That's all folks

In 1786, estimates placed our average life expectancy at just 24 years. A hundred years later (1886) it had doubled to 48 years. Not too impressive.

If you are born today you might expect to live to a ripe old age of 76. This assumes that we continue to see the improvements in life expectancy that we have seen over the last centuary. However, according to some we are looking over the precipice that is a revolution in lifespan modification. With recent discoveries, many pundits predict that life expectancy will continue into triple-digits. In fact, as we address the maladies of old age and the process of ageing apparently we shouldn't have to die at all in the future. But what does science say? In the last in our brief series taking a snapshot of current development in the science of ageing we mark the conclusion of the clinical phase of the MID-Frail study, which is looking at ways of modifying disease in old age, and also the first phase of the Frailomic initiative, investigating inherent markers for the development of frailty. Both initiatives are funded by multimillion Euro grants from the European FP7 Framework and being run by Niche Science & Technology Ltd.

It is universally agreed that access to sanitation, waste removal, electricity, refrigerators, vaccinations and our constant improvements in healthcare are responsible for increases in our life expectancy. But it is also pushing more and more people into the group defined as ‘elderly’. In some, this is not a concern, the media is filled with stories of 70-year olds running marathons and completing triathlons. But these people are generally anomalies. Most people will eventually become frail. Frailty brings exhaustion, weakness, weight loss and a loss of muscle mass and strength. In addition, the risk of concomitant diseases such as diabetes, dementia and cardiovascular disease increases markedly as we enter our 50s, 60s and 70s. Ageing brings a grim prognosis. When coupled with increases in life expectancy it means that many can expect to spend extended periods experiencing distressing loss of functionality, making it the most problematic expression of population ageing; not to mention the tremendous costs associated with our care as we age.

But let’s not get despondent too quickly, promises of immortality may be a little premature. Several different lines of research suggest that we are programmed to die. In current time frames it seems that John Maynard Keynes was correct when he observed, “we are all dead.”

Mathematical approaches suggest that it isn’t possible to prevent ageing. Previously, it has been proposed that we could somehow eliminate ‘sluggish’ cells that are linked with aging while keeping normal cells ticking along. In theory, this sounds simple but as we age, some cells give up the ghost and stop working whereas others go into a sort of 'overdrive' that can develop into cancer. Our inability to predict how individual cells will react makes it difficult to address each side of ageing simultaneously. Researchers claim that their findings prove that aging is an "incontrovertible truth" and "an intrinsic property of being multicellular." The slow crumbling of our bodies over time is inescapable; according to the math, trying to fix these problems is only likely to end up making the issues worse. So the practical conclusion from this line of research is that science may be able to slow aging, but it cannot be stopped. 

Demographic data also appears to suggest that our days are numered and even that our maximum lifespan has already been attained (possibly in the 1990s). Data from the Human Mortality Database, which contains mortality and population data from more than 40 countries since 1900 show a decline in late-life mortality and increase in average life expectancy over time. When the researchers looked at survival improvements since 1900 for people aged 100 and above, they found that gains in survival peaked at around 100 and then declined rapidly, regardless of the year people were born — indicating that there are diminishing gains in reducing late-life mortality and a possible limit to human lifespan. Looking at maximum reported age at death they focused on people verified as living to age 110 or older between 1968 and 2006 (US, France, Japan and UK data). Age at death for these super-agers increased rapidly between the 1970s and early 1990s but reached a plateau around 1995 — further evidence for a lifespan limit. This plateau occurred close to 1997 — the year of death of 122-year-old French woman Jeanne Calment, who achieved the maximum documented lifespan of any person in history. Researchers concluded that the average maximum human life span is 115 years — a calculation allowing that some rare individuals may live to a maximum of 125 years. This result is similar to that calculated by researchers from at Tilburg and Rotterdam's Erasmus universities who pinned the maximum ceiling for female lifespan at 115.7 years after mining data from some 75,000 Dutch people whose exact ages were recorded at the time of death. Men came in slightly lower at 114.1 years.

Genetic data from animal studies suggest that we did not evolve to live forever. Looking at genes associated with a process called autophagy; this is one of our cells' most critical survival processes that promotes health and fitness in the young but drives the process of ageing later in life. The findings may also have broader implications for the treatment of neurodegenerative disorders such as Alzheimer's, Parkinson's, and Huntington's disease where autophagy is implicated. The researchers show that by promoting longevity through shutting down autophagy in old worms there is a strong improvement in neuronal and subsequent whole body health. Autophagy is nearly always thought of as beneficial even if it's barely working. The data instead show that there are severe negative consequences when it breaks down at which point you are better off bypassing it all together. In young worms for example, autophagy is working properly and is essential to reach maturity but after reproduction, it starts to malfunction causing the worms to age. Researchers have been able to track the source of the pro longevity signals to neurons. By inactivating autophagy in the neurons of old worms they were not only able to prolong the worms life but they increased the total health of the worms dramatically.

Natural selection might be expected to result in individuals with traits which counter ageing and yet we age (obviously). This evolutionary contradiction has been debated and theorised on since the 1800s. It was only in 1953 with the hypothesis of antagonistic pleiotropy (AP), proposed by George Williams, that we derived a rational explanation for how ageing can arise in a population through evolution. It was postulated that natural selection enriches genes promoting reproductive success but overlooks any negative effect on longevity. Importantly, this is only true when those negative effects occur after the onset of reproduction. Essentially, if a gene mutation results in more offspring but shortens life it's fine because more descendants take the parent's genes in a shorter time. As these pro-fitness, pro-ageing mutations are actively selected for an ageing process becomes hard-wired into our DNA. Until recently this theory had only been proven mathematically. Although its implications had been demonstrated in the real world, actual evidence for genes behaving in such as fashion had been lacking.

The reason AP genes hadn't been found before  was probably because it's incredibly difficult to work with elderly animals. However, following a relatively small screen a surprisingly large number of genes were found that seemed to operate in an antagonistic fashion. 

So, whatever the pundits say, without some leap forward in our understanding of the process of ageing, and significant development in how we might address it, everyone alive today will die when their time comes. You can adopt practices that may extend the time you have and how healthy you stay over that time but the inevitable is coming. How long do you think you'll live? Tough question for sure, but science can help you here also. Average life expectancies at birth factors in everybody who dies in childhood and early to mid-adulthood. So at birth today (in a Western society) you may expect to live to 75. If you've lived to your 40s, 50s or 60s, you fall into a more select group of people who've been healthy enough or lucky enough to make it that far. You can get a fair estimate the time you have remaining from online actuaries such as this one here.

In conclusion, it is just one of life's realities that you could live for some time yet – or not very long at all. It's simply not possible to know for sure, make the most of it.