Hypertension, race, class & Puerto Rico!

Update: Author comments below.

PLoS ONE has an interesting paper out, Genetic Ancestry, Social Classification, and Racial Inequalities in Blood Pressure in Southeastern Puerto Rico. They're exploring the topic of African ancestry and hypertension, which seems to have a positive correlation, but where there is dispute as to whether that correlation is driven only by genes, or environment, or a combination. Puerto Rico is characterized by a wide range in admixture between Europeans & Africans (with a minor but significant amount of Amerindian). Additionally, because most variance in between population complexion is controlled by only a half a dozen genes there is going to be a lot of noise in the correlation between skin color and ancestry. In this small sample of 87 individuals, 37 white, 31 brown and 19 black, assayed on 78 ancestrally informative markers, the correlation was 0.63. Moderately strong, but one variable can only explain 40% of the variance on the other (some more juice would no doubt be squeezed by more markers, as well as using a continuous skin color metric based on reflectance).

Here's the plots of ancestry across the three classes:

i-0c7ea2356a905eac3773fee4e0bf7d0c-prblan.png

The means & standard deviations in African ancestry for the three classes were 0.19 & 0.10, 0.28 & 0.12 and 0.44 & 0.11. It is interesting that the black category in this community in Puerto Rico may very well be whiter than 90% of American blacks (10% of American blacks are 50% or more white).

The top line finding of this paper though is that once you control for the interaction of color with socioeconomic status the effect of African ancestry his sharply mitigated (to below statistical significance). There are some data from Brazil which also provide possible avenues of investigation into the interplay between perceived race coded through phenotype and the underlying ancestral quanta. Here is the regression table which lays out their model (I left one off because of how small the font is already):

i-c03f08008efef7c85cfe4ea0905657d0-regpue.png
i-bd828c27e794d59842f1a40eeebcb61b-pressure.png

And now here's a chart illustrating the interaction effect evident in the model above. What's going on here? This is showing you the interaction where higher SES among those coded as black seem to have higher blood pressure. They tiptoe around it in the discussion, but the implication is strong here that racism and negative life experience might have had some role to play in this. How this could play out concretely isn't too difficult to imagine. Years ago I read a book which was basically an ethnography of Brazilian culture, and in particular how blacks and whites related as a function of class. One of the illustrations of the travails of the lives of middle class blacks was a mother who told her children never to eat bananas in public, lest they be mocked by their white peers. The experience of racism by lower and middle class blacks was qualitatively different in this model. In particular, lower class blacks were often embedded in a predominantly black community and so could withdraw from interactions with whites, while middle class blacks were professionals who interacted with and lived with whites and so experienced stress and tension as a matter of course.

A possible novel finding in this paper was that taking into account the color X SES interaction they found a genetic association with hypertension. Association studies obviously have to account for population genetic substructure. Here they are suggesting that other environmental variables might be useful as well (in a world of infinite research dollars, of course!).

Nevertheless, I pointed out the fact that the blacks in this study aren't very black ancestrally to urge some caution (they do so as well). The sample size is small, and lots of variables are being manipulated and values coded (e.g., the racial classes are coarse). Who knows where the p-values might have fallen if the parameters were jiggled in another direction. The studies about people with African ancestry and hypertension include some nations where the overwhelming majority of the population is African ancestry (e.g. ,West Indies), but also there are data from African nations where hypertension isn't a problem. It seems likely that genes and environment are both a role in these sorts of "lifestyle" diseases, and that there are likely interaction effects at work.

Finally, instead of the racial angle, I wonder about the familial one. In these societies which are heterogeneous by origin siblings may be coded as different races. Dark-skinned siblings may be treated much worse than light-skinned siblings. It would be interesting to see the effect within families among siblings. These sorts of studies often get boiled down to "racism = bad health" in the American media, but I do suspect it's more complicated than that. Especially when other societies do not always have American conceptions of race.

Citation: Gravlee CC, Non AL, Mulligan CJ, 2009 Genetic Ancestry, Social Classification, and Racial Inequalities in Blood Pressure in Southeastern Puerto Rico. PLoS ONE 4(9): e6821. doi:10.1371/journal.pone.0006821

Addendum: I assume someone might quibble with my translation of the terms above as "white," "brown" and "black." So be it.

