Here's something for grumps to be happy about: Being unhappy is not going to shorten your life.

Research published in the well-known medical journal Lancet debunks the widespread belief that happy people live longer. Using data from 720,000 women between 50 and 69, scientists found no link between glumness and mortality. Ditto for happy-go-lucky types.

The study, funded by the UK Medical Research Council, followed the women over 10 years, taking note of who died and the cause of death in each case.

Conventional wisdom, based on a slew of other studies, was that a sunny disposition can protect against heart disease and other serious health problems. But the scientists behind the new research say that the previous studies were flawed because they didn't consider that poor health itself can cause unhappiness. Not the other way around. And of course, poor health can lead to death.

"This finding refutes the large effects of unhappiness and stress on mortality that others have claimed," said Sir Richard Peto, an author of the study and a professor of medical statistics and epidemiology at the University of Oxford.

Still, some observers noted that measuring emotions is more nuanced and complex than simply declaring happiness or unhappiness.

"I would have liked to see more discussion of how people translate these complicated feelings into a self-report of happiness," said Baruch Fischhoff, a psychologist at Carnegie Mellon University who studies decisionmaking, who was not involved in the study. "Think about everything that's going on in your life and tell me how happy you are. Happiness is a squishy measure."