Can a Simple Quiz Tell You How Long You'll Live?

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The apocryphal fountain of youth may not exist, but there are ways we can learn to live longer and better lives. On the web, online life expectancy calculators can give users tips on healthier living that could help them tack on a few more years.

"[Life expectancy calculators are] just a repackaged way of telling you what you already know, and that is, 'Eat less, don't smoke,'" says S. Jay Olshansky, a professor in the school of public health at University of Illinois at Chicago. "But what they're really meant to do is encourage people to lead healthier lifestyles, and that's a good thing."

Most of the free online calculators ask users to answer a number of questions related to their family histories, their own medical histories and various behaviors including what they eat, how they drive and how much they sleep. The decidedly ominous Death Clock calculator generates a countdown timer with the number of seconds the user has left to live, but other sites display an age someone with characteristics like the user can expect to attain.

Men in the U.S. have the average life expectancy at birth of about 75 years; females can expect to live about five years longer. Like gender, the most important factors in determining longevity are out of your control: online calculators ask what how long your parents and grandparents lived as a way of assessing your family's medical history. "In order to live a long life, you have to begin by having won the genetic lottery," Olshansky says. "Then you have to avoid getting hit by a bus."

Of course, lifestyle decisions and your own medical history are important. Smoking can knock 10 to 15 years off of an otherwise healthy person's life, and diabetes, obesity, blood pressure, heart disease and cholesterol all factor prominently into formulas life insurance companies use to estimate applicants' life expectancies and set rates for policies, says Paul Graham, VP and chief actuary at the American Council of Life Insurers, an industry trade association.

World events can also play a role; avian flu, if it begins to spread from human to human on a large scale, instead of from bird to human, could cause upwards of 1 million deaths according to some estimates — and that's getting the attention of life insurance companies, Graham says. "That's the biggest event we're watching, much more than terrorism or war."

The key is to remember that the formulas used by both life insurers and online calculators are statistical. The most they can do is predict how long the average person with characteristics similar to yours will live — they can't address you directly. For a life insurance company — which makes or loses money based on large numbers of policy holders living or dying later or earlier than expected — these averages matter. "I need to know that on average, you're going to die at 82," Graham says. "That average doesn't mean anything to you. I don't know that I would make any life-changing decisions based on that."

But online calculators can be useful if they provide suggestions on how to lead a healthier life, Olshansky says. He recommended the Living to 100 life expectancy site, which provides detailed information on changes you can make — everything from what foods to eat to how much you should sleep — based upon your answers to a series of questions. The tools also can help teach the public how to weigh risk factors, said University of Pennsylvania Prof. Dean Foster, co-author of another calculator. "How good is excercise or how bad is smoking?" Foster asks. "Would you walk a mile for a Camel? Each and every Camel? If you do so, smoking is OK. But if you only walk a half mile for each cigarette, it is hazardous to your health."