Externally-resident daughters, social capital, and support for the elderly in rural Tibet.

This paper focuses on assistance that externally-resident daughters provide for their aging parents in rural Tibet, China, to challenge the notion that rapid modernization invariably threatens family-based care systems for the elderly. The authors discuss social and economic changes associated with modernization that have created new opportunities for parents to send daughters out of their natal households in ways that can benefit them in old age. By investing in a daughter's education so she can secure salaried employment, or by helping a daughter establish a small business so she can earn an independent livelihood, the authors demonstrate how some externally-resident daughters represent a novel form of social capital that parents can draw on for social support. Daughters with income and freedom from extended family obligations are now providing elderly parents with (1) leverage against co-resident children who do not treat them well, (2) temporary places of refuge from ill-treatment at home, (3) caretaking services and financial support when they require hospitalization, and (4) financial resources independent of their household which they can use to pursue age-appropriate activities like pilgrimage. The authors conclude that this new form of social capital vested in externally-resident daughters is having a positive impact on the lives of the elderly in rural Tibet.

Higher offspring survival among Tibetan women with high oxygen saturation genotypes residing at 4,000 m.

Here we test the hypothesis that high-altitude native resident Tibetan women with genotypes for high oxygen saturation of hemoglobin, and thus less physiological hypoxic stress, have higher Darwinian fitness than women with low oxygen saturation genotypes. Oxygen saturation and genealogical data were collected from residents of 905 households in 14 villages at altitudes of 3,800-4,200 m in the Tibet Autonomous Region along with fertility histories from 1,749 women. Segregation analysis confirmed a major gene locus with an autosomal dominant mode of inheritance for high oxygen saturation levels, associated with a 10% higher mean. Oxygen saturation genotypic probability estimators were then used to calculate the effect of the inferred oxygen saturation locus on measures of fertility, in a subsample of 691 women (20-59 years of age and still married to their first husbands, those with the highest exposure to the risk of pregnancy). The genotypic probability estimators were not significantly associated with the number of pregnancies or live births. The high oxygen saturation genotypic mean offspring mortality was significantly lower, at 0.48 deaths compared with 2.53 for the low oxygen saturation homozygote, because of lower infant mortality. Tibetan women with a high likelihood of possessing one to two alleles for high oxygen saturation had more surviving children. These findings suggest that high-altitude hypoxia is acting as an agent of natural selection on the locus for oxygen saturation of hemoglobin by the mechanism of higher infant survival of Tibetan women with high oxygen saturation genotypes.

Basal metabolic rate and dietary seasonality among Tibetan nomads.

The results of 51 overnight measurements of basal metabolic rate (BMR) in a sample of pastoral nomads resident permanently in Phala, Tibet Autonomous Region, China, are reported. Past studies demonstrated a culturally driven seasonality of diet, with very low summer and very high winter caloric intake. The study was designed to test the hypothesis that the ability of Phala nomads to subsist on low caloric intake for several summer months without signs of malnutrition is explained by lower summer BMR. However, BMR measurements of 40 nomads 13-69 years of age during the summer and remeasurement of 11 nomads during the winter of 1993 provide no evidence for low summer BMR to compensate for the low summer caloric intake. BMR in both seasons is within the normal range predicted by international equations. The BMR of males does not differ from that of females, and the BMR of females averages 7% higher than predicted. Anthropometric evidence reveals that the Phala nomads accumulate body fat during the winter. It is inferred that this may buffer the summer period of low intake. The pattern of subcutaneous fat accumulation in winter, moreover, may afford slight improvement in physiological cold insulation during the severe winters as a consequence of depositing winter fat on the trunk rather than on the periphery. Thus, the dietary seasonality in Phala is a stress that elicits fluctuation in fat energy stores but not BMR. © 1996 Wiley-Liss, Inc.

High prevalence of excess fat and central fat patterning among Mongolian pastoral nomads.

This paper presents information on body size, body composition, and fat patterning in a sample of 750 pastoral nomads aged 5 to 84 years, native residents of Moost district, Mongolia and evaluates the results from the perspective of morphological adaptation to a cold climate. Mongolian nomad men and children have average BMIs close to the U.S. 25th percentile while women have average BMIs close to the U.S. reference median. The prevalence of excess fatness assessed by the Arm Fat Index rises from 5 to 15% during childhood to 65% or more in each adult age-sex group except women 70+ years. The pattern of fat deposition is markedly central (abdominal) among women and children while it is normally so among men: women and children have a very high ratio of waist-to-hip circumference and children have a moderately high ratio of subscapular-to-triceps skinfold compared with other populations. A body composition favoring centrally deposited fat may be adaptive to a cold stressed population because it would aid in heat production (abdominal fat is thermogenic) and heat conservation (more spherical body size and better insulation) in the age-sex groups that are usually at a thermal disadvantage because of small body size and/or low basal metabolic rate relative to men. © 1992 Wiley-Liss, Inc.