From Good Magazine:
For thousands of years the world’s religions have been preaching—if not always practicing—forgiveness. Now the medical community is finding that there are more benefits to letting things go than just better relationships and peace of mind. As the results of long-term studies on the physiological impacts of forgiveness trickle in, the evidence is stacking up behind a single idea: Truly forgiving those who have wronged us is good for our health in myriad ways—it lowers blood pressure, improves sleep, and increases life span.
Medical research on forgiveness is a relatively new field, with the first real study appearing in the late 1980s, but as more and more researchers examine the physiological impacts of forgiveness, the idea that it can be a powerful tool in healing is gaining support. Multiple medical studies have found that people who have forgiven others for a major transgression have lower blood pressure and heart rates when compared to those who have not. Kathleen Lawler-Row, who heads up the psychology department at East Carolina University, has studied the effects of both hostility and forgiveness on the body’s systems extensively. In a 2005 study, she found that sleep quality—which has a known effect on various bodily systems—was positively correlated with forgiveness and negatively correlated with the motivation for revenge. In other words, forgiving someone will make you sleep better at night, but holding on to resentment is likely to lead to insomnia.