Very cool paper, Adaptations to Climate in Candidate Genes for Common Metabolic Disorders (Open Access):
The human species inhabits a wide geographical range encompassing a diversity of climates, and adaptation to these climates likely played an important role in shaping genetic and phenotypic variation among populations. We hypothesized that spatially varying selective pressures related to climate shaped the frequencies of genetic variants in the energy metabolic pathway. To test this hypothesis, we examined patterns of genetic variation in 82 candidate genes for common metabolic disorders across the 52 globally dispersed populations of the Human Genome Diversity Project. We applied a combination of statistical approaches to test whether the geographic distribution of these variants could be accounted for by differing climates, consistent with a signal of spatially varying positive selection. For several climate variables, we observed signals in excess of that expected from human population history and chance alone. Significantly, many of these signals were from genes previously shown to affect cold tolerance and disease risk. Our results provide evidence that variation among human populations in susceptibility to common metabolic diseases may be due, in part, to different histories of selective pressures on genes in these disease pathways. Furthermore, our results point to additional genes and variants that are suitable targets for follow-up disease association studies.
A physical anthropologist once told me that American military research showed that African American soldiers dealt less well with extreme cold than those of European ancestry. In Albion's Seed: Four British Folkways in America, David Hackett Fisher recounts how black slaves in New England suffered higher mortality rates due to a host of respiratory ailments. Granted, one could observe that slaves likely lived at suboptimal conditions, but in the lowlands of the Atlantic coast their mortality rates due to disease were far less of an issue despite generally harsher treatment. So we know the general outline of this; the great thing about genetics is that it can help us figure out the nuts & bolts.
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Could it not be the cold as much as vitamin D deficiency at higher latitudes? There is a high correlation between latitude and temperature (although not perfect, as Seattle is far warmer than Boston in the winter although about the same latitude).
A couple years ago, a black baseball couch caused a mild stir when he said something along the lines of, "Let's be honest, black do better in heat than whites do." I bring it up, because I recall someone mentioning that Army studies actually showed that black recruits were more likely to suffer heat stroke than whites. It was proffered that this could be psychological, i.e. whites are more likely than blacks to think they are in danger of heat stroke and hydrate properly.
Just another data point.