Unforgiveness is a complex mixture of thoughts, attitudes, beliefs and emotions involving a feeling of injustice. If a person transgresses another they can find it very difficult to offer the transgressor their unconditional forgiveness. Dr. E. Worthington hypothesises that a feeling of injustice can cause stress reactions in the body which in turn can affect immune system dysfunctionality.

 If this conceptualisation is correct it implicates a whole range of correlations between stress and immune response. This is demonstrated by many psychoneuroimmunology research projects and in particular, research conducted by Kiecolt-Glaser et al (2002). They found that a high level of stress significantly correlated with immune dysregulation.

            Dr Everett L. Worthington, a psychology professor at Virginia Commonwealth University, found that people who do not forgive others have a higher number of health indicators such as cardiovascular diseases & stress related disorders. It is important to note that as well as physiological health problems, he found that people who don’t forgive tend to have more psychological problems which can result in higher rates of divorce and poor social interaction.

            In addition to this, Worthington proposed that people who do practice forgiveness, on average, are less depressed, have longer marriages and better support from their friends and family. Those who forgive tend to have better social support systems, which has in turn been linked to improved mental wellbeing.

            Various psychological interventions have been developed to help people to forgive others. Lundahl, Taylor, Stevenson and Roberts (2008) conducted a meta-analytical review of 14 forgiveness interventions which included a comparison group. The result were that samples that received forgiveness interventions forgave more and enjoyed increased positive affect and self-esteem and less negative affect. They found that these gains were largely maintained at follow-up periods. Individually delivered programs were superior to group delivery.

            Looking at physical health, Lawler et all (2003) measured 108 college students for two types of forgiveness: 'trait forgiveness' and 'state forgiveness'. Trait forgiveness measures how forgiving a person is in general, whereas state forgiveness looks at how recalling a specific betrayal situation, affects the individual.

            Students with high trait forgiveness averaged a lower blood pressure, than those with a low trait forgiveness. Additionally, those who had forgiving personalities displayed better state forgiveness which meant, when a betrayal event was brought up in conversation, their stress arousal response returned to normal faster than those who tended not to forgive.

            An interesting expansion of this was undertaken Toussaint et al (2001) who interviewed 1,423 Americans, making it one of the largest forgiveness studies to date.

            They rated each participant in terms of how forgiving they were and collected health data from them. The results showed that those who were rated as having a more forgiving personality, were generally healthier than grudge holders.

            Accumulating evidence supports the idea that, by forgiving others, an improvement in a persons health and wellbeing, both physiologically and psychologically can be found.

           Worthington has written a textbook on forgiveness which acts to summarise recent studies and give an overview of their findings and what implications these findings could have. It is called the 'Handbook of forgiveness'. Chapter 19 of the book, which relates particularly to health matters, can be found online for free here 'Forgiveness, Unforgiveness, Health and Disease'

Here is a link to a talk on how 'studies suggest forgiveness has health benefits'

Finally, if you require any more information on research which has been undertaken into this area, there is a good bibliography of forgiveness research at http://www.forgiving.org/Campaign/Forgiveness_Bibliography.pdf