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Ape vertebrae reveal why elderly humans risk spinal fractures
It is well established that the rate of bone loss that occurs with aging is a significant risk factor for spinal fracture in the elderly, and that the underlying risk of osteoporosis is related to peak bone mass and bone strength in adulthood. In this paper from a group of evolutionary biologists, the authors used micro-CT to compare the vertebral structure of human adults aged 20 to 40 with equivalent samples from gorillas, orangutans, chimpanzees and gibbons.
The results showed that human vertebrae at the peak of adult health have less strength, a thinner vertebral shell and a lower trabecular bone volume fraction compared to young adult apes matched for body mass and bone mass. Age-related bone loss occurs in all the species studied, but the lower baseline for humans and the fact that they have the longest lifespan means that humans are uniquely susceptible to spontaneous vertebral fractures in later life. No selection pressure exists to boost bone mass in young adult humans, as these effects only become apparent many years after reproduction is completed.
Editor's comment: It has been proposed that humans are susceptible to osteoporotic fractures because of evolutionary adaptations, particularly bipedalism. In addition to the more porous vertebrae observed in humans compared to apes, modern humans have a longer lifespan, providing more opportunity for age-related bone loss to increase susceptibility to vertebral fractures.
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