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Biomedical subjects

W R Leonard

Publications and source records attributed to W R Leonard.

At least 19 recordsLinked to original sources
PubMed2005

Physical growth and nutritional status of Tsimane' Amerindian children of lowland Bolivia.

This study examines patterns of growth and nutritional status of indigenous Tsimane' children under 9 years of age (n = 199 boys and 210 girls), based on a cross-sectional sample from 58 villages from the Beni Deparment of lowland Bolivia. Compared with US children, Tsimane' children are quite short, with linear growth tracking at or below the US 5th centile in both sexes. The prevalence of low height-for-age ("stunting;" HA Z-scores </=-2) is 52% in boys and 43% in girls. In contrast, weight-for-height in Tsimane' children approximates the US median, with the prevalence of low weight-for-height ("wasting"; WH Z-scores </=-2) being only 4% and 6% in boys and girls, respectively. Tsimane' boys and girls are leaner than their US peers, but their levels of body fatness are not so low as to indicate severe energy stress. Arm muscularity of Tsimane' children is similar to that of their US age peers, and this suggests that they are not experiencing acute protein malnutrition. Variation in measures of nutritional status of Tsimane' children is modestly correlated with village-level differences. Degree of isolation, as measured by distance to urban centers or to primary forest, was not a strong predictor of children's anthropometric status. Rather, in both boys and girls, nutritional status was most strongly associated with number of teachers in the village, a measure of access to education. Comparative analyses indicate that high levels of statural growth stunting are common among indigenous populations throughout lowland South America. This problem appears to be largely attributable to poor dietary quality (diets low in key micronutrients) and high disease loads. Further research is needed to identify the specific causes and potential interventions for the high rates of childhood growth stunting in this region.

Age Distribution↗
PubMed2005

Predictors of C-reactive protein in Tsimane' 2 to 15 year-olds in lowland Bolivia.

Infectious disease is a major global determinant of child morbidity and mortality, and energetic investment in immune defenses (even in the absence of overt disease) is an important life-history variable, with implications for human growth and development. This study uses a biomarker of immune activation (C-reactive protein) to investigate an important aspect of child health among the Tsimane', a relatively isolated Amerindian population in lowland Bolivia. Our objectives are twofold: 1) to describe the distribution of CRP by age and gender in a cross-sectional sample of 536 2-15-year-olds; and 2) to explore multiple measures of pathogen exposure, economic resources, and acculturation as predictors of increased CRP. The median blood-spot CRP concentration was 0.73 mg/l, with 12.9% of the sample having concentrations greater than 5 mg/L, indicating a relatively high degree of immune activation in this population. Age was the strongest predictor of CRP, with the highest concentrations found among younger individuals. Increased CRP was also associated with higher pathogen exposure, lower household economic resources, and increased maternal education and literacy. The measurement of CRP offers a direct, objective indicator of immune activation, and provides insights into a potentially important pathway through which environmental quality may shape child growth and health.

Acculturation↗
PubMed2002

An ecomorphological model of the initial hominid dispersal from Africa.

We use new data on the timing and extent of the early Pleistocene dispersal of Homo erectus to estimate diffusion coefficients of early Homo from Africa. These diffusion coefficients indicate more rapid and efficient dispersals than those calculated for fossil Macaca sp., Theropithecus darti, and Mesopithecus pentelicus. Increases in home range size associated with changes in ecology, hominid body size, and possibly foraging strategy may underlay these differences in dispersal efficiency. Ecological data for extant primates and human foragers indicate a close relationship between body size, home range size, and diet quality. These data predict that evolutionary changes in body size and foraging behavior would have produced a 10-fold increase in the home range size of H. erectus compared with that of the australopithecines. These two independent datasets provide a means of quantifying aspects of the dispersal of early Homo and suggest that rapid rates of dispersal appear to have been promoted by changes in foraging strategy and body size in H. erectus facilitated by changes in ecosystem structure during the Plio-Pleistocene.

Africa↗
PubMed2001

Neandertal energetics and foraging efficiency.

