There’s been lots of research on this subject in form different angles ( ie’ the relationship between happiness and cancer or heart disease) but its difficult to do really good double blinded studies. Some of the research has seemed to show some benefits and others have not. Most of the studies are retrospective and very few use random assignment of subjects without which there is a strong probability that the results will be tainted by confounding variables. Most of the studies are just pure garbage though.
That being said there are at least two ways to look at this. On the one hand there may be little harm when you try to get people to have a positive outlook on life and even if their disease does not respond they may gain some other benefit from it ( like feeling less depressed). On the other hand you may give people false hope and when their cancer does not respond or they get cancer when they were trying to prevent it they may become even more despondent and hopeless than they otherwise would have.
I think the main problem I have with all of this is something I have complained in frequent and varied venues. Its the fact that the medical establishment is selling out science for the sake of profits. Even honored institutions like Harvard and Mass General have been “wooed” to the dark side and promote things that are unscientific which only further dumbs down the scientific literacy of this country.
If some new age motivational speaker wants to promote this stuff its one thing but I think its extremely unprofessional for the medical community to be doing it. Thats what happens though when the “suits” start calling the shots at hospitals. Now that most hospitals are part of big corporations its going to be happening more and more. I keep saying it but good medical care should give patients what they need and NOT what they want. Businesses need to have exactly the opposite philosophy. When hospitals become big business as they are these days one of these models has to be discarded and Im afraid the business model is the one thats winning.