How long can humans live for? Dr. Rhonda Patrick here, and today we're going to talk about longevity. But today, instead of talking about average life expectancy, we're going to talk about maximum lifespan. Since the turn of the 20th century, maximum recorded age at death has risen from 110 to 122, a record held by Jeanne Calment of France, which still no one has surpassed since her death in 1997. But theoretically, what is the longest a human could live? Or is there even a limit at all? This question still sparks debate, with most falling into 3 camps. First, that there's a fixed limit to human aging, an age that can never be surpassed regardless of improvements in medicine and technology. Second, that there's an increasing but hard limit.

In other words, an age that cannot be surpassed by someone today, but we could find ways to push higher with medicine and technology in the future. And lastly, that our lives are theoretically unlimited. If that were the case, then given enough time and people, we'd see increasingly older and older ages reached with no ceiling, even if it can still be extremely unlikely that people will reach a certain age. That's a potentially exciting idea. So what is the chance that we'll start to see more supercentenarians, those who reach age 110? Or even someone exceeding Calment's record anytime soon. While these 3 ideas are still debated and there are studies showing evidence for each, let's take a look at a pair of recent studies that support the 3rd one.

The first study of this pair found that astonishingly, your chance of living for another year at age 110 is the same as at age 120. Let's take a look at how researchers use some clever math to figure this out. There's a big challenge when studying extreme old age, a very small data pool. For example, what are the odds someone makes it from age 110 to 111? There's not a lot of data, which means there's a lot of uncertainty. Going a step further, what if we want to determine the odds of something happening that's never happened before, like a person reaching the age of 130? In other words, we're interested in the very tail end of the survival curve, age 110 and beyond, the supercentenarian zone.

Does the curve keep approaching 0 without ever hitting it, which would imply a theoretically unlimited lifespan? Or does it eventually hit 0, indicating a hard limit? Since we don't have enough data to answer that question definitively, we have to use statistics to model the tail end. Specifically, something called extreme value theory. Extreme value theory is a branch of statistics used to study incredibly rare events, and it works by fitting a specific type of probability distribution to data points over a certain threshold. Take, for example, a 1,000-year flood, a flood so big it only occurs every 1,000 years on average. Let's say you were trying to engineer a bridge to survive one of these freak flooding events.

So you look back over your 300 years of water level data, but come up against a problem. That data is very unlikely to contain anything as large as a 1,000-year flood. You'd need about 4,000 years of data to have a 98% chance that it contains a 1,000-year flood. That's where extreme value theory comes into play. It helps engineers and scientists estimate the probability of events more extreme than any we've previously observed. Floods, earthquakes, traffic jams, market crashes, and of course, aging. In this case, it's applied to a number called the force of mortality. While the more commonly used age-specific probability of death describes the chance you'll die over a period of time, force of mortality uses calculus to describe someone's susceptibility to dying at any given moment.

This is important because when studying extreme old age, We don't just want to know how the risk of dying changes each year, but also over the course of each year. Force of mortality is much more granular. Its value isn't really what's important for this study. Rather, the key is how it's changing. As adults age, we generally see the force of mortality and probability of death slowly increasing. If human lifespan was limited, we'd expect to see the force of mortality rise higher and higher, approaching infinity at the age limit, which would look something like this. But what researchers found was that instead, the force of mortality flattens out after age 110, looking like this. And that flat graph is the big finding here.

While the force of mortality does increase in old age, this analysis finds that by age 110, Your chance of surviving another year levels off at around 47%, like flipping a coin every year. In other words, there doesn't seem to be an upper limit to how old someone could live, but the chances of your coin flip coming up heads every time start to get pretty slim before long. And interestingly, researchers didn't see any statistically significant differences between sex, genetic background, diet, or other lifestyle factors for 110 to 115-year-olds either. But there's a big caveat to this. Remember, the sample size, unsurprisingly, is very small. There were only 566 lifespans used for the model, and only 9 of those reached their 115th birthdays.

So we're making predictions about ages that very few people have ever lived to. OK, so that answers one big question. But what about the likelihood that we'll see people surpass age 120 or even higher ages in the next century. The second study I want to talk about builds off the last one by running a forecast using the unlimited but short model and taking population projections into account. Researchers projected forward to the year 2100 and found that the current maximum age record still held by Jeanne Calment will almost certainly be broken by the end of this century. However, it seems unlikely that anyone will live beyond age 135 in that time. Over the next few decades, we should start to see whether this model continues to hold up as more data comes in.

If the model is accurate, we'll begin to see more validated supercentenarians that fit the model. However, this is just one model, and there are many others out there that show different results. While the research into maximum lifespan is fascinating from a theory point of view, you're probably more interested in how you yourself can reach a healthy old age. Many scientists are hard at work trying to increase the human lifespan and healthspan, which could also increase the number of people who reach supercentenarian status. To get there, one of the best bets seems to be on finding ways to reduce the burden of chronic inflammation and identify lifestyle factors that improve metabolic health.

Researchers have different ideas of where we should be focusing our efforts, but there are some promising technologies on the horizon that may slow or even reverse some markers of aging. One I'm particularly excited about is interrupted cellular reprogramming. This technology utilizes the Yamanaka factors, 4 transcription factors that play a role during embryonic development. When the Yamanaka factors are added to adult cells, they can reset an adult cell to become a pluripotent stem cell and revert the cell to an embryonic-like state. Interrupted cellular reprogramming, which has been demonstrated in mice, involves transiently pulsing these factors so that rather than reversing to an embryonic state, the cells regenerate and seem to become younger.

To sum up, there's a lot of exciting research right now into aging and maximum lifespan. And one possibility is that our lifespans may in fact be theoretically unlimited, even if practically short. But that said, we've really just scratched the surface of this topic, and other research has suggested that there could be a fixed limit. As time goes on, more data will mean we can continue to refine and improve these and other models. And in the meantime, researchers are continuing to focus on ways to not only reach greater ages, but also reach old age while maintaining health. I'm Dr. Rhonda Patrick, and I'll catch you next time.