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.

You could expect to live to be 76 years old if you were born today. If life expectancy keeps going up the way it has over the last 100 years, this is what will happen. On the other hand, some say we are on the verge of a change in changing people's lives. Many experts think that life expectancy will continue to rise into the triple digits thanks to new findings. If we can figure out how to stop the diseases that come with getting older, we might not have to die at all in the future [1]. But what does science say? In this last article in our short series that gives an overview of what's new in the study of getting older, we mark the end of the clinical phase of the MID-Frail study [2], which is looking at ways to change diseases that happen in old age, and the start of the Frailomic initiative [3], which looks into genetic markers for the development of frailty. Niche Science & Technology Ltd. oversees both projects and gets funds from the European FP7 Framework worth many millions of euros.

Everyone agrees that better sanitation, trash collection, electricity, freezers, immunisations, and better and better healthcare are all factors that have led to longer life expectancy. But it also means that more and more people are becoming what we call "elderly." This might not bother some people; the news is full of stories about 70-year-olds running races and finishing triathlons. But these people aren't like most people. Most people will get weak over time. When you are frail, you get tired, weak, lose weight, and lose muscle mass and power. Also, as we get older, the chance of getting diseases like diabetes, dementia, and heart disease all at the same time goes up a lot. The outlook is not good as you get older. Along with longer life expectancy, this means that many people will have to deal with frustrating loss of usefulness for long periods of time. This is the most problematic aspect of the ageing population, and it doesn't even begin to cover the huge costs of caring for us as we age [4].

But let's not give up too fast; promises of eternal life might not be quite ready yet. Several types of study point to the idea that we are designed to die. Based on how things are now, John Maynard Keynes was right when he said, "We are all dead."

Based on mathematical methods, it seems like it is not possible to stop getting older [1]. In the past, it was thought that we might be able to get rid of "sluggish" cells that are linked to getting older while keeping healthy cells alive. This seems easy at first, but as we get older, some cells die and stop working, while others go into a state of "overdrive" that can lead to cancer. Because we can't tell ahead of time how different cells will behave, it's hard to deal with all aspects of ageing at the same time. The researchers say that their results show that ageing is "an incontrovertible truth" and "an intrinsic property of being multicellular." As time goes on, our bodies will slowly fall apart. Trying to fix these problems will probably only make them worse, according to the maths. Based on this line of study, we can say that science might be able to slow down ageing, but not stop it [5].

Demographic data also appears to suggest that our days are numbered 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 [6]. 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 limit to our lifespan. 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 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 [7].

Animal genes studies show that we did not evolve to live forever [8]. Taking a look at genes related to a process known as autophagy; this is one of the most important ways for our cells to stay alive and keep us healthy when we're young but speeds up the ageing process as we get older. The results could also change how neurological diseases like Alzheimer's, Parkinson's, and Huntington's are treated, since autophagy is thought to play a role in these conditions. Researchers show that turning off autophagy in old worms makes them live longer and improves neural health, which in turn improves whole-body health. People almost always think that autophagy is good, even if it's not working very well. On the other hand, the numbers show that when it breaks, there are very bad things that happen, so you should just skip it altogether. For example, autophagy works properly in young worms and is needed to reach adulthood. But after breeding, it stops working properly, which makes the worms age. Scientists have been able to figure out where the messages that make neurons live longer come from. Not only were they able to make old worms live longer, but they were also much healthier overall by turning off autophagy in their brains.

People with genes that slow down ageing might be expected to arise through natural selection, but we still age (obviously). Since the 1800s, people have talked about and thought about this evolutionary paradox. In 1953, George Williams came up with the hypothesis of antagonistic pleiotropy (AP), which gave us a good reason for how ageing can happen in a group through evolution. It was thought that natural selection favours genes that help with reproduction but ignores genes that hurt life. This is only true if those bad outcomes happen after reproduction starts, which is very important. Basically, it's okay if a gene change makes more children but shorter lives. This is because more children take their parents' genes faster. As these pro-fitness, pro-aging defects are actively chosen, the process of ageing is hard-wired into our DNA. Up until recently, this idea had only been shown to be true through maths. Even though its effects had been seen in the real world, there wasn't any real proof that genes behaved in this way.

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 [9]. 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 [10].

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.

References

1. Targeting death
2. www.midfrail-study.org
3. www.frailomic.org
4. Immortality - no thanks
5. Nelson P, Masel J. Intercellular competition and the inevitability of multicellular aging. Proc Natl Acad Sci U S A. 2017 Dec 5;114(49):12982-12987.
6. Dong X, Milholland, B & Vijg J. Evidence for a limit to human lifespan. Nature 2016: 538; 257–259.
7. Einmahl JJ, Einmahl JHJ, & de Haan L. Limits to Human Life Span Through Extreme Value Theory. Journal of the American Statistical Association, 2019: 114(527), 1075–1080.
8. Wilhelm T , et al. Neuronal inhibition of the autophagy nucleation complex extends life span in post-reproductive C. elegans. Genes & Development, 2017; 31 (15): 1561.
9. Can-we-stop-ageing
10. Longevity illustrator