Height, Health Care and I.Q.

On a good day, I’m 5′ 7″. (I prefer to think of myself as compact but made of premium materials.) That makes me about the same height as economist John Komlos of the University of Munich, who is at the heart of Nancy Shute’s recent NPR report about how Americans’ stable stature may reflect reflect shortcomings of its healthcare:

Through most of American history, we’ve been the tallest population on the planet. Americans were two inches taller than the Englishmen they fought in the Revolutionary War, thanks to abundant food and a healthy rural life, far from the disease-ridden cities of Europe.

But we’re no longer at the top. Northern Europeans are now the world’s tallest people, led by the Dutch. The average Dutch man is 6 feet tall, while the average American man maxes out at 5-foot-9.

Good health care and good nutrition during pregnancy and early childhood are two reasons why the Dutch have grown so tall, Komlos says. In addition, the Dutch guarantee equal access to critical resources like prenatal care. That’s not the case in the United States, where 17 percent of the population has no health insurance.

When I first heard the suggestion that economic inequality and inadequacies of health care in the U.S., my skepticism antennae went up. Surely it couldn’t be that simple, I thought. After all, the past few decades have seen a big influx of immigration to the U.S. from Latin America and Asia; perhaps incoming shorter populations were masking growth in U.S. stature that would otherwise be apparent.

But that is not the case. Shute’s article was anticipated in 2004 by Burkhard Bilger’s fantastic article in The New Yorker, which is vastly more thorough (natch!) and anticipated exactly this objection—as, one would hope, Komlos himself would and did:

The obvious answer would seem to be immigration. The more Mexicans and Chinese there are in the United States, the shorter the American population becomes. But the height statistics that Komlos cites include only native-born Americans who speak English at home, and he is careful to screen out people of Asian and Hispanic descent. In any case, according to Richard Steckel [of Ohio State], who has also analyzed American heights, the United States takes in too few immigrants to account for the disparity with Northern Europe.

By all means, read Bilger’s New Yorker piece in its entirety, which makes the case for simple height measurements as an indicator of populations’ average health and explains some of the fascinating insights it offers into the roller-coaster history of Northern European size (which plummeted from the time of Charlemagne until the 17th century, then started upward again), the treatment of slaves on American plantations, and the effects of industrialization worldwide. Even if you’re still leery (as I am) about using height this way—and about the meaning of the U.S.-Dutch comparison in particular—you’ll find the story provocative and rewarding.

Let me break out one particular point in Bilger’s article because of how it illuminates another, even more contentious issue: intelligence. Bilger writes:

In the nineteenth century, when Americans were the tallest people in the world, the country took in floods of immigrants. And those Europeans, too, were small compared with native-born Americans. Malnourishment in a mother can cause a child not to grow as tall as it would otherwise. But after three generations or so the immigrants catch up. Around the world, well-fed children differ in height by less than half an inch. In a few, rare cases, an entire people may share the same growth disorder. African Pygmies, for instance, produce too few growth hormones and the proteins that bind them to tissues, so they can’t break five feet even on the best of diets. By and large, though, any population can grow as tall as any other.

What’s noteworthy about this observation that the varying heights of populations are not limited primarily by their genetic differences is that the best estimates peg the heritability of height at around 80 percent. That is, within a population in a consistent environment, 80 percent of the variation in height owes to genetic factors. (Or if you prefer, your parents’ height was 80 percent predictive of your own because their height suggested how much your height might vary from the mean.) In the case of height, those genetic factors are still rather obscure—a Nature Genetics paper published last summer suggested that tiny nudges might be scattered throughout the genome rather than concentrating within a few clearly identifiable “tallness” or “shortness” alleles. But whatever the case, two facts are undeniable: (1) a genetic signal in height is undeniable, and (2) environmental influences can swamp—not erase, but overwhelm—the variation otherwise attributable to genetics, which is why the traditionally short Japanese are nearly the height of Americans now and we are nine inches taller than the Frenchmen who stormed the Bastille.

Remember this the next time you read about the genetics of I.Q. and the arguments that are framed around differences in intelligence between races or other population groups. The heritability of I.Q. can be hard even to define (read this lengthy but worthwhile post by Cosma Shalizi to understand why) but good estimates often place it at around 50 percent—well below that of height. Environmental influences on I.Q. should therefore be huge, and one should be very skeptical of arguments that imply (or state outright) that any alleged differences between those groups are innate or unchangeable. Indeed, if Komlos and his colleagues are right that differences in health care explain the plateau in U.S. height, one might expect that those same health care differences—which certainly correlate with economic status and race in this country—could have a very marked effect on I.Q., too.

