The Tsimane’ Health and Life History Project
The Tsimane’ are a population of some 9,000 forager-horticulturalists inhabiting a vast area of lowland forests, and savannas east of the Andes in the Bolivian Amazon. They live in about 80 small villages without running water or electricity, and make a living through swidden agriculture, hunting, fishing, gathering, and occasional wage labor.
The Tsimane’ offer some of the last remaining opportunities to study the effects of kin, culture, and ecology on aging in a small-scale, natural fertility, kin-based, subsistence society, and for this reason have been the focus of study by the UNM-UCSB Tsimane’ Health and Life History Project which began in 2001.
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This joint health and anthropology project aims to understand the impacts of ecology and evolution on the shaping of the human life course. It focuses on health, growth and development, aging, economics and biodemography of small-scale populations of hunter-gatherers and horticulturalists, combining biomedical and anthropological research with medical attention.
The following study by Gurven et al. supports the mounting evidence that chronic vascular disease had little impact on adult mortality for most of human evolutionary history.
Inflammation and infection do not promote arterial aging and cardiovascular disease risk factors among lean horticulturalists
The general health of the Tsimane’ is characterised by their short life expectancy at birth of 54 years (from 1990-2000), high infectious loads and inflammation, with half of documented deaths due to infectious and parasitic disease. Anemia is prevalent and physical growth is stunted, however, they are physically fit and consume a lean diet.
Chronic inflammation is associated with all stages of cardiovascular disease (CVD) in modern, sedentary societies. For the Tsimane’ however, their risk of CVD due to higher lifetime infection and inflammation exposure is expected to be offset by their physical fitness, low adiposity and lean diet.
The study found no evidence of advanced atherosclerosis, with an absence of peripheral arterial disease (PAD) among the entire sample of 258 Tsimane’ adults. Furthermore, PAD increases with age in every investigated population except the Tsimane’, including rural and urban settings in both developed and developing countries. The Tsmiane’ also have low rates of hypertension, increasing with age and peaking at 23.5% for adults >70 years.
These results are consistent with previous reports of low CVD among traditional foraging and small-scale farming populations. Traditional populations often show negligible CVD prior to the adoption of western diets and sedentary lifestyles. Australian Aborigines and Pima Indians now have the highest prevalence of obesity and type 2 diabetes in the world.
Interestingly, obesity, blood lipids, cigarette smoking, disease history and cardiovascular indicators were not significantly associated with Tsimane’ PAD after controlling for age and sex. Over half of Tsimane’ adults show unfavourable HDL levels by American Heart Association standards. Also contrary to expectations, higher WBC and ESR associate with lower blood pressure among the Tsimane’ and CRP is not significant, whereas CRP is a positive predictor of high blood pressure in the US.
A possible hypothesis for these findings may be due to the physically demanding Tsimane’ lifestyle. It is estimated that Tsimane’ men and women age 40-49 expend 850 and 450 kcals/day more, respectively, in physical activity than US adults. Exercise reduces oxidative load in muscle, levels of inflammatory cytokines, systolic blood pressure, macrophage-rich fat and improves insulin sensitivity. In comparison with the Tsimane’, physical activity is extremely low among industrialised populations.
Alternative explanations which merit future investigation include genetic variability, the influence of diet (eg. flavonol-rich citrus fruits) and hypothesised cardioprotective effects of helminthic infection.
This study provides preliminary evidence that the presence of chronic infection and inflammation in a subsistence population does not necessarily predict CVD. The risk factors applicable to westernised populations may not accelerate atherosclerosis in the context of a restricted caloric diet, parasitism, and daily physical activity that maintains low BMI.
References
- Gurven M, Kaplan H, Winking J, Eid Rodriguez D, Vasunilashorn S, et al. 2009 Inflammation and Infection Do Not Promote Arterial Aging and Cardiovascular Disease Risk Factors among Lean Horticulturalists. PLoS ONE 4(8): e6590. doi:10.1371/journal.pone.0006590 [Fulltext]
- Tsimane’ photo by M. Gurven.
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