Most people believe that being positive is good for you. But psychologists Sarah Pressman and Sheldon Cohen at Carnegie Mellon University in the United States have just published an article which flies in the face of the accepted wisdom that it's good to "have a nice day".
The review, published in the journal Psychological Bulletin, expresses concern that there are about 20 times more psychological studies on depression and health than there are on happiness and health, and suggests we need to understand more about the latter - because it's long-term impact on us may not always be positive.
A study published in the early 1990s found that positive mood in gifted children was associated with higher rates of early mortality in adult life.
This sobering and counterintuitive conclusion might be the result of optimistic and cheerful people underestimating dangers, taking risks or failing to follow medical advice. Previous research indeed confirms that happy, healthy individuals perceive themselves as less vulnerable to negative events. Pressman and Cohen note that those in the study at greatest risk of an early death scored in the "extremely happy" range, in contrast to those with a lower risk who averaged merely "very happy".
The influence of a positive attitude may also be dependent on age, setting negative health trajectories in early life but positive ones in later life.
Research carried out among elderly people living in the community, rather than in institutions such as nursing homes, suggests that positive mood is indeed associated with greater longevity.
Yet Pressman and Cohen point out that studies of older people in nursing homes produced quite different findings. Here, increased wellbeing was paradoxically associated with increased likelihood of death. There is evidence that older people who are demanding, aggressive and narcissistic are most likely to survive a move to a nursing home. A bad temper may reflect a fighting spirit in a situation of lost control.
Whatever the final answer to this intriguing cluster of findings, it seems that happy is not always the best mood to be in, particularly if you want to live long. It's a tough choice: a long, miserable life, or a short, happy one?
Dr Raj Persaud is consultant psychiatrist at the Maudsley Hospital in south London and Gresham professor for public understanding of psychiatry. His latest book is The Motivated Mind (Bantam Press). Email: email@example.com