I stumbled upon a series of open access review papers today, entitled "The Changing Understanding of Aging," written by a veterinarian for an audience of practitioners largely unfamiliar with the history and present state of aging research. As a consequence it's very readable for the layperson, and it really doesn't matter that the papers are as much focused on the animal kingdom as on human research: at the high level much of what is the case for the mammals we keep as pets is also the case for humans - the same theories apply. Only the details of our biochemistries are different, which does lead to greatly differing life spans and rates of aging, but all proceeding according to much the same fundamental mechanisms.
This is the first of three discussions on emerging views of ageing, its derivation, and ageing-related diseases. To offer a context for the series, this first report briefly reviews several major early and recent theoretical debates. Arguments for and against several well-known ageing theories are presented for their veterinary relevance, including mutation, pleiotropy, reproduction-longevity trade-offs, oxygen metabolism and ageing as a genomically programmed product of natural selection. ... Central ideas of these discussions include why post-reproductive life span is relatively common among animals, the nature of age-related diseases relative to stochastic or programmed origins and the disease-related implications.
This second of three discussions about ageing biology and diseases continues at the level of the organism, examining the relationship among body composition, late life and diseases. ... Sarcopenia is declining mass and strength of skeletal muscle during aging. Healthy humans experience a 20%-40% reduced physical strength during decades 7 and 8. In one study, prevalence of sarcopenia among 883 elderly persons ranged from 13%-24% over the ages 65 to 70 and >50% after the age of 80. ... It is disconcerting that investigators have identified early skeletal muscle mass decline in some humans, with substantial change by decade five. Potential life span implications for individuals in this category need to be monitored by primary care and specialist physicians, and not just by geriatricians. Additional implications are that new studies need to be conducted to establish whether or how subtle mid-life changes in muscle mass and strength can be observed across animal species and what concerns accrue for their health and longevity.
A contentious debate revolves around whether ageing is purely a combined effect of stochastic events on residual programming relating to reproductive robustness, or whether ageing itself is programmed by natural selection. Emerging data indicate that the influence of genetic programming on specific late-life diseases, and even individual tissue pathologies, will probably need to be reconsidered in the light of newer theoretical possibilities.