Ray Kurzweil predicts that in the coming decades the term “life expectancy” will become irrelevant. By then medical advances and nanotechnology will be such effective tools with which to repair our bodies as they break down with age it will be as simple as car repair, changing out old parts for new and getting us back on the road again. Indefinitely. Even without the breakthrough technologies that allow us to regrow organs or reprogram faulty genes technological advances are making their imprint on our longevity. But a puzzling part to the equation has emerged. While humans are in fact living longer lives on average, the oldest age that the oldest people reach seems to be stubbornly and oddly precisely cemented right at 114.

Life expectancy nearly doubled in developed countries over the 20th century. Prior to 1950 the increase was due mostly to a decrease in infant mortality. After the 1950s it was a decline in old age mortality that provided the main life-prolonging force. Improvements to the social and physical environments and breakthroughs in healthcare underlie both phases of mortality decrease. A person born in the US at the turn of the 20th century could expect to live 49.2 years. Their ancestor born in 2003 could reasonably expect to see their 77th birthday. But while average lifespans continue to lengthen, the oldest of the old appear to be encountering a rather powerful limiting factor. As reported recently in Slate, the number of oldest supercentenarians – people 110 and older – has stayed at around 80 over the past few years. And the age at which they die hasn’t changed over the past few decades. Data from japan is used to illustrate this. In 1990 there were 3,000 people 100 or older, the oldest of them being 114. Twenty years later the number of people aged 100 and over had grown to around 44,000, but the oldest was still 114. Robert Young, a gerontologist working for the Guinness Book of World Records, estimates that “the odds of a person dying in any given year between the ages of 110 and 113 appear to be about one in two. But by age 114, the chances jump to more like two in three.”

This phenomenon of everyone getting older but the oldest dying at the about the same age is called “rectangularization of the mortality curve.” A mortality curve tracks the probability that a person will be alive at a certain age. At birth the value is 100%. By year one it begins to slope downward, and around 70s, 80s, 90s it drops at a faster rate. In decades past the curve looked like a ski slope, hitting zero around 114. But the fact that more people are living longer lifts the curve and pushes it to the right so it looks more like a cliff than a ski slope – and more like a rectangle.

During our last Google+ Hangout we got a chance to hang with longevity researcher Aubrey de Grey, author of “Ending Aging” who once proclaimed “the first person to live to 1,000 was probably born by 1945.” We asked him about rectangularization, why it was that the whole ski slope doesn’t just move to the right but instead comes crashing down at around age 114. “This is a fascinating phenomenon and nobody has really much idea of what’s going on. What we do know is that it’s absolutely essential to not jump to conclusions about what’s going on. Time and time again over the decades past demographers have been brutally misled by short-term phenomena, by statistics gathered only over a few years. Blips happen for all manner of impenetrable reasons. In this case we’re talking about people born in a small segment of time, around 1900, and most of them born in particular countries and going through certain types of life they might not have gone through had they been born 20 years previously or 20 years later. There are many factors called ‘cohort effects’ that can cause early life phenomena to have an influence on longevity.”

Bottom line: don’t believe the hype.

“At this point I’m not exactly losing sleep over the phenomenon you’re talking about. I think that we’re probably going to see a resumption of the trend of everything just moving to the right eventually.”

De Grey also adds that medical developments could make rectangularization, much speculated upon in the study of aging, a moot discussion. “I don’t really care about whether I’m right or not about what I just said because it’s all going to become completely irrelevant when we have therapies that repair the damage of aging. Those therapies are going to make the whole concept of life expectancy…the way it’s calculated today will no longer exist.”

Because therapies will make life expectancies of the future, de Grey argues, so much longer than they are today, today’s estimates will become irrelevant. Like trying to compare Mark McGuire, Sammy Sosa and Barry Bonds to Babe Ruth. After steroids, all bets are off.

But that’s not stopping researchers from looking for the “longevity gene.” Sampling the genetic material of centenarians, researchers have seen strong correlations with several genes and the likelihood of living to 100. Two of them are involved in fat metabolism, a third in calcium metabolism.

Despite de Grey’s skepticism, if there really is a genetically-programmed limit around 114, seems to me that would make it all the more imperative to make good on the Longevity Dividend, the range of benefits to both individuals and society were we to stay healthier longer. Some argue that extending life will only postpone the inevitable disease and frailty that comes with old age. But if there were an upper bound that is not affected by current longevity trends, then the longest lifespans will not get longer but the period of age-related disease and frailty would be shortened.

Just my two cents for what they’re worth. Regardless of whether or not the upper bound is real, I agree with de Grey. Biologically, it is a fascinating phenomenon.

[image credits: dailygalaxy.com via Urban Times, Journal of Epidemiology & Community Health, and Archives of Gerentology & Geriatrics]

image 1: old age

image 2: longevity

image 3: rectangularization