Americans may be less optimistic about the future in general than they once were, but a solid majority still hopes to enjoy a long life. In fact, longevity is considered by most as part of a good life, on par with health, prosperity and loving relationships.

60 percent expect to live at least until they’re 80. 40 percent think 120 to 150 years could be feasible within their own lifetime due to further advancements in medical and biological technology. And one percent believes that death could eventually be eliminated altogether, according to a survey conducted by David Ewing Duncan, a science writer and author of “When I’m 164: The New Science of Radical Life Extension and What Happens If It Succeeds.”

Considering that two thirds of the population are currently dealing with weight problems and a host of lifestyle-related diseases, this may be wishful thinking for many. But the fact is that the average life expectancy has indeed dramatically increased over the last century due to improved hygiene, diet and medical care. In 1900, people could expect to live just under 50 years. In the year 2000, it was nearly 77. The average lifespan was lengthened between 1.5 and 2.7 years per decade, according to data collected by the U.S. Census Bureau.

What’s even more stunning is that our chances of living longer seem to go up all the time. How so? “Because the more time you spend in the world, the more time the world gives you,” says Ted C. Fishman, author of “Shock of Gray” (Scribner, 2010). “For every hour we live,” he claims, “the average human lifespan increases between eleven and fifteen minutes. Every day sees the average lifespan grow another five hours.”

Of course, that doesn’t apply for everyone across the globe, Fishman admits. “Your odds are better if you have avoided the obesity epidemic and live in a place that enjoys good health care, education, and freedom from war and terrible poverty.” It also helps if you can manage to stay mentally fit and don’t suffer from memory loss and cognitive decline. A loving family, a circle of friends and other supportive social surroundings add to your chances.

Unfortunately, many of these important factors for longevity cannot be taken for granted. Baby boomers, now entering retirement, are rightly worried about their prospects when it comes to their financial security, health needs and social life.

“It does not bode well for the baby boom generation at all,” warns Dr. S. Jay Olshansky, a professor for public health at the University of Illinois at Chicago who studies longevity, in an interview with Reuters. More recent studies show that life expectancy gains in the U.S. have actually flattened out since the 1960s. Despite of dramatically increasing expenditures for health care, many Americans live with chronic diseases that are left insufficiently treated, especially among the uninsured and those with limited coverage. One study concluded that poorer citizens have on average a shorter lifespan of up to five years than the more affluent.

Obviously, money can’t buy everything and life remains an uncertain enterprise no matter how rich you are. For the rest of us, there are plenty of opportunities to take care of our health and well-being by eating right, exercising, etc. (you know the drill) – and for this, it’s never too early to get started.

Researchers found that physical fitness achieved during middle-age can lower the risk of developing chronic diseases like diabetes, heart disease, high blood pressure in later years and may be associated with compression of morbidity at old age. Compression of morbidity is what many health experts consider the optimal outcome of aging. The idea is “to delay the onset of age-related disease and inevitable decline without worrying about extending life,” writes Dr. Andrew Weil, author of numerous best-selling health books, including “Healthy Aging” (Knopf, 2005). Not longevity itself should be our first concern, but the quality of life we have as long as we are around, he says.

This reminds me of the late Steve Jobs, the founder of Apple Inc. who died last year at the age of 56, when he spoke of the inevitability of death at his 2005 Stanford Commencement Address.

“No one wants to die,” he said. “Even people who want to go to heaven don’t want to die to get there. And yet death is the destination we all share. No one ever escaped it. And that is as it should be because Death is very likely the single best invention of Life. It is Life’s change agent. […] Your time is limited,” he ended, “so don’t waste it…”

Even the longest life can be a waste if it’s not brought to its full potential. Even the shortest life is rich and fulfilled if it’s lived well.

If you enjoyed this article, you may also be interested in “The High Cost of Living Longer.”

Timi Gustafson R.D. is a clinical dietitian and author of the book “The Healthy Diner – How to Eat Right and Still Have Fun”®, which is available on her blog, “Food and Health with Timi Gustafson R.D.” (http://www.timigustafson.com), and at amazon.com. You can follow Timi on Twitter and on Facebook.