»How Long Can Our Lives Be Extended?«
The gerontologist Karl Lenhard Rudolph talks about the consequences of evolution
What happens to people when they age? Why do we get old and die? Over the millions of years of evolution, most living organisms have been programmed to reach the pinnacle of their capabilities at the ages when they reproduce. Such organisms can be regarded as having completed their mission after they have reproduced and the next generation has reached maturity. The same is true of human beings. Our hard drive, by which I mean our genes and the way they are connected with one another, achieves optimal fitness between the ages of 25 and 40. Evolution doesn’t concern itself with what happens after that (except for the low evolutionary utility of the grandparents helping to bring up the grandchildren). So aging begins after the reproductive years have passed. The nerve cells in the brain begin to lose their plasticity and stop forming synapses, stem cells stop dividing, and the ability of organs to regenerate themselves decreases. Simultaneously, the number of mutations and defects increases. In the meantime, proteins clump together and toxic substances lead to chronic inflammation in nearly all body tissues. Aging begins when this loss of cell and organ functioning sets in.
»There’s a biological limit to life expectancy—100 years, or 120 at the most«
What happens to mental capabilities?
Mental development also follows this pattern, but not as clearly. The aging individual experiences a loss of creativity, but he or she also gains experience. There are some artists who didn’t write their greatest works or compose their best music until they were relatively old. In general, it’s true here as well that as people age, their ability to learn new things diminishes and their memory deteriorates.
Still, people keep living longer. At the beginning of April, an Italian woman named Emma Morano died at the age of 117. What are the limits of longevity?
I believe there’s a biological limit to life expectancy that I would say could be 100 years, or 120 at the most. We shouldn’t be fooled by the fact that the average life expectancy in Germany has doubled in the last 200 years from the mid-40s to the mid-80s and will likely increase to 90 by 2035. This increase is mostly due to illnesses being detected at an earlier stage of their development, improved treatments, and the fact that people live healthier lives. They have a better diet and enjoy better living and working conditions. All of this slows aging processes, but it doesn’t stop aging as such. The ageing process, which is launched by evolution to reduce the ability of all of our systems to function properly after our reproductive years are over, cannot be shut down that easily.
There are regions in which people live longer (see our report on page 46). Why is that? Can we learn anything from the people in those regions?
Good diets and lifestyles definitely play a role in healthy aging. The olive oil often used in Mediterranean countries and the consumption of fish in Japan can have a positive effect on life expectancy. We also know that stress and obesity accelerate biological aging, while sports and exercise have a positive effect. It’s important to understand that although we can’t do much about our genetic makeup, we can change our habits in order to live healthier lives.
Some say that those who go hungry live longer. Is that true?
Lower food intake lengthens the lifespan and improves the health of various organisms. This was first demonstrated with flies and worms, but these days we also know it to be true about mice and monkeys. It’s not just the metabolism decrease that slows the aging process here, as a large number of protective mechanisms— such as autophagy—are also triggered when caloric intake declines. Autophagy launches a process in which cells detect damaged proteins and disassemble them. This type of detoxification has a positive effect. However, lower food intake also inhibits the formation of immune cells. That increases an organism’s susceptibility to infection.
Japanese stem cell researcher Shinya Yamanaka has demonstrated in the laboratory that it is possible to reset the life clock of every cell in the body back to zero—the embryonic stage. In 2012 Yamanaka was awarded the Nobel Prize in Medicine for this reprogramming feat. Doesn’t his research point the way toward defeating the aging process?
Research conducted on mice has shown that it is in fact possible to rejuvenate tissue with cell reprogramming. The danger here is that you might end up not only reprogramming the cells you want to affect but also activating other cells that never come to rest—and can therefore turn cancerous.