But they cannot increase the duration of life, because people have acquired their bodies by a superior arrangement. You have this body, and you must live within it for a certain period. If you simply change one of the parts of your body, that will not help you prolong your life. That is impossible. The doctors think that by changing the heart they will increase the duration of life, but that is not possible.(PRABHUPADA QUOTE)
Ayurveda is the science of life and longevity.The basic idea being if you align yourself with these principles you can live a long and healthy life.That seems very reasonable as we can see by neglegting these principles people unneccesarily shorten both the quality and quantity of there lives(drug abusers etc.)
How do we harmonize this with Prabhupada's statement? Any ideas anyone?
According to the yogic world view one's life is determined by the number of breaths on is alloted by one's karma. With one's final exhalation the soul leaves the body through the mouth. It may be possible to seemingly increase one's duration of life by regulating one's breathing, pranayama, changing one's lifestyle, not smoking, etc. but it is not possible to change the number of breaths one is alloted.
Ayurveda is primarily concerned with improving the quality of one's life, which may also increase the number of years one lives without increasing one's alloted number of breaths. Interestingly, yoga practice has much to do with breath. Otherwise I am not sure that Ayurveda speaks much about increasing the duration of one's life. It is the vedic "Life Science"—ayur = life veda = science, and not the longevity science.