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39 Responses to Height, Health Care and I.Q.

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  2. mark says:

    Given the obesity numbers, perhaps Americans are just expanding horizontally and not vertically.

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    • MaryR says:

      Actually, twin studies have shown that weight is about 70% heritable, compared to the 80% for height.

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  3. matt says:

    A few things,

    1. You are correct that its very hard to disentangle within population variance and between population variance.
    2. However, its not that difficult. In the US Blacks are on average 2cm taller than whites. Perhaps they would be even taller without health-care disparities, however the between race disparity would then be likely larger.
    3. Sudanese Nilotes are taller than the dutch, but they are not a country the arabs in north bring down the average. No one would say they have access to good health care, or adequate food.
    4. In the last 40 years racism and hunger have markedly decreased in the US, it would be interesting to compare average heights for the two groups and average IQs from the passage of the civil rights act and great society programs to today.
    5. There are other things going on than healthcare/Nutrition and genetics. A back of the envelop calc 1/5 of the IQ difference can be explained by different rates breast feeding. Whites are much more likely to breast feed. There is a gene that about 90% of all people have that gives you 7 IQ points if your breast feed. The Dutch btw have rates that are about 4% higher than the US total rates for breastfeeding. Also US rates have really increased in the past 20 years, while the dutch rates are higher. Interestingly breastfeeding has no effect on height. http://www.physorg.com/news113505546.html

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    • Douglas Knight says:

      Randomized controlled studies of breastfeeding show no effect on IQ. I’m not impressed by the study in which 300 children without the gene showed no effect, while the other 3000 showed the usual spurious correlation.

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  5. Careless says:

    And then someone at Marginalrevolution links this:

    http://www.cbs.nl/nl-NL/menu/themas/gezondheid-welzijn/publicaties/artikelen/archief/2008/2008-2367-wm.htm

    Which is sort of a problem for your thesis

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  7. Winston McGrain says:

    “Remember this the next time you read about the genetics of I.Q. and the arguments that are framed around differences in intelligence between races or other population groups.”

    I thought it was anathema to suggest that there were detectable differences in I.Q. between races or other population groups at all. Why would environment have an impact on something that supposedly doesn’t exist anyway?

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  8. Peter Schaeffer says:

    If the greater height of Dutch people could be explained by superior health care, then we should expect to find at least two other things to be true.

    1. The children of high income Americans should be at least as tall as the Dutch, because they (presumably) have sufficient access to health care.

    2. The correlation between height at the start of adulthood and income should be very strong with lower income folks (with presumably less access to health care) being much shorter than high income young adults.

    As it turns out, neither statement is true. Check out THE HEIGHT OF US-BORN NON-HISPANIC CHILDREN AND ADOLESCENTS
    AGES 2-19, BORN 1942-2002 IN THE NHANES SAMPLES
    John Komlos
    Ariane Breitfelder
    Working Paper 13324
    http://www.nber.org/papers/w13324

    Note that a correlation between income and height does exists. However, it is not nearly large enough to explain the 3 inch height difference between men in the U.S. and The Netherlands.

    Thank you

    Peter Schaeffer

    P.S. Note that the paper was written by Komlos and Breitfelder.

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    • brendan says:

      Your first hypotheses would only be correct if the quality of health care that high income Americans receive is equal to the quality of health care that the dutch receive. I don’t think you can just assume that’s true.

      Your second hypothesis seems to be non-falsifiable. Komlos and Brietfelder say “We find the expected positive correlation between height and family income” but you say, without explanation, that the second hypothesis has been proven untrue. Why? What is the threshold for “very strong?”

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      • Peter Schaeffer says:

        Brendan,

        If you spend anytime reading the debates about health care in the United States, you will see that there is a broad consensus that, at the high-end, American health care is the “best in the world”. The public policy debate is about the health care received by the poor and uninsured. Of course, the cost of the system is also an issue.

        However, no one claims that the health care (specifically including prenatal care) received by upper income Americans is inferior. To assert that it is so inferior (with no supporting facts) that it can account for the inferior (shorter) stature of upper income Americans (versus the Dutch average) is stretching the truth far beyond the breaking point.

