According to "The Longevity Project", a study that started in 1922 and kept going until recently, optimism and/or happiness is not the secret to good health and longevity. Not that happiness isn't important, but happy cheerful children were more likely to live shorter lives than those who were more serious or "sober".
You can find out more by reading the book, "The Longevity Project". Chapter 4: "Happiness and Health? A Cheery Conundrum"
