Black patients wasn’t explained by any of those.

That leaves other factors. “If I were a policymaker,” Knittel said, “I’d be looking at things like the systemic racism that affects the quality of insurance African Americans have and the quality of the health care they receive.”

People with Medicaid or high-deductible plans, for instance, are less likely to have a primary care physician; 34% of Black people and 15% of white individuals are covered by Medicaid and therefore less likely than people with employer-sponsored insurance to have a regular physician.

“People who didn’t have a relationship with a primary care provider were much less likely to get tested,” said Georges Benjamin, a physician and executive director of the American Public Health Association. “Testing sites were put in affluent communities, or required a car, and testing kits were in short supply. Any time there is a shortage of something, minorities are less likely to get it.”

Without a primary care provider, Black people who thought they were infected were also likely to be turned away from hospitals, Benjamin said. “Someone without a primary care doctor doesn’t get into the ER as fast as someone whose doctor calls ahead,” he said. “At what point were your symptoms severe enough that you got into the health care system?” For people of color, it was likely later, he suggests.

“Black patients presenting with fever and cough were less likely to receive a referral for a Covid-19 test,” Fair said. That delayed appropriate care.

And once they do get into the system, research has found, the quality of care Black people receive for a variety of conditions, such as cardiovascular disease, is likely to be lower. Racism “is apparent in how we treat patients,” Fair said. “We still see differences in the care [for many conditions] given to Blacks and whites.”

Another possible factor in the high death rate among Black Americans is the well-documented health effects, including on the immune system, of chronic stress such as that caused by a lifetime of discrimination.

In the MIT study, the correlation between a county’s Covid-19 death rate and its proportion of Black residents was stronger within any given state than between states. “That tells me that there are important state-level differences that drive these deaths,” Knittel said. “African Americans are more likely to live in states with poor health care systems.”

Commuting via public transportation, relative to telecommuting, is also linked to a higher death rate. When public transit use is 20.6 percentage points higher in one county than another, its death rate is about tenfold higher.

Driving to work was also linked to a higher death rate. Many people working at their place of employment rather than home were in public-facing and therefore risky occupations such as health care, grocery stores, and public safety. “The correlation between death rate and driving to work suggests that just being at work, no matter how you get there, increases your risk of dying,” Knittel said.

Those positions are also filled disproportionately with people of color, likely contributing to the correlation between race and death rates. “Clearly, people who have jobs where they come into contact with others, from health care workers to bus drivers, are more likely to become infected,” the APHA’s Benjamin said. Although much about the pathology of the new coronavirus remains a mystery, the chance of becoming infected is partly a function of how much virus one is exposed to; the more infected people someone encounters, the higher that viral load can be.

The new population-level approach to understanding risk has prompted a rethinking of the role of conditions such as obesity and type 2 diabetes.

“Obesity is a marker of poverty and therefore of access to high-quality health care,” said Nina Schwalbe of the Mailman School of Public Health at Columbia University. Although the physiological consequences of obesity, notably high rates of inflammation, might contribute to Covid-19 severity, “obesity is a signal for so many of the social determinants of health, and we have to ask what this signal is telling us about vulnerabilities,” Schwalbe said.

That holds for type 2 diabetes as well. An analysis of 13 separate studies found that the disease is associated with 3.7 times the risk of having severe Covid-19 or dying from it compared to not having any underlying illness. This, too, is a disease of poverty, which means those who have it are more likely to live in crowded homes where “social distancing” is impossible, more likely not to have a primary care physician, and more likely to have jobs that increase their exposure to infected people.

The Sutter and MIT studies cast doubt on whether individual risk factors are as important as social determinants of health in affecting someone’s chances of contracting severe and even fatal Covid-19. “It should cause us to ask a different set of questions about what puts you at risk of hospitalization or death,” Schwalbe said.

More and more evidence is pointing to social determinants of risk, which puts the role of underlying health conditions in a new light. “Comorbidities are still used to blame people for how hard they are hit by Covid-19,” said Philip Alberti, senior director for health equity research at the AAMC. To reduce the U.S. death toll now that many states are seeing a new surge in cases, he said, “our response to this disease” must look beyond the strictly medical.