        Of course, the second hypothesis is untrue. Follow the link I provided and read the Komlos and Breitfelder paper. To get you started, let me quote from Komlos and Breitfelder.

        “The income effect is estimated by the function f3 (Figure 6). As one would expect height increases with income in most range of income and the effect is substantial; the difference is about 0.4-0.5σ between the poor and the rich.”

        σ is the symbol used by the authors for 1 standard deviation. The standard deviation of male height in the United States is 2.5 inches. Figure 6 in the K & B paper shows that high income boys are 0.2σ taller than average. That is 0.5 inches.

        The author (Rennie) asserts that Dutch men are 3 inches taller than their American counterparts. Given that high income American boys are still 2.5 inches shorter than the Dutch average (and even shorter than high income Dutch boys), it should be clear that non-health care factors are at work here.

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  9. Roy says:

    The answer is milk consumption. Height and milk drinking are very tightly connected. Even those Sudanese Nilotes, are heavy milk consumers, much more so than the Arabs.

    In the US this is not as high in the Netherlands, and in Japan it has been rising very rapidly in children and pregnant mothers, even with the high incidence of lactose intolerance.

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  10. adam says:

    Because I do not expect Rennie to come back to this, I decided to cross-post from Marginal Revolution:
    ———————————————————————————————–
    Easily falsifiable [theory]:

    In the Netherlands, average adult height has a beautiful cline (relation) with latitude: differences between the southern (shortest) and northernmost (tallest) provinces were 2.1cm for men and 2.4cm for women in 2006 (second graph). North-south distance between these two areas is ~200km (150miles).

    This in a small country, where incomes in these areas are the same, and slightly lower than the central part of the Netherlands, and where the healthcare system is exactly the same.
    ——
    Why do people like [Rennie] keep on flogging this dead horse?
    Obama won, and gave [him] the healthcare system he wanted, which will not lead to taller nor longer-living people – because these are more influenced by genes than by the difference in health care reimbursement – but will lead to waiting lists, lower quality of care and I predict higher mortality from cancer.

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  11. Frank says:

    I never drank milk–blech–and am tall for my cohort!

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  13. JL says:

    Around the world, well-fed children differ in height by less than half an inch

    which is why the traditionally short Japanese are nearly the height of Americans no
    w

    That’s simply BS. Look here: http://en.wikipedia.org/wiki/Human_height#Average_height_around_the_world. In 2006, Japanese 19-year-olds were two to three inches shorter than Europeans and North Americans.

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  14. JL says:

    but good estimates often place it at around 50 percent—well below that of height

    The heritability of IQ increases linearly with age: http://www.nature.com/mp/journal/v15/n11/full/mp200955a.html. The 50 percent figure is an average comprising mostly of studies on children. In adults, the heritability of IQ is as high as that of height.

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  15. HelloAll says:

    The Dutch are tall, but when you look into the actual statistics, their height data is self-reported, while most other average height data is based on actual medical measurements (this is true for the U.S. I know for sure). Not saying the Dutch aren’t on average taller, but I’d like to see scientific data instead of them asking the population how tall they are.

    Also, apart from that important fact, why is it that they compare the self-reported Dutch average height of their young people against the measured American average for ALL adults? When you compare the young cohorts of each the difference is 5’10″ for Americans and 6’0.5″ for the Dutch. When you compare the average of all the adults 20+ in each country you get a little over 5’9.5″ for American adults and 5’11″ for Dutch adults. And, again, the Dutch heights are self-reported.

    The Dutch are surely some of the tallest in the world as a nation, but I do think it gets exaggerated just a bit.

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    • Jaap says:

      Not really. I am Dutch, and I am 191 cm. ( 6′ 3.25″) tall.

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      • HelloAll says:

        And? What is your anecdotal evidence supposed to mean in face of fact?

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    • Niknak says:

      If you don’t believe Dutch people are tall go there!

      I am British and 6’6″ but when I went to Amsterdam for a few days I did not feel especially tall!

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      • HelloAll says:

        And? What is your anecdotal evidence supposed to mean in face of fact?

        Neither of you has brought anything to the conversation beyond anecdotes.

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  17. Steve Sailer says:

    The Dutch numbers are self-reported?

    Wow, well, that answers a lot of questions.

    There are three ways to measure height:

    Self-reported
    Measured in shoes
    Measured without shoes.

