Read enough self-help books and you'll probably be convinced that your outlook on life has extraordinary power. Stay happy and optimistic and the universe will reward you with success, love, even long life, many of these authors suggest. And sorry grumpy folks, but by the same scheme, the miserable are bringing some of their misfortune on themselves. Just cheer up and you'll be healthier and more successful.

It all sounds appealingly straightforward and empowering, but is it actually true? The relationship between happiness and success may stand, but according to a new, huge, and fairly definitive study published in The Lancet, the bit about happiness and physical health is pretty much total bunk.

Sorry self-help gurus, but being cheerful won't bring you a longer life.

Being sick will make you miserable but not the other way around

The study followed nearly a million middle-aged British women for ten years, recording their self-reported happiness and their mortality, as well as various measures of health. To see if happiness and good health were related, the researchers compared the outcomes of happy and unhappy women who started the study in good health over a ten year period. If you were initially hale and hearty, did being stressed and miserable make you more likely to get sick or die prematurely?

Nope, the data show mood had basically no effect on health outcomes. Study author Sir Richard Peto, who is a professor of medical statistics and epidemiology at the University of Oxford, called the results, "good news for the grumpy."

The results might cheer those with a less-than-sunny disposition, but it will confound some other researchers in the field whose previous studies showed a correlation between happiness and health. What went wrong with that earlier research? "In our view, the previous studies haven't been well done," Peto said. "All that's going on is ill health actually was causing unhappiness and stress."

The findings will be at least a bit of a bright spot for those suffering with unhappiness. They have enough to worry about without feeling that their emotional state is likely contributing to their premature death as well. "Believing things that aren't true isn't a good idea," Peto declared in an interview with the New York Times. "There are enough scare stories about health."

A few caveats

As with any study, experts have noted some limitations of the research. For instance, the data relies on self-reported happiness levels, which are generally less reliable than other more complicated measures of mood. Others note that people often do some pretty unhealthy things, like increase their drinking or wallow on the couch with a bag of Cheetos, to cope with unhappiness, and these behaviors could shorten your lifespan.

But these caveats aside, most commentators agree that the study is fairly definitive. "This new data is solid proof that people who are depressed, anxious, or stressed need not pile on more guilt and worry because they think they're bringing about their own demise," concludes Christina Cauterucci on Slate.