October 17, 2008

Epigenetic effects of slavery in African Americans (?)

I can't say I buy the thesis of these two papers, namely that inherited epigenetic effects from the days of slavery are responsible for birth-weight and cardiovascular disease (CVD) disparities between whites and blacks in the US.

Does anyone know of any studies of birth weight or CVD in biracial children with a white vs. a black mother, with otherwise similar admixture proportions? An expectation of this theory is that the former should have a higher birth weight.

American Journal of Human Biology doi: 10.1002/ajhb.20824

Low birth weight of contemporary African Americans: An intergenerational effect of slavery?

Grazyna Jasienska

Abstract

The average birth weight in the contemporary African-American population is about 250 g lower than the average birth weight of European Americans. Differences in genetic and socioeconomic factors present between these two groups can explain only part of birth weight variation. I propose a hypothesis that the low birth weight of contemporary African Americans not only results from the difference in present exposure to lifestyle factors known to affect fetal development but also from conditions experienced during the period of slavery. Slaves had poor nutritional status during all stages of life because of the inadequate dietary intake accompanied by high energetic costs of physical work and infectious diseases. The concept of fetal programming suggests that physiology and metabolism including growth and fat accumulation of the developing fetus, and, thus its birth weight, depend on intergenerational signal of environmental quality passed through generations of matrilinear ancestors. I suggest that several generations that have passed since the abolition of slavery in the United States (1865) has not been enough to obliterate the impact of slavery on the current biological and health condition of the African-American population.

Link

American Journal of Human Biology doi: 10.1002/ajhb.20822

Epigenetics and the embodiment of race: Developmental origins of US racial disparities in cardiovascular health

Christopher W. Kuzawa, Elizabeth Sweet

Abstract

The relative contribution of genetic and environmental influences to the US black-white disparity in cardiovascular disease (CVD) is hotly debated within the public health, anthropology, and medical communities. In this article, we review evidence for developmental and epigenetic pathways linking early life environments with CVD, and critically evaluate their possible role in the origins of these racial health disparities. African Americans not only suffer from a disproportionate burden of CVD relative to whites, but also have higher rates of the perinatal health disparities now known to be the antecedents of these conditions. There is extensive evidence for a social origin to prematurity and low birth weight in African Americans, reflecting pathways such as the effects of discrimination on maternal stress physiology. In light of the inverse relationship between birth weight and adult CVD, there is now a strong rationale to consider developmental and epigenetic mechanisms as links between early life environmental factors like maternal stress during pregnancy and adult race-based health disparities in diseases like hypertension, diabetes, stroke, and coronary heart disease. The model outlined here builds upon social constructivist perspectives to highlight an important set of mechanisms by which social influences can become embodied, having durable and even transgenerational influences on the most pressing US health disparities. We conclude that environmentally responsive phenotypic plasticity, in combination with the better-studied acute and chronic effects of social-environmental exposures, provides a more parsimonious explanation than genetics for the persistence of CVD disparities between members of socially imposed racial categories.

Link

19 comments:

  1. Papers like this make me shake my head in wonder.

    There are a number of factors which could explain the difference in birth weight without having to resort to hand waving and some kind of epigentic echo down through the generations.

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  2. Nothing reparations can't fix. Geez, what next......

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  3. I initially thought of a few things.

    1) What are the West African (Nigerian, Ghanian, etc ) norms? Were any Africans tested who were born in the US from Nigeria, Ghanians who have no white admixture?

    I bring this up, because could this be the result of some incompatibility in genes due to the 20% white admixture in the average African American?

    2) Calcium/vitamin D levels?

    What are they and is there a cline in latitude in the United States where African Americans in the South of the same general complexion have larger babies?

    I read a report awhile ago from the Candian government that said most minorities, including South Asians, Chinese, and Afro-Caribbeans had low Vitamin D levels due to lack of sun exposure.

    This should be more true the further South you get. I would imagine Southern Florida would be fine, but New York? Boston? Phili?

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  4. Slaves had poor nutritional status during all stages of life because of the inadequate dietary intake accompanied by high energetic costs of physical work and infectious diseases.


