Some interesting points are raised in an article I noticed today:
The aging population increase in the US and throughout the developed world appears to correlate with a switch from acute infectious diseases to chronic diseases as the major cause of morbidity and mortality.
Some diseases like ulcers and certain types of cancer, once thought to be primarily related to lifestyle factors, are now known to be caused by microorganisms, and many more syndromes, including some psychiatric conditions, may have a connection to infection.
Scientists propose that much of the (entirely incidental) increase in average and maximum healthy life span over the past century stems from removing the damage done to our bodies by disease over a lifetime. Less disease means less damage - which means a better chance of a longer life according to the reliability theory of aging. This article proposes that medical science has, to date, only managed to deal with the easy half of the disease problem:
Up until the late 20th century, health professionals believed that chronic diseases such as peptic ulcers and cervical cancer were caused in part by lifestyle factors such as diet, stress and exposure to environmental toxins. In the last several decades, researchers have compiled strong evidence that most peptic ulcers are caused by an infection with the bacterium Helicobacter pylori and can be treated with antibiotics. An infection with human papillomavirus (HPV), the cause of genital warts, appears to be the cause of cervical and other cancers.
In addition to H. pylori and HPV, the report lists 30 other microorganisms for which there exists strong evidence of an associated chronic disease. The report also lists over 40 other chronic diseases, including heart disease, Alzheimer's and schizophrenia, which are suspected of having an infectious cause.
Proving causation is difficult. Scientists have traditionally applied a series of tests, known as Koch's postulates, to establish that a specific microorganism does indeed cause the associated disease. Because of the complex nature of chronic illnesses, oftentimes it is not practical or even possible to use Koch's postulates to prove the infectious nature of chronic illness. The report recommends that new criteria for evaluating the strength of association between microbes and chronic illnesses be developed.
The lack of progress to date in more important age-related conditions may be as much a function of the difficulty of identifying a cause as it is a function of these conditions only becoming more prevalent as more people live longer lives.
I point this out as a matter of interest - it is of course still that case that far more progress in healthy life extension can and should be made by directed research into extending the healthy human life span. We do need cures for chronic age-related conditions (infectious agents or not), but a great deal of funding is already invested in that research. Not so for the fight to cure aging, alas.