"The New York Times" reports that the idea that growth hormone can improve "health, energy level and sense of well-being." is a core belief of the A4M, with Klatz writing a book in 1998 entitled "Grow Young with HGH: The Amazing Medically Proven Plan to Reverse Aging" where he states "The ‘Fountain of Youth’ lies within the cells of each of us. All you need to do is release it". A 2005 review in the "Journal of Endocrinological Investigation" noted the long history of these ideas, but stated that the "concept of a 'hormonal fountain of youth' is predominantly mythological." Nevertheless, Klatz maintains that growth hormone reverses aging as a physical process and has described growth hormone as "the first medically proven age-reversal therapy." However, MSNBC reports that Daniel Rudman, the author of the 1990 study that sparked the movement, "issued many caveats and cautions about using HGH and never recommended its use to delay aging. In fact, he was horrified his study was being used to support the industry especially since heavy use of growth hormone can have unwanted side effects".