"In numerous studies of cancer, the most consistently identified risk factor is the inability to express emotion, particularly the feelings associated with anger. The repression of anger is not an abstract emotional trait that mysteriously leads to disease. It is a major risk factor because it increases physiological stress on the organism. It does not act alone but in conjunction with other risk factors that are likely to accompany it, such as hopelessness and lack of social support. The person who does not feel or express "negative" emotion will be isolated even if surrounded by friends, because his real self is not seen. The sense of hopelessness follows from the chronic inability to be true to oneself on the deepest level. And hopelessness leads to helplessness, since nothing one can do is perceived as making any difference."
A fragment of the book "When the body says no: the cost of hidden stress" by Dr. Gabor Maté.