In the course of writing entries here and at the Longevity Meme, I comment on a fair amount of medical research that will - hopefully, likely, eventually or maybe - lead to longer, healthier lives for all of us. However, very little of this research is carried out with the intention of achieving this worthy goal. Take the field of regenerative medicine, for example: coupled with a reliable cure for cancer, stem cell based regenerative medicine will greatly extend our healthy life spans. Few - if any - scientists in the field have this goal in mind, however. They are curing Parkinson's, Alzheimer's, osteoporosis or diabetes, or working to create replacement organs to order ... seeking cures for specific (usually age-related) problems, in other words.
Almost all human healthy life extension achieved over the past 150 years or so has been accidental, incidental, or otherwise unrelated to the motivating goals of medical research. It just so happens that if you cure and prevent enough cumulative damage to the body - disease and chronic conditions - average live spans get longer. Nothing mystical going on here.
"Infectious diseases cause chronic inflammation in the blood that, decades later, leads to heart attacks, strokes and cancers - the classic killers of old age ... chronic infections from childhood onward accelerated vascular and other diseases." Suffering chronic disease during childhood - a common state of affairs in past decades - damages your body and thus reduces your chance of a longer, healthier life.
According to the reliability theory of aging, researchers can continue to slowly lengthen healthy life spans through improvements across the board in medical technology for a long while yet. We are not yet close to any mechanical, biological, or complexity-related limits to progress in extending the healthy human life span.
A continuing slow increase in healthy life span - less than a quarter of a year of life span with each passing year of research at the moment - is not very satisfying for me, however. I'd like to be around to see much more of the future in person, which means that the pace of healthy life extension must pick up in decades ahead. This can only happen if many more researchers and funding agencies focus on intervening in the aging process rather than trying to fix the resulting disease and age-related conditions - a grand vision of prevention rather than cure, if you will.
Scientists like Aubrey de Grey are working to make this redirection of scientific focus happen in their fields - but this is the start of a long process. The roadmap for the science itself is fairly clear, at least. Moving beyond incidental life extension is the only way forward if we want to see real results in our lifetimes.