Even if one does not die while infected the infectious diseases take their toll and accelerate aging in a number of ways.
First off, the pathogens directly do damage to the body.
Second, the immune system’s response does damage. In the process of attacking pathogens the immune response causes collateral damage to human tissue. Chemical compounds released by immune cells do damage to our own cells.
Third, infection reduces our ability to stay nourished due to decreased appetite, diarrhea, decreased ability to do activities that bring in food, and other mechanisms.
Therefore a reduction in infectious disease exposure has reduced the rate at which our bodies accumulate damage.
Gina Kolata of the New York Times has written a great article surveying the building body of evidence which shows earlier generations got classic diseases of old age sooner and did so due to infections while very young and poorer nutrition. (and I strongly urge you to read the full article)
New research from around the world has begun to reveal a picture of humans today that is so different from what it was in the past that scientists say they are startled. Over the past 100 years, says one researcher, Robert W. Fogel of the University of Chicago, humans in the industrialized world have undergone “a form of evolution that is unique not only to humankind, but unique among the 7,000 or so generations of humans who have ever inhabited the earth.”
We humans alive today are physically way different on average as compared to previous generations.
In previous centuries heart disease, lung disease, and other ailments showed up decades earlier in human lives.
The biggest surprise emerging from the new studies is that many chronic ailments like heart disease, lung disease and arthritis are occurring an average of 10 to 25 years later than they used to. There is also less disability among older people today, according to a federal study that directly measures it. And that is not just because medical treatments like cataract surgery keep people functioning. Human bodies are simply not breaking down the way they did before.
What is most interesting about these results are the suspected causes: events in the womb and while still quite young can set people up for chronic diseases decades later.
The proposed reasons are as unexpected as the changes themselves. Improved medical care is only part of the explanation; studies suggest that the effects seem to have been set in motion by events early in life, even in the womb, that show up in middle and old age.
“What happens before the age of 2 has a permanent, lasting effect on your health, and that includes aging,” said Dr. David J. P. Barker, a professor of medicine at Oregon Health and Science University in Portland and a professor of epidemiology at the University of Southampton in England.
But it is too late for us to go back in time and tell our mothers to avoid people with colds and flus and other infectious diseases. Our bodies are damaged even from before birth.
Excellent post from the excellent FuturePundit