Mechanical interpretations of Neandertal skeletal robusticity suggest extremely high activity levels compared to modern humans. Such activity patterns imply high energy requirements; yet it has been argued that Neandertals were also inefficient foragers. The present study addresses this apparent conflict by estimating energy needs in Neandertals and then evaluating those estimates in the context of energetic and foraging data compiled for contemporary human foragers and nonhuman primates. Energy demands for Neandertals were determined by first predicting basal metabolic rates (BMR) from body weight estimates using human standards developed by the World Health Organization [FAO/WHO/UNU (1985) Energy and Protein Requirements. Report of the Joint FAO/WHO/UNU Export Committee, Geneva: WHO]. Total daily energy expenditure (kcal/day) was then estimated assuming high levels of physical activity (i.e., 2--3 x BMR), comparable to those observed among subsistence-level populations today. These estimates of energy requirements (ranging from 3000--5500 kcal/day) were then used to determine Neandertal foraging efficiency assuming (1) minimal survival-level foraging returns, and (2) daily foraging times longer than those observed among any contemporary foraging group and comparable to a nonhuman primate. Even with these extremely conservative parameters, estimates of Neandertal foraging efficiency (approximately 800--1150 kcal/h foraged) were comparable to those observed among living hunter-gatherers. These results indicate that if Neandertals did have heavy activity levels, as implied by their skeletal robusticity, they would have required foraging efficiencies within the range observed among modern groups. Thus, Neandertals could have been either highly active or poor foragers, but they could not have been both.

Adult↗
PubMed2000

Caretakers, child care practices, and growth failure in highland Ecuador.

Problems for child health have been attributed to child and sibling caretaking. Nevertheless, our data from highland Ecuador suggest an ambiguous relationship between growth failure and the practice of peer care. In a region where levels of chronic undernutrition as measured by stunting exceed 75 percent and fully one-quarter of children under five are underweight, analysis of structured observations of a sample of 28 children reveals no statistical association between growth indices and the practice of older children caring for younger children. Qualitative data, however, indicate that the practice can be a complication in specific cases where children already suffer compromised health. While the advantages or disadvantages associated with particular caretakers appear secondary to the risks attending inadequate diets or the broader environment of rural poverty, the potential for difficulties to emerge from peer care suggests that community day care provides a valuable alternative in this context.

Adult↗
PubMed2000

Distribution of the 3' VNTR polymorphism in the human dopamine transporter gene in world populations.

A polymorphism with a variable number of tandem repeats (VNTR) found in the 3' untranslated region of the human dopamine transporter gene (DAT1) was scored in unrelated individuals drawn from 10 geographically widely dispersed populations in order to assess this marker's usefulness in human population genetics. The populations that were analyzed in this study included 4 indigenous groups of Siberia, natives of North and South America, as well as Caucasian and Oceanic groups, most of which represented small-scale societies. A total of 5 DAT1 alleles were seen overall, but only in one Siberian population, the Altai-Kizhi, were all 5 present, and in the Native Americans of Colombia the locus was monomorphic. The most common allele, DAT1*10, ranged in frequency from 52% in Greeks to 100% in South Americans. The high frequency of the DAT1*10 allele (approximately 90%) among Mongoloid groups of north and east Asia distinguishes them from most Caucasian groups. The presence of the rare DAT1*7 allele in relatively high frequency (approximately 5%) among all Siberian groups suggests a close affinity with north Asian groups, especially Mongolians. The presence of the even rarer DAT1*13 allele in one Siberian population, the Altai-Kizhi, reflects this group's long historical contact with Mongolians. The results demonstrated that the DAT1 VNTR polymorphism is useful in investigating population relationships, and that rare alleles at this locus may be particularly valuable in understanding the extent of genetic affinity between neighboring groups and in situations where admixture is suspected. However, because of both the association and linkage of this VNTR locus with attention-deficit hyperactivity disorder (ADHD) in children, and its highly restricted polymorphism (usually 3 alleles) in most human groups, the possibility of selection constraints on the DAT1 gene cannot be ignored.

Female↗
PubMed1999

The central Siberian origin for native American Y chromosomes.