More like this

This is going to be fairly hard to prove that it is mostly biological because HP varies quite a bit within and between races.

This links to a study done back in 2005:

http://thestudyofracialism.org/viewtopic.php?t=5874&highlight=blood+pre…

It clearly shows...obviously African Americans and especially Caribbean blacks have lower levels of blood pressure than many Europeans. It is also pretty clear to anyone aware that blacks have a larger percent of their community concentrated in the lower income levels (in Latin America and the U.S.) and in the U.S. those blacks specifically have a "Southern" eating tradition which is much less "heart-healthy" on top of eating more junk food, etc. How does one sort through all that noise? My personal theory is it has to do with latitude and skin color. It may be environmental stress is less on blacks the closer they are to the equator (then add in societal stress of poverty, racism, etc).

Population
Total (%)
Men (%)
Women (%)

African-origin populations

-Nigeria
13.5
13.9
13.1

-Jamaica
28.6
23.4
31.8

-US black
44.0
43.1
44.8

European-origin populations

-US white
26.8
29.7
23.9

-Canada
27.4
31.0
23.8

-Italy
41.5
48.0
35.1

-Sweden
38.4
44.8
32.0

-England
41.7
46.9
36.5

-Spain
46.8
49.0
44.6

-Finland
48.6
55.7
41.6

-Germany
55.3
60.2
50.4

Thanks for highlighting our paper, Razib. A few points of clarification:

You mention the correlation between ancestry and skin color (r=.63) and suggest that the correlation might be higher using a reflectance-based measure. That is, in fact, what we did. Skin pigmentation isn't the focus of the PLoS ONE paper; see an earlier paper in Am J Public Health; which shows that blood pressure is associated with social classification but not with skin pigmentation, as measured by reflectance spectrophotometry. The purpose of mentioning the modest correlation between pigmentation and the genetic-based estimate of ancestry here is to reinforce the point that skin pigmentation is only a very rough proxy for genetic ancestry.

A related issue that may get lost here is that our approach to measuring "color" differs from standard approaches. Our measure is designed to estimate how people are perceived by others in terms of "color" during everyday social interaction. To get such an estimate, we used ethnographic data about how people categorize others by "color" in southeastern Puerto Rico (see Gravlee 2005; the emphasis on locally relevant color categories is an important reason to avoid translating them as you did). So, yes, the categories are coarse, but we think they approximate the way people are perceived in day-to-day interaction -- which, as you argue, shapes exposure to racism and other social stressors related to blood pressure.

Thanks again for the nod to our paper. I look forward to other comments, questions, and criticism.

Dr. Gravlee, great paper. I'm annoyed at how few scientists have attempted this kind of methodology.

Perhaps I missed this in the paper, but my question concerns the correlation between socio-racial classification and education reported in your paper.

Did you check to see if genetic admixture predicted any economic or educational outcomes over and above what was explained by socially classified race?

By Jason Malloy (not verified) on 11 Sep 2009 #permalink

Zeeb,

"Additionally, because most variance in between population complexion is controlled by only a half a dozen genes there is going to be a lot of noise in the correlation between skin color and ancestry. In this small sample of 87 individuals, 37 white, 31 brown and 19 black, assayed on 78 ancestrally informative markers, the correlation was 0.63."

Just to clarify (or reiterate Dr. Gravlee), "color" in this paper didn't refer to skin color, but to socio-racial classification from overall appearance -- which would probably involve many more genes of small effect related to facial variations (And probably to indicators of social class in the portraits, if racial classification in Puerto Rico is like some other non-US countries).

Racial admixture from skin color alone typically has a much weaker association with ancestry (average = .20), consistent with the small number of genes involved.

By Jason Malloy (not verified) on 11 Sep 2009 #permalink

Scratch that, the association is higher than I remembered. Identical to the overall appearance association in Puerto Rico even:
"In the samples that were measured with the DermaSpectrometer, we observed a significant positive correlation between melanin index and Indigenous American or West African ancestry, but the strength of the relationship was quite variable: Puerto Rico = 0.633; African Americans = 0.440; African Caribbeans = 0.375; Mexico = 0.212".

