Dr. Dean Edell (who is a medical doctor who has actually practiced) wrote a book where he suggests that it is useless to deprive yourself only to live a few more years. He says that if you are 90 and suffering from the traditional ailments of age, you will hate having to go on living and putting up with all the problems.
He suggests that if you live it up (within reason) when you are younger, then you will die happy.
I think for the most part this is valid. If I was old and frail and my memory and cognative skills were fading, I would not want to prolong that lifestyle. On the other hand, if I lived a full life, then I would likely die earlier (such as by a heart attack or organ failure) before I would experience things like Alzheimers.
The human body was not meant to go on forever and I think there is little benefit in pushing it too far.
As the cliche goes... No one ever regretted working too little.