    The consensus has been against this view since the 1970s:

    "In 1974, he and Stanley Engerman published an exhaustive study of slave economics entitled “Time on the Cross.” Historians had long insisted that slavery was not only inhuman; it was bad business—hungry, brutalized workers made the poorest of farmers. Fogel and Engerman found nearly the opposite to be true: Southern plantations were almost thirty-five per cent more efficient than Northern farms, their analysis showed. Slavery was a cruel and inhuman system, but more so psychologically than physically: to get the most work from their slaves, planters fed and housed them nearly as well as free Northern farmers could feed and house themselves.

    US slaves were taller than the average person in every European country, which anthropometric historians take as an index of health. Europeans should be the ones with low birth weight babies.

    Low birth weight is a common feature of African and African diaspora populations. This paper shows the B-W disparity is the same in England as in the US, and lists numbers for some other black nations:

    % Low Birth Weight:

    England (W) 5.2%
    US (W) 4.6%
    England (B) 11.3%
    US (B) 10.4%
    Barbados 7-9%
    Antigua 7-9%
    Jamaica 7-9%
    Trin&Tob 23%
    Senegal 18%
    Chad 17%
    Nigeria 14%
    Mozambiq 14%
    Kenya 11%

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  5. MORE:

    Haitian-American: 8.2%
    Nigerian-American*: 7.1%
    Cuban blacks**: 9.9%
    Brazilian bk**: 8.9%
    S+C Amer bk**: 6.1%
    African black**: 6.7%
    Europe blacks**: 7.0%
    Asia blacks**: 8.3%
    Puerto Rico bk**: 8.2%



    * This study curiously considers this number (well within the range of the other inflated numbers listed here) evidence against a genetic hypothesis. Though the authors readily admit African immigration is highly nonrepresentative: "The high educational level of African-born black women in Illinois indicates that rigorous selection occurs among African immigrants and suggests an overrepresentation of women born into affluent families, an elite subgroup in any developing nation."

    ** US blacks by national ancestry

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  6. Furthermore higher birth weights appear to be an environmental, and possibly genetic adaptation to higher latitudes. The correlation between birth weight and national latitude in Europe is .75. And the correlation between birth weight and state latitude in the US is 0.44 for whites and 0.18 for blacks.

    This is very interesting because IQ increases in the same manner with latitude for both whites and blacks in the US and for nations and regions within Europe. And higher birth weights are significantly correlated with higher IQs.

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  7. Abstract 2 says: African Americans not only suffer from a disproportionate burden of CVD relative to whites, but also have higher rates of the perinatal health disparities now known to be the antecedents of these conditions.

    Yan Klimentidis mentions also today that: Previous research has found that African ancestry is associated with healthier lipid profiles, compared to European ancestry, and that people of African descent in the UK have lower coronary heart disease compared to whites.

    Paradox that I think it's caused because US Afroamericans have suffered major bottlenecks in slavery period (so they are not representative of blacks around the world, in spite of their mostly West/Middle African ancestry). Unlike in other colonial areas, the flow of slaves into the USA was eventually cut and replaced by local "breeding". Instead in Africa the genetic pool was always much wider, and that also probably applies to the Caribbean and Brazil where slaves were arriving all the time from Africa until abolition.

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  8. Birth weights in Africa are influenced by adverse economic conditions (poverty/malnutrition) that are lacking in most of the rest of the world.

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  9. The correlation between birth weight and national latitude in Europe is .75.

    was in the 50s and 60s is more like it. A lot has happened in the anthropometry of Europeans since.

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  10. This comment has been removed by the author.

