“[A] very attractive case can be constructed, all based upon a genetic defect in sodium excretion that is more prevalent among blacks. Perhaps blacks, who originally lived in hot, arid climates wherein sodium conservation was important for survival, have evolved the physiologic machinery which protects them in their original habitat but makes it difficult for them to handle the excessive sodium they ingest when they migrate.” Kaplan & Lieberman, Clinical Hypertension. 4th ed, 1986
In this continuing series highlighting health and fitness issues inextricably linked to Systemic Racism, I am highlighting a wide spread and largely debunked hypothesis linking slavery survival and hypertension among Black Americans (BA). While I used many sources of information for this article, much of the article is inspired by the 2018 editorial by DiCarlo and Lujan, The “African gene” theory: it is time to stop teaching and promoting the slavery hypertension hypothesis, Dr. DiCarlo’s thoughtful comments. This topic is important for a few reasons.
- Race is a social construct without biological relevance, and actually reflects external human diversity.
- Hypertension is far more prevalent in Black men and women (~50%) than White men and women (~30%).
- Promoting the hypothesis as fact undermines the potential care black persons receive, and the search for other possible links.
- It perpetuates the false narrative of blaming a group’s disease on the actions of that group. This includes blaming black co-morbidities on their poor diet or lifestyle, while ignoring the health and socio-economic drivers of health and healthcare, which we know are linked to Systemic Racism.
Black Health Disparities are Real
It is widely accepted that racial disparities between whites and minorities exist on numerous levels, even after accounting for socio-economic factors. This is hugely problematic among black communities because when socio-economics are added back into the equation, those health problems are compounded. For example, 80% of BA women are overweight or obese compared to 64.8 percent of non-Hispanic white women, with the leading causes of death being cardiovascular disease and cancer.AHA Stats 2015 In 2017, 12.6 percent of BA children had asthma compared with 7.7 percent of non-Hispanic white children, and is strongly linked to living in more polluted areas. And as indicated above, 42% percent of BA adults over age 20 suffer from hypertension. While race is clearly associated with these disparities, the underlying causes are not so simple to tease out.
Slavery, a red herring hypothesis?
The Slavery Hypothesis, proposed in 1983, offered a convenient explanation to a complex perpetual problem. On the surface, linking slavery to poorer black health seems a reasonable hypothesis tying together Darwinism and genetics into a neat package. Commonsense would support the notion that slave ships were ultimate tests of survival and adds an almost courageous aspect to slavery, but is it correct? Could an enhanced hypertensive response to salt be linked to slave survival during sea voyages? To answer this, we need to examine the evolution of the hypothesis itself.
The initial hypothesis hinged on enslavement of Africans from areas with low salt availability. While salt use varied across Africa, most slaves originated from the West Coast of Africa, which was not necessarily lacking salt. One line of argument for the hypothesis comes from evidence showing that humans living at equatorial latitudes have genetic variations that support salt retention, and that salt retention explains nearly 80% of the differences in cardiovascular and nearly 50% of overall life expectancy in blacks. These types of “feast or famine” connections are common in health and are also used to explain away obesity across the board. Unfortunately, they often ignore counter-evidence, outliers, and the complexity of chronic disease. ‘
Now, as the narrative goes, slaves who could selectively retain salt, could better endure heat stress and dehydration. Thus, one relatively short sea voyage dramatically sped up “natural selection” by filling the Black American gene pool with a salt retention advantage, which served them well for hundreds of years toiling on plantations under more heat stress and poor diet quality. Once freed, this selection turned to disadvantage, as they adopted a higher quality diet. But again, this simplistic views fails to account for the wide variations in dietary patterns among BA beginning in the early 20th Century. Moreover, there are many other racial/ethnic groups also sharing that genetic feature that do not exhibit high BP.
Genetics is more than just genes
No other suspect receives more blame for ill health than our genes. And while genetics are basis of everything we are, the influence of environmental factors have at least as much, if not more impact because they produce a double whammy. First, environment results in a direct effect, where we must respond to a stressor and adjust or acclimate. However, there can be another, more lasting effect, in some cases multi-generational effect. This effect is not changing our DNA, rather, it’s resulting in some genes turning on, or off, or perhaps both; this is epigenetics.
Black hypertension: Nature and Nurture
Looking at all the evidence, I’ll offer my opinion on this issue. It appears that slavery likely plays a role in the prevalence of hypertension among BA, just not the genetic selection one might like to connect. Epigenetics helps us explain how, without alter DNA, we can see profound, multi-generational changes in select populations due to environmental pressures. The reality is that slavery tore millions of Africans from their homes, transported them to numerous regions from South to North America where they endured centuries of poor nutrition, extreme hardships, and even after freedom, poverty, terrorism, and massive stress. The link between stress and epigenetics is well established and would explain the root mechanisms for the overall prevalence of cardiovascular diseases we see among BA. When we add in the continued exposure to environmental factors driven by systemic racism (e.g., low income, pollution, police brutality) we should not be surprised by these numbers. However, all of this belies the real problem of blaming slavery on poorer Black health.
A new wrinkle in genetics
With all the focus on genetic bottlenecks, I thought it was very convenient that a recent publication by Michelleti and colleagues counters the argument of “black genes” being the root of “black diseases”. To start, we need to remember that race is a social construct with no biological basis; the actual genetic differences between any racial group is exceedingly small. The differences in salt retention are not actually a feature of race, but one of latitude, where those in hot climates are more heat adapted. Even if, however, slaves survival “selected” for salt retention, the slave trade, including wide spread rape by white owners would have helped diversify that narrow gene pool. In this instance, the genes do not lie. As Michelleti et al. conclude:
Patterns of variation across the Americas, such as lower African ancestry and a higher African female sex bias can be attributed to socioeconomic factors, non-African male admixture, and inhumane treatment of enslaved people.
So white slave owners contributed a significant amount of genetic diversity to American blacks, and socioeconomic factors, and the atrocities of slavery determined the genetic make-up of BA. Another very interesting finding was that BA are largely of Nigerian ancestry due to slave trading patterns. Why does this matter? It turns out that the prevalence of hypertension in Nigeria are slightly less than those of White Americans further undermining the slave hypothesis.
We have all heard the “bad genes” argument. Endlessly blaming your obesity or alcoholism on your genes will not cure either one anymore than trying to blame a largely discredited slavery hypothesis on BA health. Why? Because whatever the root cause was the real reason for the ills of Black America is systemic structural economic, and social racism. We cannot fix this problem ever without fixing the problem that drives all of this. That’s not political opinion, its uncomfortable fact. I’ll close with a quote from a 2007 article by Osagie K. Obasogie:
What’s so pernicious about this “bad gene” theory is that it attributes current health disparities to actions taken nearly four centuries ago, when the more relevant issue may very well be what is happening today. Reducing health disparities to genes obscures more sensible conversations about the contemporary nature of discrimination, how it affects minority health and how best to improve health outcomes.
Have a comment or correction? Drop me an email!
DiCarlo and Lujan. Adv Physiol Educ 42: 412–416, 2018
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Cutler et al. Racial Differences in Life Expectancy: The Impact of Salt, Slavery, and Selection. 2005.
Dirks and Duran. African American Dietary Patterns at the Beginning of the 20th Century. J. Nutr. 131: 1881–1889, 2001.
Cowell. Epigenetics – It’s not just genes that make us. British Society of Cell Biology.
Garrie. Epigenetics: Can stress really change your genes? The Conversation. March 14, 2016.
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Adeloye. An estimate of the prevalence of hypertension in Nigeria: a systematic review and meta-analysis. J Hypertension. 32 (1): 1-13, 2014.
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