Researchers found that women who see the glass as half full are at a lower risk for developing heart disease, and have a lower risk of dying from any cause, than those who see the glass as half empty.  

I am not sure a study actually had to be done, somethings we just know.  Having a positive attitude and seeing the good all around you instead of the bad makes you happier.  Being happy tends to reduce stress, stress is the cause of almost all illness in one way or another. 

If thinking positive is not your natural thought, start to make a point of noticing your negative thoughts.  Once you become aware of the negative you can make a point of looking for the positive and thinking that way. 

By changing your thoughts you really can change your life.  If you think you are just not that kind of a person who can change their thoughts, remind yourself again that it is just a thought.  Thoughts can always change, you have complete control over your thoughts, no matter what is happening in your life, your thoughts are controlled 100% by you.  

I know you can do this, if one person can, then all people can.  By creating thoughts, feelings, and actions you will create the life you have only dared dream.