Addressing a much-debated question about the impact of stress on survival in wild, nonhuman primates, a new multi-decadal study involving 242 wild female baboons found evidence to support chronic stress as a significant factor affecting survival. The study found that a female baboon with a stress response - as reflected in fecal glucocorticoid concentrations, a biomarker of stress response - in the top 90% for her age throughout adulthood was expected to lose 5.4 years of life compared to a female with glucocorticoid concentrations in the bottom 10% for her age group. The findings, which leveraged more than 14,000 fecal glucocorticoid measurements over a total of more than 1,600 years of female adult lifespan, support that these stress response measurements may be strong predictors of survival in female baboons. The results could also help explain why some nonhuman primate individuals, as well as humans, live longer than others. Scientists have debated whether differences in chronic activation of the hypothalamic-pituitary-adrenal (HPA) axis (the stress response) during adulthood are tied to individual differences in survival. Previous research on humans has shown that factors such as social isolation and low socioeconomic status are associated with elevated glucocorticoid levels from increased HPA axis activation, and further research has found that chronically elevated glucocorticoid levels can lead to health problems such as cardiovascular disease and diabetes. However, evidence for the link between chronic stress and detrimental health effects in non-human primates had not been previously identified in natural animal populations. To close this research gap, Fernando Campos and colleagues measured and analyzed 14,173 fecal glucocorticoid measurements from adult female baboons living in the Amboseli ecosystem in Kenya, over the course of their entire adult (>5 years old) lives. They chose to use fecal measurements because they are more stable than those from blood or plasma, reflect concentrations over several hours rather than at one instance, and are not altered by restraint or handling. The researchers then developed models to test the links between longevity and lifelong high glucocorticoid levels as opposed to increases in glucocorticoids associated with discrete events and specific conditions (such as dominance rank, group size, pregnancy, and lactation). The authors observed greater differences in life expectancy between those individuals with high- and low- fecal glucocorticoid measurements in the cumulative effect model than in a current value model, the latter of which illustrated a spike in concentrations prior to death caused by trauma or illness. The findings suggest that high stress levels throughout adult life affect survival, not just high stress levels close to the time of an individual's death. Campos et al. note that the effects of chronic stress on the survival of adult female baboons are robustly linked to those of social isolation and early-life adversity, as they are in humans.
