LEXINGTON, Ky. (AP) - If you're happy and you know it - you just may live longer.

New research released Monday stemming from a 15-year study of aging and Alzheimer's disease in nuns suggests a positive emotional state at an early age may help ward off disease and even prolong life.

``It's been known for years that pathological expressions of emotion like depression or hostility can lead to illness,'' said David Snowdon, University of Kentucky professor of neurology and director of the Nun Study for the school's Sanders-Brown Center on Aging.

``Our theory is that negative emotional states such as anxiety, hatred and anger can have a cumulative effect on the body over time. Over decades and decades, people that turn these negative emotions on and off several times daily are hurting themselves and are more likely to fall victim to heart disease and stroke.''

Snowdon's findings were published Monday in The Journal of Personality and Social Psychology.

``It's interesting research and it's important research,'' said Dr. Richard Suzman, an associate director at the National Institute on Aging. ``I believe this most recent finding that optimism can predict and even aid longevity will lead to a lot of further study in this area.''

Since 1986, Snowdon has carefully tracked participants in the study, who all are members of the School Sisters of Notre Dame. All 678 agreed to annual cognitive and physical assessments, blood tests and the donation of their brains to the research team upon death.

The study has produced evidence that stroke or head trauma can increase a person's chances of suffering from dementia or Alzheimer's disease later in life. It also has shown that folic acid may help fight the ravaging affects of the disease, which robs the elderly of cognitive function before killing them.

Several years ago, Snowdon and his colleagues analyzed 180 autobiographies written by the nuns in their early 20s. They found that the elderly sisters who expressed themselves at a more complex level in their earlier essays were less likely to show signs of Alzheimer's disease as they aged.

``We learned that by looking at early mental function, we could predict with 85 to 90 percent accuracy which ones would show brain damage typical with Alzheimer's 60 years later,'' said Snowdon, 48, whose book on the Nun Study, ``Aging With Grace: What the Nun Study Teaches Us About Leading Longer, Healthier and More Meaningful Lives,'' was scheduled for release Tuesday.

Now, after poring over the autobiographies again and looking for key words such as ``happy,'' ``joy,'' ``love,'' ``hopeful'' and ``content'' Snowdon has found that the nuns that articulated more positive emotions lived as much as 10 years longer than those expressing fewer positive emotions.

``That goes along with other studies that have shown that people who rated more positive on personality tests were more likely to live longer than those who were more pessimistic,'' Snowdon said. ``The more optimistic a person is, the less stress that person puts on his or her body over time.''

Acknowledging that negative emotions can have an adverse effect on longevity and learning to manage these feelings is important to leading a longer, healthier life, Snowdon said.

``It feels good to be happy and hopeful,'' he said. ``It's an enjoyable state that produces very little stress, and the body thrives in those conditions. It's one more thing that people can do for themselves to try to stay healthy.''

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