Unfortunately, almost at the same time, the British Journal Lancet published a very large epidemiological study by Bette Liu and colleagues claiming exactly the opposite–that happiness did not affect future death rates.  This was reported on CBS Sunday Morning and elsewhere.  The study contained a number of methodological errors and poor assumptions, and was soon called into question by an OpEd piece in the LA Times, authored by Dr. Diener and his colleagues. I spotted one of the major problems that they referred to and wrote to the author.  It seems that those British women who were unhappiest–those that went to a doctor with complaints and were labelled as depressed or anxious–were considered as having a health problem from the onset of the prospective study, which then examined death rates, and corrected statistically for these health problems.  Dr. Cowan wrote to Dr. Liu, who finally pointed him to a Table (#2) in the Appendix in which you can “see effects”, according to her.  There is at least a 14% improvement in death rate if you are “happy most of the time” rather than unhappy.  So the original finding that enhanced happiness leads to future improved health stands.