    For example, NBA players are measured, but they have the option of choosing with or without shoes. (Most choose with.)

    In America, the federal NHANES study measures in foam slippers, in effect without shoes.

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  20. Cullen Roberts says:

    Epigenetics might introduce a lag. Epigenetic changes caused by prenatal exposure to starvation or disease may take several generations to wear off. This would imply that the Japanese, for example, will completely overcome the lingering effects of WWII malnutrion only in the next two decades or so.

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  21. Rodeo Jones says:

    Will someone please compare the ethnically Dutch in America to their European counterparts before continuing to parrot this claim? (Hint: they are gigantic)

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    • mrrunangun says:

      Americans of Dutch extraction are quite tall from what I can see. The women especially so. In Chicago, the Dutch community has long been associated with Morgan Park Academy so that is one of the few places where a relatively homogeneous population of Dutch-Americans can be found. The girls’ sports teams there are striking for the height of the players. When my daughters’ teams played against them in basketball or softball, the smallest varsity player on MPA was 5’7, only one or two of our little Jewish, Irish, and assorted other ethnicities were as tall as their smaller players. Tall and mostly blond, it was like playing the Hitler Jugend. Other places where you can find concentrations of tall Dutch-Americans are in certain bars and Christian colleges in western Michigan. Maybe still at Augustana college in Rockford, Ill.

      Seen on a popular south side Chicago 1970s bumper sticker, ” you ain’t Dutch, you ain’t much”.

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  22. Roy Frye says:

    There is a well known association between height and IQ which may be mediated via overlapping genetic influences or pleiotropy (see Beauchamp ref below). Also physical growth is mainly mediated through the action of a growth factor called IGF-1 which acts downstream of Growth Hormone in the pathway that regulates height. This same growth factor has been linked to brain growth and development. Interestingly it has been shown that the serum levels of IGF-1 in children are positively correlated with IQ (see Gunnell ref below).

    1. Behav Genet. 2010 Jul 6. [Epub ahead of print]

    On the sources of the height-intelligence correlation: New insights from a
    bivariate ACE model with assortative mating.

    Beauchamp JP, Cesarini D, Johannesson M, Lindqvist E, Apicella C.

    Department of Economics, Harvard University, Cambridge, MA, 02138, USA,
    jpbeauch@fas.harvard.edu.

    A robust positive correlation between height and intelligence, as measured by IQ
    tests, has been established in the literature. This paper makes several
    contributions toward establishing the causes of this association. First, we
    extend the standard bivariate ACE model to account for assortative mating. The
    more general theoretical framework provides several key insights, including
    formulas to decompose a cross-trait genetic correlation into components
    attributable to assortative mating and pleiotropy and to decompose a cross-trait
    within-family correlation. Second, we use a large dataset of male twins drawn
    from Swedish conscription records and examine how well genetic and environmental
    factors explain the association between (i) height and intelligence and (ii)
    height and military aptitude, a professional psychogologist’s assessment of a
    conscript’s ability to deal with wartime stress. For both traits, we find
    suggestive evidence of a shared genetic architecture with height, but we
    demonstrate that point estimates are very sensitive to assumed degrees of
    assortative mating. Third, we report a significant within-family correlation
    between height and intelligence [Formula: see text] suggesting that pleiotropy
    might be at play.

    PMID: 20603722 [PubMed - as supplied by publisher]

    2. Pediatrics. 2005 Nov;116(5):e681-6.

    Association of insulin-like growth factor I and insulin-like growth
    factor-binding protein-3 with intelligence quotient among 8- to 9-year-old
    children in the Avon Longitudinal Study of Parents and Children.

    Gunnell D, Miller LL, Rogers I, Holly JM; ALSPAC Study Team.

