The study was the culmination of a 15-year study on aging and Alzheimer's disease that was published in the Journal of Personality and Social Psychology.

Since 1986, 678 school nuns were "tracked" … they received annual physical examinations, mental assessments and laboratory blood tests. Also, each sister agreed to donate their brains to the team of researchers at the time of their deaths.

An interesting discovery showed that stroke and head injuries can increase the risk of Alzheimer's and folic acid appears to counteract it.

The study included an analysis of autobiographies that were written by the nuns in their early 20's … elderly sisters who displayed positive emotional states were not as prone to display the signs of Alzheimer's as they age. Researchers were actually able to predict those that would end up with Alzheimer's some 60 years later with an 85% - 90% accuracy.

The conclusion alluded to is that ... negative emotions like hatred, distress, anger, etcetera can eat away at a person little-by-little and ultimately lead to heart disease and stroke.

More information can be found in the book Aging With Grace: What the Nun Study Teaches Us About Leading Longer; Healthier and More Meaningful Lives.