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But another hunch turned out to be far more productive. When Snowdon and Kemper first read the sisters' autobiographies in the early 1990s, they noted that the writings differed not just in the density of ideas they contained but also in their emotional content. "At the time," he says, "we saw that idea density was much more related to later cognitive ability. But we also knew that there was something interesting going on with emotions." Studies by other scientists had shown that anger and depression can play a role in heart disease, so the team decided to take another look.
This time they searched for words suggesting positive emotions (such as happiness, love, hope, gratitude and contentment), as well as negative ones (sadness, fear, confusion and shame). Snowdon found that the sisters expressing negative emotions did not live as long as the sisters conveying more positive ones. He has already begun another analysis, comparing the emotional content of the nuns' early autobiographies with the ones they penned in late life, as part of the Nun Study. As mental abilities decline, his preliminary review has found, the expression of positive emotions also drops. While he suspects the whittling away of positive feelings are a consequence of the neurological changes of Alzheimer's, it is still possible that emotional states may play a role in determining cognitive function. To find out, Snowdon will next compare the emotional content of the sisters' writings with their autopsied brains, to see if positive emotions work to keep nerve connections snapping and if negative emotions dampen and eventually extinguish them.
By now, 15 years after he first climbed Good Counsel Hill, Snowdon has identified half a dozen factors that may predict or contribute to Alzheimer's disease. He could sit each sister down right now and tell her what her chances are. But should he? As he has all along, Snowdon will put his dilemma to the sisters themselves: next month he will meet with the Notre Dame leadership to discuss whether to break the news to the high-risk nuns--and how to answer the inevitable questions about what they might do to prevent or slow down the disease.
"So far," he says, "I have a certain comfort level in making some recommendations because there are other good reasons for preventing strokes, for reading, for taking folic acid. If our findings showed something that had no other known benefit besides preventing Alzheimer's, then we would be on much thinner ice." Even so, it's not clear precisely how much folic acid to take, and Snowdon's team is divided on whether to boost the intake of vitamins C and E beyond the normal recommended doses (Markesbery says yes; Snowdon says not until we know more).