    Department of Social Medicine, University of Bristol, Bristol, United Kingdom.
    d.j.gunnell@bristol.ac.uk

    BACKGROUND: Insulin-like growth factor I (IGF-I) is a hormone that mediates the
    effects of growth hormone and plays a critical role in somatic growth regulation
    and organ development. It is hypothesized that it also plays a key role in human
    brain development. Previous studies have investigated the association of low
    IGF-I levels attributable to growth hormone receptor deficiency with intelligence
    but produced mixed results. We are aware of no studies that investigated the
    association of IGF-I levels with IQ in population samples of normal children.
    OBJECTIVES: To investigate the association of circulating levels of IGF-I and its
    principle binding protein, IGF-binding protein-3 (IGFBP-3), in childhood with
    subsequent measures of IQ. METHODS: The cohort study was based on data for 547
    white singleton boys and girls, members of the Avon Longitudinal Study of Parents
    and Children, with IGF-I and IGFBP-3 measurements (obtained at a mean age of 8.0
    years) and IQ measured with the Wechsler Intelligence Scale for Children (at a
    mean age of 8.7 years). We also investigated associations with measures of speech
    and language based on the Wechsler Objective Reading Dimensions test (measured at
    an age of 7.5 years) and the Wechsler Objective Language Dimensions test
    (listening comprehension subtest only, measured at an age of 8.7 years). For some
    children (n = 407), IGF-I (but not IGFBP-3) levels had been measured at
    approximately 5 years of age in a previous study. Linear regression models were
    used to investigate associations of the IGF-I system with the measures of
    cognitive function. RESULTS: Three hundred one boys and 246 girls were included
    in the sample. IGF-I levels (mean +/- SD) were 142.6 +/- 53.9 ng/mL for boys and
    154.4 +/- 51.6 ng/mL for girls. IQ scores (mean +/- SD) were 106.05 +/- 16.6 and
    105.27 +/- 15.6 for boys and girls, respectively. IGF-I levels were associated
    positively with intelligence. For every 100 ng/mL increase in IGF-I, IQ increased
    by 3.18 points (95% confidence interval [CI]: 0.52 to 5.84 points). These
    positive associations were seen in relation to the verbal component (coefficient:
    4.27; 95% CI: 1.62 to 6.92), rather than the performance component (coefficient:
    1.06; 95% CI: -1.67 to 3.78), of IQ. There was no evidence that associations with
    overall IQ differed between boys and girls. In a data set with complete
    information on confounders (n = 484), controlling for birth weight (adjusted for
    gestation), breastfeeding, and BMI slightly strengthened the associations of
    IGF-I levels with IQ. Additionally controlling for maternal education and IGFBP-3
    levels attenuated the associations (change in IQ for every 100 ng/mL increase in
    IGF-I levels: 2.51 points; 95% CI: -0.42 to 5.44 points). The weakening of
    associations in models controlling for markers of parental socioeconomic position
    and education could reflect shared influences of parental IGF levels on parents’
    own educational attainment and their offspring’s IGF-I levels. In unadjusted
    models examining associations of Wechsler Objective Reading Dimensions and
    Wechsler Objective Language Dimensions test scores with IGF-I levels, there was
    no strong evidence that performance on either of these tests was associated with
    circulating IGF-I levels, although positive associations were seen with both
    measures. Associations between IGF-I levels measured at age 5 and Wechsler
    Intelligence Scale for Children scores (n = 407) were similar to those for IGF-I
    levels measured at age 7 to 8. For every 100 ng/mL increase in IGF-I levels at 5
    years of age, IQ increased by 2.3 points (95% CI: -0.21 to 4.89 points).
    CONCLUSIONS: This study provides some preliminary evidence that IGF-I is
    associated with brain development in childhood. Additional longitudinal research
    is required to clarify the role of IGF-I in neurodevelopment. Because IGF-I
    levels are modifiable through diet and other environmental exposures, this may be
    one pathway through which the childhood environment may influence
    neurodevelopment.

    PMID: 16263982 [PubMed - indexed for MEDLINE]

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  23. I’d be inclined to agree with you on this. Which is not something I typically do! I enjoy reading a post that will make people think. Also, thanks for allowing me to comment!

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  24. Allen Roth says:

    The unreliability of these sorts of statistics (heights, IQ, etc.) is notorious. I have been 5 10″ (without shoes) my entire life, with most of my friends occasional comments that I look taller–about 6′ 0.” At my annual physical last year, I asked for my height to be measured; it came in at 5′ 8 3/4″ (without shoes). I could not believe it, so I had it done again, with the same result. What is going on?
    Anecdotally, one can go anywhere. My parents both grew up in poor households, in Hungary in the early twentieth century. There is no way that they could have gotten adequate nutrition while growing up. My mother was 5′ 6″, which is really quite tall for a woman. But that is ONE person. Anecdotal “evidence” is really worthless. Nevertheless, I continue to doubt very strongly almost all statistics of this kind; they cannot be well-founded under any method of which I am aware.

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