Here's what it actually means to die 'of old age'

BI Answers: What does it mean to die of old age?

Ever ask someone how their family member passed away and hear them say they simply "died of old age"?

As it turns out, that's almost never quite what's going on from a medical perspective. Aging - in and of itself - is not a cause of death. (There is a phenomenon known as "geriatric failure to thrive," which scientists are studying, but it's extremely rare).

When most of us say someone died of old age, what we really mean is that someone died as a result of an illness (like pneumonia) or an event (like a heart attack) that a healthy, stronger person would likely have survived.

These are often "quiet" deaths - like the kind that happen when an older person's "heart just stopped in her sleep," meaning she likely had a heart attack in the middle of the night, or when someone "had a bad fall, and it was just downhill from there," meaning he or she may have broken a hip and survived surgery but got pneumonia in the hospital and died from the infection.

Most often, what claims the lives of older people is really an accumulation of a whole bunch of things. "As you get older and older, you're more likely to get heart disease and cancer," Amy Ehrlich, a professor of clinical medicine at the Albert Einstein College of Medicine and a geriatric physician at Montefiore Medical Center, told Business Insider. "But we also see a lot of things like falls, where someone falls and ends up with serious trauma like a hip fracture. That's hard to recover from when you're 104."

Which presents us with a question: If we don't die as a result of aging, then what the heck is aging, anyway?

Humans didn't always live long enough to age. We used to die long before our skin began to sag or our muscles began to wither, succumbing instead to diseases for which we now have vaccines, like tuberculosis and the smallpox, and from gastrointestinal infections, which can cause diarrhea.

Somewhere around the 1950s (at least in America and other wealthy countries), we started living nearly twice as long as our ancestors did just a century before. We now spend a massive portion (nearly half!) of our lives getting old. And after that, as the familiar story goes, we die.

But what if it didn't have to be like this? What if we experienced aging, and then came out of it - or didn't age at all?

That's how some animals do it.

A 2014 study comparing the mortality rates of 46 different species, for example, found that some organisms don't age - their mortality rates stay constant from around the time they're born until around the time they die. Others enter a period of aging (like the kind most of us experience around age 65) and then come out of it, continuing on with their lives.

Here's a chart from that study showing what aging looks like in a modern-day human (mortality rates are in red; fertility rates are in blue):

See that sharp rise in the thin red line? We have an astronomically long aging period.

But lots of other creatures' life spans look nothing like this. Take a look at the "immortal" hydra, for example (second column, second row), a tiny freshwater animal that lives to be 1,400 years old. It's just as likely to die at age 10 as it is at age 1,000:

Or check out the desert tortoise, which has a high rate of mortality in early life, but whose rates of mortality decline as it ages, meaning if you're one of these critters who's lucky enough to survive your early years, you carry out your remaining (healthy) days until you reach the end:

So what does all of this mean? Can we stop aging, or at least extend life?

Some scientists think maybe we can.

"Aging is not a relentless process that leads to death," Michael Rose, an evolutionary biologist at the University of California, Irvine and the director of its Network for Experimental Research on Evolution told Business Insider. (Rose didn't work on the study above, but has published a series of papers and books on aging and evolution.) "It's a transitional phase of life between being amazingly healthy and stabilizing."

Other researchers, like biologist and theoretician Aubrey de Grey, want to use our knowledge of these organisms to extend our lives.

The proportion of people who die of age-related problems is high in wealthy countries, says de Grey in his recent film, "The Immortalists." "It's absolutely clear that it's the world's most important problem."

But for now, we are not hydra (or tortoises), and we can't do away with aging.

For us, aging is real and it is long. Fortunately, many older people can still live healthy, happy lives.

"If someone's 104, there's not a whole lot you can do," says Ehrlich. "But someone who's 83? There's plenty you can still do."

This post is part of a continuing series that answers all of your questions related to science. Have your own question? Email science@businessinsider.com with the subject line "Q&A"; tweet your question to @BI_Science; or post to our Facebook page.

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