Age-related decline in urine concentration may not be universal: Comparative study from the U.S. and two small-scale societies.

OBJECTIVES: Evidence from industrialized populations suggests that urine concentrating ability declines with age. However, lifestyle factors including episodic protein intake and low hypertension may help explain differences between populations. Whether this age-related decline occurs among small-scale populations with active lifestyles and non-Western diets is unknown. We test the universality of age-related urine concentration decline. MATERIALS AND METHODS: We used urine specific gravity (Usg) and urine osmolality (Uosm) data from 15,055 U.S. nonpregnant adults without kidney failure aged 18-80 in 2007-2012 participating in the National Health and Nutrition Examination Survey (NHANES). We tested the relationship of age on urine concentration biomarkers with multiple linear regressions using survey commands. We compared results to longitudinal data on Usg from 116 Tsimane' forager-horticulturalists (266 observations) adults aged 18-83 in 2013-2014 from Lowland Bolivia, and to 38 Hadza hunter-gatherers (156 observations) aged 18-75 in 2010-2015 from Tanzania using random-effects panel linear regressions. RESULTS: Among U.S. adults, age was significantly negatively associated with Usg (Adjusted beta [B] = -0.0009 g/mL/10 years; SE = 0.0001; p < 0.001) and Uosm (B = -28.1 mOsm/kg/10 yr; SE = 2.4; p < 0.001). In contrast, among Tsimane' (B = 0.0003 g/mL/10 yr; SE = 0.0002; p = 0.16) and Hadza (B = -0.0004 g/mL/10 yr; SE = 0.0004; p = 0.29) age was not associated with Usg. Older Tsimane' and Hadza exhibited similar within-individual variability in Usg equivalent to younger adults. DISCUSSION: While U.S. adults exhibited age-related declines in urine concentration, Tsimane' and Hadza adults did not exhibit the same statistical decline in Usg. Mismatches between evolved physiology and modern environments in lifestyle may affect kidney physiology and disease risk.

Inequality in social rank and adult nutritional status: evidence from a small-scale society in the Bolivian Amazon.

Research on the social determinants of health has highlighted (a) the adverse effects of social inequality on individual health and (b) the association between individual social rank and health. In this paper, we contribute to the growing literature on the health consequences of social inequalities by assessing the association between village level inequality in social rank, a form of non-material inequality, and indicators of nutritional status. We use quantitative survey information from 289 men (18+ years of age) from a society of forager-farmers in the Bolivian Amazon (Tsimane'). We construct village level measures of non-material inequality by using individual measures of men's positions in the village hierarchy according to prestige (or freely conferred deference) and dominance (or social rank obtained through power). We find that village inequality in dominance, but not village inequality in prestige, is associated with short-term indices of individual nutritional status. Doubling the coefficient of variation of dominance in a village would be associated to a 6.7% lower BMI, a 7.9% smaller mid-arm circumference, and a 27.1% smaller sum of four skin folds of men in the village. We also find that once we decouple individual social rank based on dominance from individual social rank based on prestige, only prestige-based social rank is associated with nutritional status. Potential explanations for our findings relate to the differential forms of resource access derived from the two forms of social hierarchies and to the social and psychological benefits associated with prestige versus the social costs and psychological stress generated by dominance.

Social rank and adult male nutritional status: evidence of the social gradient in health from a foraging-farming society.

Research with humans and non-human primate species has found an association between social rank and individual health. Among humans, a robust literature in industrial societies has shown that each step down the rank hierarchy is associated with increased morbidity and mortality. Here, we present supportive evidence for the social gradient in health drawing on data from 289 men (18+ years of age) from a society of foragers-farmers in the Bolivian Amazon (Tsimane'). We use a measure of social rank that captures the locally perceived position of a man in the hierarchy of important people in a village. In multivariate regression analysis we found a positive and statistically significant association between social rank and three standard indicators of nutritional status: body mass index (BMI), mid-arm circumference, and the sum of four skinfolds. Results persisted after controlling for material and psychosocial pathways that have been shown to mediate the association between individual socioeconomic status and health in industrial societies. Future research should explore locally-relevant psychosocial factors that may mediate the association between social status and health in non-industrial societies.