Here is a new book I found recently, and it is well worth reading.
The author takes on the claim that religion is proven to be good for your health. The book show why these claims misrepresent the scientific literature. The claimed studies often fail to take other factors into consideration, or they commit the "sharpshooters fallacy" in which they search the data for any combination that suggests that religion promotes health, while ignoring the majority of the data. This book is a good introduction to the methods of scieintific inquiry into medical claims. It shows why we should not be led by false claims of cures.
Chapter 9 debunking the claimed effects of long-distance prayer is particularly important.
I recommend this book.
(Click here to see more about it.)