Signs that Earlier Physical Prowess has a Longevity Cost in Humans

It is fairly well settled in evolutionary theory that there is a trade-off between short-term development versus longer-term tissue maintenance. Species that mature and reproduce quickly tend to have shorter life spans. This relationship also exists when comparing natural variations between individuals within the same species, and here researchers present evidence for this effect in human populations.

Generalized life history theory postulates a trade-off between development and maintenance explaining the considerable variation of traits like age at maturation, age at first reproductive event, number of offspring, size and lifespan across and within species. It is debated whether the variation in human lifespan can also be explained by such trade-offs. Observational studies in women have shown early and above average fecundity to come at a cost of longevity. The life history of men has no distinct mark of the end of development as menarche in women, but negative correlations between number of offspring and life-span after age 50 have also been reported for males. This could be explained as males invest more in physical strength and growth, which is associated with attractiveness and dominance, two traits important for male fitness.

Professional athletes push their physical performance to the maximum and keep accurate track of these achievements. Consequently, their personal record is an accurate representation of the age of their peak performance. Under the assumption that professional athletes train at maximum intensity, this peak performance is an accurate read-out of the maximal physiological capacity of the individual. Because athletes compete intensely, the rank of peak performances is an accurate comparison of these maximal physiological capacities of athletes. According to theory of life history regulation, the period before the peak performance could be considered as development, while the decline in physical capabilities after setting a personal record is a hallmark of the ageing process.

We used a unique historical cohort of 1055 Olympic track and field athletes from 41 different nationalities from the Olympic Games from 1896 through 1936. Track and field is a large group of similar sports for individual performance where the results are measured on a continuous scale. Technological advancements contribute only little to basic body functions like running, throwing and jumping, which are critically dependent on physical strength and coordination. Athletic games are therefore an ideal group of sports to use in this study. Mean age at personal record was 24.9 years. Mean age at death was 72.1 years. To compare peak performance of athletes from different disciplines and sexes we standardized age at, and rank of the personal record per discipline and sex. Athletes who had a peak performance one standard deviation earlier showed 17-percent increased mortality rates compared to those who reached their personal record later in life. Independent of the age of their personal record, athletes who ranked one standard deviation higher than their peers showed 11-percent increased mortality rates compared to those who were ranked lower.

It is tempting to speculate about the underlying biological mechanisms of this developmental constraint. Some have suggested that growth and subsequently, larger size, result in a body which costs more energy to maintain, explaining the higher pace of ageing. The mTOR pathway, which regulates growth in early life and pace of ageing in late life, is a potential molecular pathway that can explain for the observed trade off. Others have suggested that hormonal regulation of development and maintenance could play a role, as has been observed for the GH-IGF signaling pathway explaining the size-life span trade off in domestic dogs, and the muscle mass-immune competence trade-off mediated by testosterone observed in primates and other species. All mechanistic explanations are plausible and it needs to be studied which pathways are causal, and at which we can intervene to secure longer and healthier lives.

Link: http://dx.doi.org/10.18632/aging.101023

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