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  11. Dragon Horse,

    Perhaps this article might be of some interest to you: http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1695156

    According to the abstract, "OBJECTIVES. The purpose of the study was to determine the role of infant race as a determinant of the Black-White disparity in low birthweight (< 2500 g). METHODS. Univariate analysis and multivariate logistic regression were performed on Illinois vital records from 1982 and 1983 and on 1980 United States census income data. RESULTS. Fourteen percent of the infants born to Black mothers and White fathers were of low birthweight, compared with 9% of infants born to White mothers and Black fathers and 6% of a random sample of White infants. Both groups of biracial infants were more likely to have been born to unmarried mothers and to reside in very low-income (< $10,000 per year) census tracts than were White infants. When all confounding variables were entered into a logistic model, the adjusted odds ratio of low birthweight for biracial infants born to Black mothers and White fathers equaled 1.4. When biracial infants born to White mothers and Black fathers were compared with White infants, the adjusted odds ratio of low birthweight equaled 1.0. CONCLUSIONS. Paternal and consequent infant race does not affect the birthweight distribution of those born to White mothers and Black fathers. Unidentified factors closely related to maternal race underlie the Black-White disparity in infant birthweight."

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  12. was in the 50s and 60s is more like it.

    The birth weight data in that paper is from 1980. Still that was 30 years ago, and the sample is limited. For a more recent look, here is awesome WHO low birth weight data (PDF) for just about every nation in the world circa 2000.

    Average latitude data is here. Using just the European countries from the earlier paper (N=15), the correlation between latitude and % low birth weight is -.59.

    But using all available European countries (N=36), the correlation is -.41. For comparison, the correlation between latitude and IQ in Europe is 0.35 (N=28).

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  13. Percentage of low birth weight is not the same as birth weight.

    As for the relationship between country IQ and birth weight that you insinuated, the correlation between the two (based on the article you cited and Lynn's IQ data) is -0.29, which isn't supportive of your claim.

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  14. The IQ data wasn't Lynn's, it was my own conversions. But since I haven't put that online yet, let's try this again with viewable data.

    Scores from the g loaded PISA 2006 test are available from the OECD. The low birth weight data is available from the WHO. And, after some sleuthing about, I've found birth weight data (from 2002-2005) on the website of the United Nations.

    1) First off, low birth weight and average birth weight are strongly related as one might suspect from a normal distribution. The correlation is -.81 (N=23).

    2) Second, average birth weight and latitude are strongly, almost perfectly, related: 0.92 (N=23). This is stronger than the .75 relationship WH James found in the data 30 years ago. In accordance with Monsieur Bergmann, babies get bigger as you move north.

    3) Third, cognitive ability increases with latitude. The correlation between latitude and PISA 2006 scores is .50. (N=33)

    4) Finally, average birth weight significantly predicts PISA scores (0.57, N=23), which is, of course, supportive of my comments above.

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  15. And, after some sleuthing about, I've found birth weight data (from 2002-2005) on the website of the United Nations.

    The link to this data is broken in your swivel pages.

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  16. The updated link in your swivel page points to a histogram of birth weights and not to average birth weight.

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  17. Unfortunately Swivel doesn't update graphs, but I added birth weight data for Croatia (N=24), and made minor changes to a few other numbers: Birth weight and PISA, Latitude and PISA, Birth weight and Latitude.

    Birth weight was estimated the same for every country by making a weighted average of the histogram; i.e.:

    Austria

    750 361
    1250 473
    1750 1,189
    2250 3,332
    2750 13,431
    3250 30,030
    3750 22,460
    4250 6,134
    4750 732
    5250 48

    = 3312 grams

    According to William James, this is also how he calculated his numbers from the 1981 UN Demographic Yearbook.

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  18. The correlation between 1981 birthweight and three measures of cognitive ability are:

    Lynn: -0.27
    Buj (1981): -0.11
    PISA 2006: +0.23

    Since the birthweight-cognitive performance correlation which you found isn't stable in a short period of time, this argues against a genetic explanation for it.

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  19. I am a retired MD psychiatrist and am learning about genetics of populations and so, since a short year...
    I am not very cute and competent especially in Stats and Probs!!!!
    But have enough MD experimental attitude ability to be amazed of the lack of serious in samples sizes and stats results with definitive conclusions about topics of which the complexity is uncommensurable...!
    Are all these "scientists" Propagandists (like a Beghar)or Narcissists? to conclude like the famous joke of that British who,landing in Calais and seing a red haired lady concludes all French women are red haired!

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