Imagine there is a glass of water on a table in front of you. It has water in it but it is not full. How do you describe the glass? Do you say it is half full or half empty?

If you say half full, you might be an optimist. If you say, half empty, you might be the opposite -- a pessimist.

Optimism and pessimism represent your general attitude toward certain situations or to life in general. And your attitude about life may be more important to living than you think.

A new study suggests that your level of optimism may affect your health. People who are optimistic may live longer than those who are pessimistic.

Researchers at Harvard University’s School of Public Health in Boston did the study. They compared women with "a general expectation that good things will happen" to women who were less optimistic.

They found that the optimists had a much lower risk of getting several deadly diseases, including cancer, heart disease, stroke, respiratory disease and certain types of infection.

The researchers published their findings in the American Journal of Epidemiology. Epidemiology is the study of how diseases spread and how they can be controlled.

Eric Kim is one of the study leaders. He says there is increasing evidence that strengthening psychological resilience may help prevent disease. Resilience is the ability to recover from difficulty or change. Kim says that these new findings suggest that people should make efforts to increase their resilience and optimism.

He says optimism is connected with healthier behaviors and healthier ways of dealing with difficulty. Optimists tend to take better care of themselves by exercising, eating healthy foods and getting enough sleep.

However, the researchers say that healthy behaviors of optimistic people only partly explain the connection with reduced risk of disease.

For the study, researchers looked at information gathered on 70,000 women in the Nurse's Health Study. This massive study began in 1975. It collects health information on those involved in the study every two years.

The Harvard researchers looked at the level of optimism of the women, as well as other factors such as race, diet, physical activity level and overall health.

They found the most optimistic women had nearly a 30 percent lower risk of dying from disease. When compared to the least optimistic women in the study, the optimistic women had:

an almost forty percent lower risk of dying from heart disease, stroke and respiratory disease, a fifty percent lower risk of dying from infection, and a sixteen percent lower risk of dying from cancer.

The researchers note that other studies have linked optimism with reduced risk of death from cardiovascular disease. This, however, is the first study to link optimism with reduced mortality from other diseases.

Kaitlin Hagan, another study leader, says earlier studies show that a person can use simple, low-cost methods to increase optimism. For example, she says people can think about and write down the best possible outcomes for areas of their lives, like their careers or relationships.

Leslie Ralph is a clinical psychologist and counselor at the University of Arizona in Tucson. She also blogs about stress management. Ralph has several ideas about how to increase optimism.

She says each night plan to do two or three simple, enjoyable activities the next day. These activities might include watching the sun rise, visiting a friend, dancing to a favorite song or reading a story with your child.

She also suggests that if your day starts badly, simply close your eyes for a moment and take a deep breath. When you open your eyes, imagine your day has started over. It’s like having your own restart button.

And the counselor adds offering praise or support to someone can also improve your own outlook. A smile and “thank you” from another person may help you feel more optimistic.