Y chromosomal DNA polymorphisms were used to investigate Pleistocene male migrations to the American continent. In a worldwide sample of 306 men, we obtained 32 haplotypes constructed with the variation found in 30 distinct polymorphic sites. The major Y haplotype present in most Native Americans was traced back to recent ancestors common with Siberians, namely, the Kets and Altaians from the Yenissey River Basin and Altai Mountains, respectively. Going further back, the next common ancestor gave rise also to Caucasoid Y chromosomes, probably from the central Eurasian region. This study, therefore, suggests a predominantly central Siberian origin for Native American paternal lineages for those who could have migrated to the Americas during the Upper Pleistocene.

Genetic Variation↗
PubMed1999

Nutrition, thyroid function and basal metabolism of the Evenki of central Siberia.

Considerable research has shown that indigenous circumpolar populations have elevated basal metabolic rates (BMR). Such elevations are likely promoted by changes in thyroid hormone levels; however, to date, this link between thyroid function and variation in BMR has not been explicitly demonstrated in an indigenous northern group. Thus, the purpose of this paper is to examine 1) the influence of dietary and nutritional factors on variation in thyroid hormone levels, and 2) the influence of thyroid levels on BMR in a sample of indigenous Siberian herders (the Evenki). Measures of body size and composition, dietary intake, thyroid hormones (total and free T3 and T4), thyroid stimulating hormone (TSH) and BMR were obtained for 60 adult subjects (19 males; 41 females) ranging in age from 18-56 years. Thyroid hormone levels in the Evenki were significantly correlated with measures of dietary intake and body composition. Among men, total T3 levels were positively correlated with body weight and fat-free mass (FFM), and negatively correlated with percent body fat; free T4 levels were positively correlated with dietary energy, protein and fat consumption. Among wo-men, there were no clear associations between body composition and thyroid levels; however, dietary energy and protein intakes were po-sitively correlated with total T4 and free T3 levels, respectively. Variation in thyroid hormone levels was associated with differences in BMR. In both sexes, deviations from predicted BMR were positively correlated with free T4 levels. These results demonstrate a link between thyroid hormones and elevated BMR in an indigenous circumpolar population. Further, they show the importance of dietary and nutritional factors for influencing thyroid function and, in turn, metabolic rates among such northern groups.

Adolescent↗
PubMed1998

Demographic and socioeconomic determinants of variation in food and nutrient intake in an Andean community.

Understanding the sources of variation in a community's diet is vital for development work, as well as being a source of anthropological and cultural insights. Previous surveys in the South American Andes suggest that nutrient deficiencies may be widespread; however, such interpretations have remained tentative since variance in Andean populations' diet has not been thoroughly examined. In this paper we consider the variation in diet due to variation in age, sex, and socioeconomic status and variation attributed to inter- and intraindividual variation in the diet. One to six days of dietary data (mean = 3.1) were collected via 24 h recalls from 221 residents of a small, rural community in highland Ecuador. The contribution of various food groups to the diet varied with land holdings and age but not sex. For example, animal-derived foods contribute more and tubers contribute less to the diet of the households with > or = 5 Ha, and sweets contribute more to the diet of children. The interindividual variation in energy and nutrient intake was low and the intraindividual variation high relative to developed countries. The consequence are twofold. First, because interindividual variability is low, group mean intake can be estimated relatively easily, facilitating group comparisons. Second, because intraindividual variation is high, individual nutrient intake cannot be easily estimated, which will decrease the ability to detect associations between nutrient intake and health measures. This knowledge of the sources of dietary variation can lead to better study and survey designs in the rural Andes and elsewhere in the developing world.

Adolescent↗
PubMed1998

Climatic influences on human body size and proportions: ecological adaptations and secular trends.

