The dramatic increase in average life expectancy during the 20th century ranks as one of society’s greatest achievements. Although most babies born in 1900 did not live past age 50, life expectancy at birth now exceeds 83 years in Japan—the current leader—and is at least 81 years in several other countries. Less developed regions of the world have experienced a steady increase in life expectancy since World War II, although not all regions have shared in these improvements. (See female life expectancy chart below.)
The progressive increase in survival in the oldest age groups was not anticipated by demographers, and it raises questions about how high the average life expectancy can realistically rise and about the potential length of the human lifespan. While some experts assume that life expectancy must be approaching an upper limit, data on life expectancies between 1840 and 2007 show a steady increase averaging about three months of life per year. The country with the highest average life expectancy has varied over time. In 1840 it was Sweden and today it is Japan—but the pattern is strikingly similar. So far there is little evidence that life expectancy has stopped rising even in Japan.
So can we extend life expectancy even further? Recent experiments on everything from roundworms to mice are giving some scientists hope that our maximum life spans are not set in stone but can be extended far beyond what nature intended.
The first hint of the possibilities came in the 1930’s, when studies by Cornell University researchers discovered that rats fed severely reduced calories tended to live up to 40 percent longer than their fully fed litter mates. Recent studies with rhesus monkeys seems to confirm that work.
Scientists still aren’t sure how caloric restriction, or CR, works. One early hypothesis, that CR regimens extended life span by preventing animals from reaching full body size, was debunked when experiments showed that even fully grown adults can benefit from CR. For about 50 years, CR was the only proven method to extend an organism’s maximum life span in a healthy way.
Then in 1996, scientists discovered a type of mutant dwarf mouse that lived up to 70 percent longer than its non-mutated peers. The rodents’ stunted growth was due to a change at the genetic level that reduced production of hormones related to growth.
In the years since, genetic experiments have also produced more enduring yeasts, roundworms and fruit flies. Much of the anti-aging research is still done on rodents, whose biological systems are similar to humans in many ways. In fact, a leading proponent of human anti-aging research has organized a hefty prize for breakthroughs that extend the lives of mice.
Scientists have also discovered other factors that affect life span in research that might eventually be applied to humans. A study out of Cambridge University in England found that what a mother eats during pregnancy and while nursing can greatly affect her children’s life spans.
Using mice, the researchers found that mothers fed protein-rich diets during pregnancy, but low-protein diets while breast-feeding, had pups that lived up to 50 percent longer than those for whom this feeding pattern was reversed. If a similar approach could work for humans, this translates into a difference between reaching 50 and living to be 75 years old, the researchers said.
Fall in Love, Get Married, and Stay in Love
If the thought of eating only enough to survive or having your genes toyed with doesn’t sound very appealing, scientists say there is another and perhaps more pleasurable way to live longer: fall in love.
A recent study led by Linda Waite, a sociologist at the University of Chicago, showed that happily married couples tend to live longer than unwed individuals. Married men were found to live, on average, 10 years longer than non-married men, and married women lived about four years longer than non-married woman.
The researchers speculated that married men live longer because they adopt healthier lifestyles and take fewer risks. Married woman, on the other hand, probably live longer because of the improved financial well-being that comes with marriage.
How Far Can We Go?
There are conflicting opinions among scientists about the degree to which human life expectancy can be extended from its present level. Nir Barzilai, director of the Institute for Aging Research at the Albert Einstein College of Medicine, is one of the pessimists. “Based on the biology that we know today, somewhere between 100 and 120 there is a roof in play and I challenge if we can get beyond it.” Craig Venter, a pioneer in human genomics, is one of the optimists. “I don’t see any absolute biological limit on human age,” he says, arguing that cellular immortality–in effect running the clock backwards–should be possible. “We can expect biological processes to eventually get rid of years.”
One thing is certain: our desire for longer, healthier lives will not likely diminish.