The approach was shown to be successful for patients with a variety of illnesses including coronary artery disease, high blood pressure and asthma - helping the patients to stick to their treatments.
These findings are the result of three studies of 756 patients. They are the first large, randomised controlled trials to show that people can use positive thoughts and self-affirmation to help them make and sustain behaviour change.
The research was funded by a 9.5 million dollar contract from the National Heart, Lung and Blood Institute of the National Institutes of Health and led by Dr Mary Charlson, from Weill Cornell Medical College.
In all three studies, patients were encouraged to think of small things in their lives that make them feel good (such as seeing a beautiful sunrise) when they got up in the morning and throughout their day.
They were also asked to use of self-affirmation to help them overcome obstacles to getting better by recalling moments in their lives they were proud of, such as a graduation.
"This simple approach gives patients the tools that help them fulfil their promise to themselves that they will do what's needed for their health," the Daily Mail quoted Dr Charlson as saying.
"For example, if it's raining and they don't feel like exercising, these strategies can help them get past this mental block and into their sneakers," she said.
A script was given to those taking part in the study that read: 'First, when you get up in the morning, think about the small things that you said make you feel good'.
It then let the participant choose their own happy thought, or gave some unusually specific examples including 'babies in hats' or 'the sunrise'.
It continued: 'As you go through your day, notice those and other small things that make you feel good and take a moment to enjoy them.
'Second, when you encounter some difficulties or are in a situation that makes it hard for you (eg taking your blood pressure medications or exercising), think about things you enjoy or proud moments in your life.'
Patients in the study were randomly assigned either to the experimental 'positive affect' group or to a control group.
Both groups made personal contracts to adhere to their behaviour plans, were given an educational guide on the importance of their intervention. They received phone calls every two months to check in on their progress.
Along with daily use of positive thinking, patients in the experimental group received surprise gifts like tote bags prior to the phone sessions.
The monetary value of the gifts was unimportant, rather they were symbolic and served to reinforce the intervention, Dr Charlson said.
Results were measured at the end of the yearlong studies.
For coronary artery disease, 55 per cent of patients in the positive thinking and self-affirmation category increased their physical activity compared with 37 percent in the control group.
The positive affect group also walked an average of 3.4 miles a week more than the control group.
For high blood pressure (the study focused on African-Americans with the disease), 42 per cent of the positive thinking group adhered to their medication plan compared with 36 per cent in the control group.
"Positive affect made a real difference - patients are better able to follow through on behaviours to improve their health," said Dr Charlson.
The results were published online in the January 23 edition of the Archives of Internal Medicine.