This study reevaluates the long-standing observation that human morphology varies with climate. Data on body mass, the body mass index [BMI; mass (kg)/stature (m)2], the surface area/body mass ratio, and relative sitting height (RSH; sitting height/stature) were obtained for 223 male samples and 195 female samples derived from studies published since D.F. Roberts' landmark paper "Body weight, race, and climate" in 1953 (Am. J. Phys. Anthropol. 11:533-558). Current analyses indicate that body mass varies inversely with mean annual temperature in males (r=-0.27, P < 0.001) and females (r=-0.28, P < 0.001), as does the BMI (males: r=-0.22, P=0.001; females: r=-0.30, P < 0.001). The surface area/body mass ratio is positively correlated with temperature in both sexes (males: r=0.29, P < 0.001; females: r=0.34, P < 0.001), whereas the relationship between RSH and temperature is negative (males: r=-0.37, P < 0.001; females: r=-0.46, P < 0.001). These results are consistent with previous work showing that humans follow the ecological rules of Bergmann and Allen. However, the slope of the best-fit regressions between measures of body mass (i.e., mass, BMI, and surface area/mass) and temperature are more modest than those presented by Roberts. These differences appear to be attributable to secular trends in mass, particularly among tropical populations. Body mass and the BMI have increased over the last 40 years, whereas the surface area/body mass ratio has decreased. These findings indicate that, although climatic factors continue to be significant correlates of world-wide variation in human body size and morphology, differential changes in nutrition among tropical, developing world populations have moderated their influence.

Adolescent↗
PubMed1997

Comparative primate energetics and hominid evolution.

There is currently great interest in developing ecological models for investigating human evolution. Yet little attention has been given to energetics, one of the cornerstones of modern ecosystem ecology. This paper examines the ecological correlates of variation in metabolic requirements among extant primate species, and uses this information to draw inferences about the changes in energy demands over the course of human evolution. Data on body size, resting metabolism, and activity budgets for selected anthropoid species and human hunter-gatherers are used to estimate total energy expenditure (TEE). Analyses indicate that relative energy expenditure levels and day ranges are positively correlated with diet quality; that is, more active species tend to consume more energy-rich diets. Human foragers fall at the positive extremes for modern primates in having high expenditure levels, large ranges, and very high quality diets. During hominid evolution, it appears that TEE increased substantially with the emergence of Homo erectus. This increase is partly attributable to larger body size as well as likely increases in day range and activity level. Assuming similar activity budgets for all early hominid species, estimated TEE for H. erectus is 40-45% greater than for the australopithecines. If, however, it is assumed that the evolution of early Homo was also associated with a shift to a more "human-like" foraging strategy, estimated expenditure levels for H. erectus are 80-85% greater than in the australopithecines. Changing patterns of resource distribution associated with the expansion of African savannas between 2.5 and 1.5 mya may been the impetus for a shift in foraging behavior among early members of the genus Homo. Such ecological changes likely would have made animal foods a more attractive resource. Moreover, greater use of animal foods and the resulting higher quality diet would have been important for supporting the larger day ranges and greater energy requirements that appear to have been associated with the evolution of a human-like hunting and gathering strategy.

Animals↗
PubMed1997

The China Productivity Project: results and conclusions.

Experiments were conducted to determine what factors cause variation in individual work output (economic productivity). Forty-five young male Chinese cycle haulers from Beijing were assessed for physiological work capacity, size and body composition, health, nutritional status, cold resistance, household social environment, and motivation. Experiments were conducted in the laboratory as well as under actual working conditions; ethnographic observations were made in the household and on the job during the Beijing winter of 1992. Overall work motivation correlated to actual monthly distance/load measures of productivity the most strongly (r = 0.518), followed by physiological capacity estimated by heart rate:speed ratio during field experiments (r = -0.473). Alcohol consumption (a negative factor), household health, and carbohydrate intake were all moderate predictors. Maximum oxygen uptake showed lower correlation (r = 0.261), and among anthropometric values only relatively long lower legs were predictive (r = 0.298). Since many of these variable categories were relatively independent of each other, multiple regression analysis showed that together they explained 61.6% of the work output variance. Simultaneous prediction by FASEM (LISREL) is also very strong.

Adaptation, Physiological↗
PubMed1997

Underestimation of daily energy expenditure with the factorial method: implications for anthropological research.

