This article examines evidence for elevations in basal metabolic rate (BMR) among indigenous Northern (circumpolar) populations and considers potential mechanisms and the adaptive basis for such elevations. Data on BMR among indigenous (n = 109 males; 122 females) and nonindigenous (n = 15 males; 22 females) circumpolar groups of North America and Siberia are compiled and compared to predicted BMRs based on three different references: body surface area (Consolazio et al., 1963), body mass (Schofield, 1985), and fat-free mass (Poehlman and Toth, 1995). Regardless of which reference is used, indigenous circumpolar groups show systematic and statistically significant elevations in BMR ranging from +7% to +19% above predicted values for indigenous men and from +3 to +17% for indigenous women. Nonindigenous males also show elevations in BMR, although not to the same extent as in indigenous men (deviations = +3 to +14%), whereas nonindigenous females show no clear evidence of elevated BMRs (deviations = -7 to +5%). This pattern of variation between indigenous and nonindigenous groups suggests that both functional and genetic factors play a role in metabolic adaptation to northern climes. Recent studies on the ecology and genetics of thyroid function offer insights into the mechanisms through which indigenous circumpolar populations may regulate metabolic rates. Studies of seasonal variation in thyroid hormone levels suggest that indigenous circumpolar populations may have a greater capacity to elevate BMR during severe cold than nonindigenous groups. Recent twin studies indicate a significant genetic component of thyroid responses to environmental stressors. Further research exploring the genetics of seasonal variation in thyroid function and BMR among circumpolar groups would advance understanding of the role that selection may have played in shaping metabolic variation.
Article Archive: Mosher MJ
Over the last 20 years, obesity and associated metabolic diseases have emerged as major global health problems. Among urbanizing populations of developing regions of the world, childhood undernutrition often coexists with adult overnutrition, a phenomenon known as the "dual nutritional burden". A recent work (Frisancho 2003: Am J Hum Biol 15:522-532) suggests that linear growth stunting in early childhood may contribute to adult obesity by reducing the body's ability to oxidize fat. We test central aspects of this model drawing on data from 112 adult Buryat herders (53 males; 59 females) from Southern Siberia. The results are consistent with the predictions of the model, but only for women. Shorter Buryat women (height-for-age Z-scores < or = -1) have significantly lower fasting fat oxidation levels compared to their taller counterparts. Shorter women are also significantly heavier and fatter, and have higher serum lipid levels. Among all Buryat women, reduced fat oxidation is significantly correlated with percent body fatness, serum triglyceride levels, and serum leptin levels, after controlling for relevant covariates. Additionally, Buryat women with high dietary fat intakes and low fat oxidation are significantly fatter and have higher lipid and leptin levels than those with low fat intakes and high fat oxidation. These results suggest that developmental changes in fat oxidation may play a role in the origins of obesity among populations with high rates of linear growth stunting. Further longitudinal research is necessary to elucidate the pathways through which early-life undernutrition may increase risks for adulthood obesity and cardiovascular disease.
Hypertension is an important global health issue and is currently increasing at a rapid pace in most industrializing nations. Although a number of risk factors have been linked with the development of hypertension, including obesity, high dietary sodium, and chronic psychosocial stress, these factors cannot fully explain the variation in blood pressure and hypertension rates that occurs within and between populations. The present study uses data collected on adults from three indigenous Siberian populations (Evenki, Buryat, and Yakut [Sakha]) to test the hypothesis of Luke et al. (Hypertension 43 (2004) 555-560) that basal metabolic rate (BMR) and blood pressure are positively associated independent of body size. When adjusted for body size and composition, as well as potentially confounding variables such as age, smoking status, ethnicity, and degree of urbanization, BMR was positively correlated with systolic blood pressure (SBP; P < 0.01) and pulse pressure (PP; P < 0.01); BMR showed a trend with diastolic blood pressure (DBP; P = 0.08). Thus, higher BMR is associated with higher SBP and PP; this is opposite the well-documented inverse relationship between physical activity and blood pressure. If the influence of BMR on blood pressure is confirmed, the systematically elevated BMRs of indigenous Siberians may help explain the relatively high blood pressures and hypertension rates documented among native Siberians in the post-Soviet period. These findings underscore the importance of considering the influence of biological adaptation to regional environmental conditions in structuring health changes associated with economic development and lifestyle change.