But there’s no evidence to back up the idea that an upbeat attitude can prevent any illness or help someone recover from one more readily. On the contrary, a recently completed study of nearly 60,000 people in Finland and Sweden who were followed for almost 30 years found no significant association between personality traits and the likelihood of developing or surviving cancer. Cancer doesn’t care if we’re good or bad, virtuous or vicious, compassionate or inconsiderate. Neither does heart disease or AIDS or any other illness or injury.
- from here.