Under field conditions, total daily energy expenditure (TDEE) has generally been estimated using time allocation techniques (the factorial method). However, recent work suggests that the factorial method underestimates TDEE relative to newer, more accurate methods such as doubly labelled water (DLW) and heart-rate (HR) monitoring. This study compares estimates of TDEE obtained by the factorial and HR-monitoring methods for a sample of 61 indigenous (Evenki; 17 males, 44 females) and 32 nonindigenous ("Russian"; 10 males, 22 females) subjects from three communities in Central Siberia. Energy expenditures obtained from the two methods were significantly correlated (r = 0.495; P < 0.0001), but the factorial method significantly underestimated TDEE relative to the HR-monitoring technique (8.95 +/- 2.73 vs. 8.25 +/- 1.34 MJ/d; P < 0.005). Interpopulational analyses of data compiled from this and other studies indicate that the factorial method consistently underestimates TDEE relative to DLW and HR monitoring and that the magnitude of underestimation increases with expenditure levels. Indeed, among sedentary populations, factorial estimates of TDEE converge on those of the other methods, whereas at high activity levels the disparity is quite large. These results imply that the daily energy requirements of many subsistence-level populations have been underestimated, thus providing an overly favorable picture of energy balance. Moreover, it is likely that underrepresentation of TDEE is most problematic in rural societies of the developing world which tend to have high activity levels and great risk of malnutrition.

Adolescent↗
PubMed1997

Recent fertility and mortality trends among aboriginal and nonaboriginal populations of central Siberia.

We examine mortality and fertility patterns of aboriginal (primarily Evenki and Keto) and Russian (i.e., nonaboriginal) populations from the Baykit District of Central Siberia for the period 1982-1994. Mortality rates in the aboriginal population of Baykit are substantially greater than those observed in the Russians and are comparable to levels recently reported for other indigenous Siberian groups. Infant mortality rates average 48 per 1000 live births among Baykit aboriginals, three times greater than the Russians of the district (15 per 1000 births) and more than double the rates for Inuit and Indian populations of Canada. Similarly, crude death rates of the Baykit aboriginals are twice as high as those observed in either the Baykit Russians or the Canadian aboriginal populations (13 vs 6-7 deaths per 1000 individuals). Birth rates of the indigenous population of Baykit are higher than those of the Russians (33 vs. 15 births per 1000 individuals) but are comparable to those of Canadian aboriginal groups. Violence and accidents are the leading causes of adult male mortality in both ethnic groups, whereas circulatory diseases have emerged as the prime cause of death in women. The greater male mortality resulting from violence and accidents is a widely observed cross-cultural phenomenon. The emergence of circulatory diseases as a major mortality risk for women, however, appears to be linked to specific lifestyle changes associated with Soviet reorganization of indigenous Siberian societies. Marked declines in mortality and increases in fertility were observed in the Baykit aboriginal population during the mid to late 1980s with the government's implementation of anti-alcohol policies. The decline in mortality, however, was largely erased during the early 1990s, as the region became increasingly isolated and marginalized following the collapse of the Soviet Union. Demographic trends in the Baykit District suggest that because the indigenous groups have become more isolated, many are returning to a more traditional subsistence lifestyle.

Adult↗
PubMed1996

Differences between observed and predicted energy costs at rest and during exercise in three subsistence-level populations.

Estimates of daily energy expenditure are important for many areas of research in human ecology and adaptability. The most common technique for estimating human energy expenditure under field conditions, the factorial method, generally relies on activity-specific energy costs derived from published sources, based largely on North American and European subjects. There is concern that such data may not be appropriate for non-Western populations because of differences in metabolic costs. The present study addresses this concern by comparing measured vs. predicted energy costs at rest and during sub-maximal exercise in 83 subjects (52 males, 31 females) from three subsistence-level populations (Siberian herders and highland and coastal Ecuadorian farmers). Energy costs at rest (i.e., lying, sitting and standing) and while performing a standard stepping exercise did not significantly differ among the three groups. However, resting energy costs were significantly elevated over predicted levels (+ 16% in men, + 11% in women), whereas exercising costs were comparable to predicted values (-6% in men, + 3% in women). Elevations in resting energy needs appear to reflect responses to thermal stress. These results indicate that temperature adjustments of resting energy costs are critical for accurately predicting daily energy needs among traditionally living populations.

Adaptation, Physiological↗