Though laughter is often referred to as "the best medicine," no definitive study has been conducted to determine the effects of laughter on overall human health, leaving open the possibility that maintaining a good sense of humor and a positive attitude are just as important, if not more important, than finding time to laugh each day. But even if laughter is not medicinal, its benefits can mimic those of exercise. When a person laughs, his or her pulse and blood pressure increase, and people tend to breathe faster when they laugh. Faster breathing sends more oxygen to the tissues, which can help the heart and lungs work more efficiently. In addition, a Vanderbilt University study found that between 10 and 15 minutes of laughter can burn as many as 50 calories. Finding time to laugh may also indirectly improve the body's immune system response, as studies have suggested that infection-fighting antibodies might be more abundant in people who can use humor to combat stress.