At the End of Life
There is a difference between living a long and fulfilling life as a result of lifelong healthly lifestyle, quite another to have your life unnecessarily prolonged when you are sick and clearly beyond cure. The first is desirable, though not guaranteed; the second is a sorry way to exit the world. See also Palliative care
In the Middle of Life
See the collection of evidence-based advice on Bandolier http://www.jr2.ox.ac.uk/bandolier/booth/booths/hliving.html.
At the Beginning of Life
See Infant mortality