The field of longevity research is running high on optimism these days. “Life expectancy is lengthening almost linearly in most developed countries, with no sign of deceleration,” say the authors of the recent Lancet article “Ageing Populations: the challenges ahead.”  They add, “Continued progress in the longest-living populations suggests that we are not close to a limit" for age.

Life expectancy is increasing in all developed countries; reaching 82.1 years in Japan, 81 years in France and 78.1 in the U.S. In total, during the twentieth century, life expectancy increased by a remarkable 30 years or more in Western Europe, the USA, Canada, Australia, and Japan. And there is no sign that this trend is slowing.

Last week, Time magazine’s cover story, “The Science of Living Longer,” featured a look at some of the “oldest, old;” the fastest growing portion of our aging population. These are the folks that are living into their 90’s and, for nearly 100,000 Americans, even past the century mark. Of particular interest to researchers is the growing group of enduring souls who, despite advanced age, are not sickly, frail and bedridden. Instead these modern-day Methuselahs are remarkably resilient; bouncing back from illness and injury without becoming seriously disabled. By focusing on this group, scientists are hoping to identify which genetic, lifestyle and environmental factors are most important for not only extending longevity, but also avoiding the burdens of disabilty.

The quest for immortality—or at least a very ripe old age—predates even the elusive hunt for the “fountain of youth.” Looking younger, feeling younger and living well beyond our golden years has ultimately become the underlying goal of modern medicine. In the earlier part of the twentieth century, life expectancy increases were mainly due to improvements in infant and childhood survival and the successful treatment of infectious disease.  But since 1950, most of the gains have been achieved by keeping older Americans alive longer through prevention (quitting smoking, diet, and exercise) and better diagnosis and treatment of heart disease, cancer and other chronic ills. Yet in the clinical setting, this pursuit of longevity has been most focused on the last two years of patients' lives; driven by advances in technology that dramatically drive up health care expenses—too often extending life without really improving its quality.

What factors will extend longevity into the next century? Genetics contribute about 30% to our life-expectancy, but it turns out that lifestyle choice, environmental factors and luck (whether or not we get hit by a bus, for example) contributes the rest. Maintaining the current trend in life extension will require more advances in treating chronic ills, as well as continued success in reducing smoking rates and addressing the growing obesity epidemic. If a new drug comes along that prevents telomere shortening (a biological cause of cellular ageing), or reduces cellular oxidation or mimics the protective effects of red wine, then longevity and healthy old age will perhaps be extended more quickly and more dramatically—at least among those that can afford the treatment.

By all indications, the next several decades will see a dramatic shift toward an aging America. The most recent Census projection is that the number of people age 65 and over will increase to 88.5 million in 2050, more than doubling the number in 2008. Similarly, the 85 and older population is expected to more than triple, from 5.4 million to 19 million between 2008 and 2050. The Lancet article predicts that children born in this decade have at least a one in two chance of living to be 100.

Despite the optimistic nature of these projections, we really don’t know how many of these people will be truly living—not just kept alive. And that’s where the issue gets complicated. Although life-expectancy is increasing, so is the incidence of multiple medical problems and chronic disease in the elderly. Cardiovascular disease, diabetes, lung problems, arthritis, depression and pain all appear to be increasing in the elderly population; some 38% of the elderly covered by Medicare have multiple chronic conditions, according to Health Affairs.

What this tells us is that doctors have made progress in earlier diagnosis of chronic disease and in treatment; postponing disability until later ages. But for people living beyond 85, the picture is decidedly less rosy. Most studies seem to show that disability increases with advanced age and that “survival to the highest ages is associated with worse health,” according to the Lancet article.

In terms of health care costs, progress in extending life presents a significant problem. All of these extra old people will be covered under Medicare. And although “limitations and disabilities” may be postponed in some of these nonogenarians and centenarions, treating all that chronic disease will still add up to a huge increase in doctor visits, expensive medications, therapy, and diagnostic testing. Even healthier old people need knee replacements, hip replacements, heart valves, hearing aids and other surgeries and treatments to keep them active. It doesn’t really matter if older people become less disabled in the future; they will still use more medical goods and services than younger adults. The average health care spending for Americans over 65 was $8,800/year in 2006; for those ages 45-64 that figure drops to $4,900.

Besides increased health care costs, an aging population puts other strains on society. The Time article describes many of them:  if they retire at 65 they spend more years living on pensions, Social Security and Medicare; if they continue to work they take jobs from younger people. They would add to the loads of trash, produce more greenhouse gases and tax the dwindling water supply. And finally, we will need special housing and personnel to take care of the oldest, old as they inevitably will one day become disabled and frail.

These, of course, are issues that require a national strategy that includes tackling serious Medicare reform. But we also face a more personal, moral challenge as life expectancy continues its relentless march forward: We must begin to separate preventative strategies and new treatments that will help older people age better—avoiding long-term disability, dementia and frailty—from those that merely extend life at any cost. We can only do this by having honest conversations about end-of-life issues; in medical schools, among families and between doctors and patients.  In his piece “The Case for Killing Granny,” in Newsweek, Evan Thomas writes:“[T]he need to spend less money on the elderly at the end of life is the elephant in the room in the health-reform debate. Everyone sees it but no one wants to talk about it.” (Probably because when legislators do support the idea of such conversations Conservatives accuse them of advocating death panels.)

The figures speak for themselves: Almost a third of the money spent by Medicare—some $66.8 billion each year—is spent on chronically ill patients in the last two years of life. A remarkable $50 billion of that is spent on hospital and doctor bills just for the last two months of these patients’ lives. The Urban Institute, a nonpartisan research center, found that the government could save $90.8 billion over 10 years by better managing end-of-life care.

“Until Americans learn to contemplate death as more than a scientific challenge to be overcome, our health-care system will remain unfixable,” says Thomas.