  • No mention is made of the effects of living in multi-generational families and of overcrowded living conditions. They must be factors as well.

  • Why do black people not have a primary care physician? Why did governments fail to have test sites in predominantly black populated areas? Why is obesity a marker of poverty while lots of whites are obese too (including the top dog in the White House)? Why is Type 2 diabetes a marker of poverty while it is rampant in also affluent elder people of all colors? Where is the official R&D on the potential that the variations in genetics may result in different reactions to the new virus? The generalizations in this article are just parrotting of the popular squealing – simple opportunism to write just another piece without solid research. Journalism stinks.

  • It would also be interesting to crunch the number of deaths to actual skin color. Not White, Black, Brown. But a numeric scale where you have 100 values of skin color to correlate to deaths or days in hospital till recovery. I bet you will see that Vitamin D levels will be closely tied to that numeric value.

    Also no mention of Vitamin D, Vitamin C or Zinc in this aricle. Wow that news has been going around for years and still Doctors have their heads in the sand.

    • You are correct. There is so much anecdotal data on Vitamin D and Covid 19 that there have been 20+ Clinical Trials registered to find out what is exactly going on. It does not take a rocket scientist to look up why Vitamin d is important as a hormone that signals the Innate and Adaptive immune system. Unfortunately there has to be the right amount in the system to allow the body to keep homeostatic balance while the body fights infection.

  • In the research article ‘Differences in Weight Perception Among Blacks and Whites’ ( the authors state, as part of their conclusion, “Although blacks had higher prevalence of obesity compared with whites, researchers found that blacks had a smaller discrepancy between perceived and ideal body size, suggesting that blacks were more comfortable with their weight. Black participants tended to select larger ideal figures than white participants. In addition, cultural values in the black community place more weight on self acceptance and character over physical appearance.” I believe the majority of the population realizes that being overweight is hard on our bodies (high blood pressure, diabetes, heart disease, certain cancers) but if our family and friends assure us that it’s not really a concern- we love you just the way you are- it may be difficult to get the support needed to deal with the tough issue of losing weight, to benefit our health. The question becomes ‘how do we go about changing our cultural norms so that our culture benefits health wise?’.

  • It would be interesting to compare the clinical outcomes for hospitalized Black Covid-19 patients treated by white physicians (some who may be overtly racist, and the rest all subject to implicit bias) versus those treated by Black physicians.

    If the cohort of Black COVID-19 patients treated by whites had worse outcomes there are two (there are always only two solutions in today’s zeitgeist of absolutism) solutions for this disparate impact;

    1. Mandate white physicians undergo re-education to overcome their white privilege, innate prejudice, and implicit bias. Annual retraining would be required for the renewal of licensure.

    2. Only allow white physicians to treat Black patients under the supervision of Black physicians, PAs, Nurse practitioners, of RNs. The Black supervisor would have veto power over the white physician’s treatment plan.

    • Extremely important “IF” you seem to be on the verge of assuming. Let’s start with an examination of Vitamin D absorption and it’s converse relationship with folate before we start painting with such broad strokes on our medical community. Keeping this evidenced based will not only reduce tension and conflict…it will save lives. If melanin levels are a true cause (actual evidence exists here), let’s research that before changing policy based on conjecture that could cause time delays and kill people.

    • And if there’s no difference? What if you find out that white patients treated by black physicians have worse outcomes than black patients treated by either black or white physicians?

      Would you announce these results at risk of being branded a racist?

  • No – focus on causes unless there is a clear cause-effect relationship between race and the fatality rate.

    We are not making minority communities engage in unhealthy lifestyles – it is each individual member of those communities who are making that choice for themselves.

    Claiming ‘racism’ does nothing but enable those unhealthy lifestyle choices because now they have no responsibility for the choices they made.

  • It would be interesting to know what inserting Vitamin D deficiency as a variable would show.

