Life Expectancy: Facts and Predictions
The reality is that life expectancy has been steadily increasing in the last 160 years by about 3 months per year. Where will this trend lead us? Is there an upper limit?
Predictions of life expectancy have great socioeconomical implications. Insurance companies and health and social security agencies base their policies on such predictions. An increase in life expectancy of a few years can produce large changes in the overall numbers of the old and very old. Analysis of the factors that may have an influence on life expectancy is, therefore, of great importance. Plotting life expectancy vs time, starting in 1840, we obtain a straight line that does not seem to approach a maximum nor reach a plateau. Reason, however, tells us that there must be a limit, and this has always been the view of the experts in the field, who envision various biological barriers and practical impediments to the steady rise in life expectancy that we have seen so far.
Predictions of life expectancy were the topic of Jay Olshansky's presentation, from the University of Illinois, Chicago, who stated his conclusions first and then presented the facts that had led him to it. His conclusion: There is sufficient evidence to predict that in developed countries life expectancy will decline in the first 50 years of the 21st century.
Why do we live as long as we do? The increase in life expectancy seen in the last century occurred predominantly because we succeeded in saving young people who would have otherwise died. In the 21st century, we can produce a similar increase only by increasing the life expectancy of the old. But so far, the epidemiologic data seem to argue against this possibility. Since 1981, life expectancy at 65 years has remained constant at 19 years, after a steep rise in the 1930s.
There are several constraints to the duration of life: biochemical, biological, demographic, and stochastic. According to Olshansky, 2 factors that will have a great influence on life expectancy in the next decades are infectious diseases and obesity. Unless suitable interventions are implemented, countries with high incidence and prevalence rates of either factor are not expected to fare well in terms of overall life expectancies. The percentage of the US population that can be defined as obese has risen from 10% in the 1960s to about 30% today. The phenomenon is particularly worrying in children, especially those belonging to minorities. Today 25% of Hispanic children in the United States are obese vs 10% in the 1960s. In other countries, the rate of obesity is also increasing, although the absolute percentage is lower: 3% in Japan, 7% in Switzerland, 9% in Italy, 10% in France, and 13% in Spain.
With regard to infectious diseases, there are several factors from which Olshansky predicts that they will become an increasing concern: the increase in antibiotic-resistant organisms, the more rapid and efficient transport across the world (eg, SARS), and the increase in the population of immunocompromised subjects (eg, due to aging, HIV, and chemotherapy). The overall mortality by infectious diseases in the United States has risen by 39% since the beginning of the 1980s (with a 4.5% increase per year between 1980 and 1995) -- by 25% in the population older than 65 years and by 6-fold in the population aged 25-44. Hospital-acquired infections are increasingly resistant to treatment. In addition, although about 20,000 influenza-related deaths have been observed in the United States between 1969 and 1996, they have increased to about 70,000 since 1996.
In conclusion, Olshansky is of the opinion that although advances in biomedical technology and modifications in lifestyle will allow life expectancy to continue its slow rise in the short term, a repetition of the large and rapid gains in life expectancy observed during the 20th century are unlikely, because this would require the ability of slowing the rate of aging -- something that we don't seem to be able to do today.
According to the novelist Alessandro Manzoni, "Ai posteri l'ardua sentenza" -- only posterity will know whether these predictions turn out to be true.
© 2004 Medscape
Cite this: Caloric Restriction and Life Expectancy - Medscape - Dec 23, 2004.