By Jason Malloy (not verified) on 11 Sep 2009 #permalink

"Years ago I read a book which was basically an ethnography of Brazilian culture, and in particular how blacks and whites related as a function of class. One of the illustrations of the travails of the lives of middle class blacks was a mother who told her children never to eat bananas in public, lest they be mocked by their white peers. The experience of racism by lower and middle class blacks was qualitatively different in this model. In particular, lower class blacks were often embedded in a predominantly black community and so could withdraw from interactions with whites, while middle class blacks were professionals who interacted with and lived with whites and so experienced stress and tension as a matter of course."

Thank you for stating this. I can tell you from first hand family experience that this type of thing also goes on in the United States. In fact, I have long argued that the black people in America who are so incensed by racism are not poor blacks, but middle class ones. In my experience (I am a black American) most poor blacks might believe there is racism, but often, outside of work their environment is completely black, so most of the time they do not speak about or probably think about racism. Middle Class blacks often associate with whites or in predominately white environments (especially upper middle class) most of the time, not just at work. They always have the experience of walking into a room that is predominately white, interacting with whites in the grocery store, restaurants, etc.

@Jason: We weren't focused on educational outcomes, and our data are limited to educational attainment (years or degree) and household income. But I just ran some quick-and-dirty analysis to look at how educational outcomes are associated with genetic ancestry and social classification. The short answer is that, once you include social classification, there is no association between genetic ancestry and years of education. Ditto for household income.

@Longman: I appreciate your comments about the unique stressors faced by middle class African Americans. There's a growing body of research that underscores your point. You may also be interested to know that my colleagues and I are doing new ethnographic research now on the types of stress blacks of varying socioeconomic backgrounds face in their day-to-day lives. We will use what we learn to develop better measures of stress exposure among African Americans, and within a couple of years, we should be able to say more about how the experiences you mentioned (e.g., being in predominantly white environments) relate to the risk of high blood pressure and other stress-related outcomes.

"The short answer is that, once you include social classification, there is no association between genetic ancestry and years of education. Ditto for household income."

Thanks! You realize that that has important implications for sociology. I would strongly recommend publishing it.

By Jason Malloy (not verified) on 15 Sep 2009 #permalink

LongMa

Interesting observation. What immediately came to my mind was Seasonal Affective Disorder where incidence of seasonal depression increases with increased latitude I have not seen racial breakdowns for this.
Since the causes are unknown and open to armchair theorizing.
I would imagine that other non-depressive symptoms might be found as well.
It is well know that in our Society, while myriads of findings of racial differences may be noted, any attempt to generalize such differences evoke the Thought Police.
We do know that identification with Tribe is quite important in Africa. But little studied is the . And psychological effects of separation from one's tribe. And whether this varies by race. Differences in anxiety level while in alien corn would produce differences in hypertension.

By plschwartz (not verified) on 15 Sep 2009 #permalink

Clarence C. Gravlee:

That would be a very interesting study that I look forward to reading. I think one area you might look into with middle class blacks (and up) is the work place, especially if they are white collar workers, specifically when blacks interview for jobs with white hiring managers. Also, when blacks are up for promotion. When blacks are concerned with appearing not to understand something so they keep quiet and may only mention it to another minority or some white person they trust. I have known blacks that are fairly paranoid in the office about how they are perceived, especially black men. For example, I know quite well that most African Americans feel that their negative behavior will be seen as more threatening or just far more negative than a comparable white person so they are often on guard. They feel they can not afford outbursts for example, even if a white man who is fairly popular in the office acts like this. As my friend once said, "we all know what we can get away with and what we can't compared to them". Blacks also worry about being discriminated against in terms of the assignments they are given or the career path they might feel they are being pushed into (often dead end grudge work). Some times it is just as simple as not being invited to lunch by white colleagues. I know one guy who has kept the fact his wife is white to himself for fear his predominately older white male management will respond negatively to him. I realize some of these things might sound paranoid or silly, but if one of these things happens to you once, you stay on guard and it is reinforced by the stories of other peers.

You might also look into blacks that have a significant number of white friends and when something is brought up, often race-related or even possibly about president Obama and his/her white peers have a different perspective what is their response. In my experience they often feel whites don't understand and keep it to themselves or maybe respond the opposite and get vary emotion. Most of the time the whites just defer for fear of appearing racist. I think this factor is a major reason why many blacks often do not associate with whites and specifically seek out other blacks to associate with even if they have to go out of their way, because they don't feel as stressed about interacting, the same might be true of whites as far as their association with blacks as well.