That we could live forever is a theoretical possibility. At the same time advances in care extend our lives about three "good" years per generation. What are we to make of this? Let's find out.
You know the memes sixty-five is the new 50 or 40, depends on what you might be considering. But lifespan is often given in years, almost 78+ for an average US citizen; down a bit because of how many middle age people have died in the current era from overdosing opioids. But like all summary measures, lifespan doesn’t tell us everything we may want to know.
Most of the gains in our lifespan in the last hundred years has come from the younger end of the spectrum, improving infant, child, and maternal mortality – you can’t grow old if you die young. But selfishly I would ask, how are we doing at my end of the spectrum? A recent paper in the Proceedings of the National Academy of Science provides a very different point of view. Their question was whether there was a limit to lifespan? If there were a limit, more and more deaths would be compressed near the end, creating an increasingly skewed curve as health care protected us until we reached our biologic limit. On the other hand, if lifespan has no clear biologic limit then the general pattern of our lifespan would be maintained, a pattern might be identified, and only the onset of the pattern would vary.
To try and get a handle on that they considered 50 years of life-tables, mortality data for individuals by age and gender. Here is what they found, pink is for women, blue for men.
It is clear that a pattern does exist and that the onset of that pattern has moved to increased age over time. For both women and men, lifespan increased, but the general pattern remained the same. For men, the pattern was more dispersed with more outliers early and late; for women, the pattern was less dispersed and later – all findings consistent with what we know about our lifespan.
But viewed in this manner, we might come to several different insights beyond the gender disparity; for once favoring women over men. The researchers were able to calculate how that pattern moved to advanced years. So for many of my generation, sixty-eight to seventy is the new sixty-five. For our children, the new sixty-five may be seventy-six. We seem to gain about three years per generation. Another valuable insight is that these are gains related to what the researchers call period effects, but we can think of as the times of our life. As we resolve the inequalities of one era, they give way to the inequalities of the next. While the data suggests that our biologic lifespan is theoretically limitless, we have a wealth of practical data that says no one gets out alive.
This period effect, or when we live, should give us pause. First, to appreciate the view from the shoulders of the generations before us. Second, we should recognize that a vocal ignorant minority want us to turn the clock back, let me be clear, I am speaking to the anti-vaxxers who will learn nothing from the return of measles. Finally, for those of us who might look askance when health outcomes are tied to poverty and a lack of opportunity, the data suggests that our lifespan is more effected by our times and circumstances than by any magic genetic quality.
Source: Advancing Front of Old-Age Human Survival PNAS DOI: 10.1073/pnas.1812337115