    • Exactly. To not mention this proven correlation (and likely causal factor) at all in the article borders on reckless journalism worthy of our current fast food media conglomerates. Check Rhonda Patrick’s work on the subject as a basic primer. Best case this is poorly researched. Worst case it is purposefully irresponsible to get clicks…our country’s divisiveness levels and wounds be darned. Just wow Sharon Begley.

  • On the one hand this article says not having a car puts the person at risk(harder to get to testing site). And then the article goes on to say those who drive to work get sicker. Which is it?

    • I understood it to be saying that those who have to drive to work, as opposed to being able to work from home, are at higher risk.

  • one factor that is not mentioned in this article for various reasons is lack of proper education or what I term educational inequality ; the public school system in the US is at best below average compared to the world : look up the PISA testing system for dismal US results; a virus does not discriminate however one must understand contact surfaces, parts per million, survivability on surfaces and human cleaning procedures daily; observe a self check aisle at a grocery store and see how many wear masks but touch that scanner thousands of times a day without being cleaned at all

    • Unfortunately, there are a heck of a lot of ignorant, (especially of science, but really everything) people in the US who do not have a clue what to do to protect themselves.
      To some extent, they act like people did before science knew about a lot of things – they try to explain things away without any solid basis for their beliefs and then get fatalistic about doing anything to protect themselves.

  • “Obesity is a marker of poverty and therefore of access to high-quality health care,” Obesity may be a marker of poverty but in most cases it is due to people overeating/eating the wrong kinds of food/lack of exercise. These are all individual choices. Walking 40 minutes 3-4 times a week and not eating fast food or flavored drinks will in most cases pay off. What are you trying to say that poor people are too stupid to take care of themselves? That rich people are force feeding poor people and restraining them on the couch for hours at a time. Don’t you think that people (even poor people) can take some personal responsibility?

    • Both the data driven scientists, and Carlos have valid points. That particular point of obesity is simply a marker, validating a more complicated social construct built squarely on the results of systemic racism. How can we not see that?

    • Carlos, as you say obesity may be due to some individual choices, but if you are living in poverty chances are you don’t have a safe area where you can walk for 40 minutes.

      You may also be holding down a couple of jobs – which is all to common these days. Try fitting in that type of exercise into your schedule especially if children are involved.

      Buying the food that is better for you: Some neighborhoods don’t have grocery stores for miles and don’t forget the cost.

      Some times obesity is more complicated than individual choices.

    • Ron: When you have to resort to ‘complicated social constructs’ you are making excuses for them.

      And doing this will not solve anything. Because if you tell them it’s somebody else’s fault then you have absolved them of responsibility for lifestyle choices they made.

      If we stopped making excuses for them and started holding them responsible for poor life decisions – then things will start to get better.

      A principle of leadership is that people will live up to – or down to – the standards you hold them to. Holding the black community to lower standards is not only perpetuating the problem – it’s also pretty racist. If you hold them to lower standards you are in effect saying that they are not as good as the groups you are holding to higher standards.

    • Angela: Your response was nothing but speculations and excuses. If somebody is an alcoholic – are you doing them any favors by making excuses for them?

      And would you make these same excuses if the issue were obesity among whites?

    • Angela is absolutely correct that obesity is a sign of poor economic status. Look it up. It is among all colors of skin. Very often these people live in “food deserts” where access to fresh food is a huge challenge-and most food is bought at the corner gas station or store. Compare the cost of milk to soda, chips to meat etc. Limited budgets aim to FILL bellies, not necessarily able to also make healthy choices as their is NOT a cheap healthy choice. And this population may not have access to adequate cooking facilities, nor have the time or knowledge to know how to cook healthy. It is obvious you have never actually worked with this population.

    • Monyka – I am not trying to take sides in a political discussion, but geez, one does not need to have money to not be fat – there are poor thin people all over the world – now, it is very easy, I think, to get fat in the US, and it could be easier if you are poor – but good grief, laying off carbs is at least half of it.
      However, I will say, it is often the fault of the family, if parents do not keep the kids away from junk food and keep them active, they grow up a little overweight and then just keep ballooning – everyone sees that, let’s be honest, all the time, in every color of people- keep your kids thin people – that is the answer maybe half our national health problems in the long run. KEEP THE KIDS THIN.

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