A rise in life expectancy to 100 years in the United States in this century would profoundly influence many aspects of society,41 including the solvency of age-based entitlement programs and tax rates levied by the federal government. Even marginal increases in life expectancy beyond those anticipated by the SSA would markedly increase the number of octogenarians, nonagenarians, and centenarians that the SSA expects. However, in light of the obesity-driven trends in the health status of the U.S. population (especially the young), the bases for the SSA's recent decision to raise its midrange forecasts of life expectancy beyond the increases anticipated during the next 70 years merit reconsideration.

Figure 2. Figure 2. Observed and Projected Life Expectancy at Age 65 for U.S. Females (1900 to 2000). Shown are observed changes, from 1900 to 1980,42 in expected remaining years of life at age 65 for females in the United States, and projections of the expected remaining years of life at age 65 made by the SSA in actuarial studies published in 1952,43 1966,44 and 1974.45

Figure 3. Figure 3. Observed and Projected Life Expectancy at Age 65 for U.S. Females (1980 to 2050). Shown are observed changes, from 1980 to 2000,46 in expected remaining years of life at age 65 for females in the United States, projections of the expected remaining years of life at age 65 made by the SSA in actuarial studies published in 198146 and 1984,47 and forecasts based on the SSA's 1995 and 2003 Trustees Reports.48,49 A forecast of the expected remaining years of life at age 65 for females in the United States, assuming the observed trend from 1940 to 2000 is extrapolated linearly from 2000 to 2050, is shown.

Figure 2 shows the historical trend in life expectancy at age 65 for females in the United States from 1900 through the inception of the Social Security program, in 1935, and formal projections of the rise in life expectancy at age 65 made by the SSA at various times since then. Before 1980, the SSA consistently underestimated the subsequent rise in life expectancy at age 65 because it assumed that recently observed gains could not be sustained. After 1980, this position was reversed, and the SSA began tracking and extrapolating more recently observed trends in life expectancy at age 65. Ironically, this change in approach occurred just when the rise in life expectancy began to stall (Figure 3). The fact is, life expectancy at age 65 for females has remained largely unchanged for most of the past 20 years.

A central problem with the SSA's forecast is best illustrated by its projections for diabetes. From 1979 to 1999, rates of death from diabetes increased annually by an average of 2.8 percent for males and 1.8 percent for females. In 1990, diabetes decreased life expectancy by 0.22 year for males and 0.31 year for females,40 but the negative effect of diabetes on life expectancy has grown rapidly since then. However, the negative effect of diabetes on the life expectancy of the population could now be several times as great as it was in 1990.31 Given the rapidly rising prevalence of diabetes and the prospect that childhood obesity today will probably accelerate the rising prevalence of diabetes in the coming decades, it is difficult to justify the SSA's assumption that rates of death from diabetes will decline by 1.0 percent to 3.2 percent annually throughout the 21st century, beginning in the year 2010.5

We anticipate that as a result of the substantial rise in the prevalence of obesity and its life-shortening complications such as diabetes, life expectancy at birth and at older ages could level off or even decline within the first half of this century. This is in contrast to both the recent decision by the SSA to raise its forecast of life expectancy and what we consider to be the simple but unrealistic extrapolation of past trends in life expectancy into the future.

There are other realistic threats to increases in life expectancy. From 1980 to 1992 in the United States, the age-adjusted rate of death from infectious diseases rose by 39 percent, an increase fueled mostly by the AIDS epidemic; the overall rate of death from infectious diseases increased 4.8 percent per year from 1980 to 199550; hospital-acquired infections have increased51,52; hospital-acquired and antibiotic-resistant pathogens have entered the community and our food supply53,54; and recent decreases in mortality related to the human immunodeficiency virus have leveled off.55

Infectious diseases could decrease life expectancy substantially if pandemic influenza strikes.56 Developing and developed nations are far more vulnerable to a global pandemic of influenza today than in 1918, owing to an aging population, resistance to antibiotics, and more rapid transport of microbes, among other reasons. This heightened risk is balanced in part by better global surveillance and interventions already present.57 Although estimating the negative effects of epidemics on the future course of life expectancy is problematic, it has been established that infectious diseases, when they do emerge, can wipe out a century's worth of gains in health and longevity in less than one generation.58 Other forces that could attenuate the rise in life expectancy include pollution, lack of regular exercise, ineffective blood-pressure screening, tobacco use, and stress.

Advances in the medical treatment of major fatal diseases, including the complications of obesity, are likely to continue. Unfortunately, recent trends in the prevalence of cancer and in the rates of death from cardiovascular diseases in the United States reveal only marginal gains in longevity in recent decades,59,60 and even the gains produced from the elimination of any one of today's major fatal diseases61 would not exceed the negative effects of obesity that appear to be forthcoming.

A leveling off or decline in life expectancy in the United States is not inevitable. We remain hopeful that the public health community and public policymakers will respond to the impending dangers that obesity poses to both the quality and the length of life. However, the negative effect on health and longevity of unchecked obesity is substantial according to statistics on health and mortality that can be observed for the generations currently alive, as has already been shown in Okinawa, Japan.62 It is important to emphasize that our conclusions about the future are based on our collective judgment, as are all forecasts, and we acknowledge that forces that influence human mortality can change rapidly.

Finally, our forecast has other public-policy implications. Dire predictions about the impending bankruptcy of Social Security based on the SSA's projections of large increases in survival past 65 years of age appear to be premature. However, this “benefit” will occur at the expense of the economy in the form of lost productivity before citizens reach retirement and large increases in Medicare costs associated with obesity and its complications.63 Presently, annual health care costs attributable to obesity are conservatively estimated at $70 billion to $100 billion.64,65 With rapid increases in the prevalence of diabetes, and a decrease in mean age at the onset of diabetes, the cost of treating diabetes-related complications, such as heart disease, stroke, limb amputation, renal failure, and blindness, will increase substantially. A similar escalation of health care costs from other complications associated with obesity (e.g., cardiovascular disease, hypertension, asthma, cancer, and gastrointestinal problems) is inevitable. The U.S. population may be inadvertently saving Social Security by becoming more obese, but the price to be paid by obese people themselves and the economy is already high enough to justify considerably increased spending on public health interventions66 aimed at reducing the incidence and severity of obesity.

Unless effective population-level interventions to reduce obesity are developed, the steady rise in life expectancy observed in the modern era may soon come to an end and the youth of today may, on average, live less healthy and possibly even shorter lives than their parents. The health and life expectancy of minority populations may be hit hardest by obesity, because within these subgroups, access to health care is limited and childhood and adult obesity has increased the fastest.67 In fact, if the negative effect of obesity on life expectancy continues to worsen, and current trends in prevalence suggest it will, then gains in health and longevity that have taken decades to achieve may be quickly reversed. The optimism of scientists and of policymaking bodies about the future course of life expectancy should be tempered by a realistic acknowledgment that major threats to the health and longevity of younger generations today are already visible.