The perennial temptation to blame disease on sin or at least some grave moral failing just took another hit. A major new study shows that women on a virtuous low fat diet with an extraordinary abundance of fruits and veggies were no less likely to die of breast cancer than women who grazed more freely. Media around the world have picked up on the finding, cautioning, prudishly, that you can’t beat breast cancer with cheeseburgers and beer.

Another “null result” in cancer studies–i.e., one showing that a suspected correlation isn’t there–has received a lot less attention. In the May issue of Psychological Bulletin, James Coyne and his colleagues at the University of Pennsylvania reported that “there is no compelling evidence linking psychotherapy or support groups with survival among cancer patients.” This flies in the face of the received wisdom that any sufficiently sunny-tempered person can beat cancer simply with a “positive attitude.” For example, an e-zine article entitled “Breast Cancer Prevention Tips” advises:

A simple positive and optimistic attitude has been shown to reduce the risk of cancer. This will sound amazing to many people; however, it will suffice to explain that several medical studies have demonstrated the link between a positive attitude and an improved immune system. Laughter and humor has [sic] been shown to enhance the body’s immunity and prevents against cancer and other diseases. You must have heard the slogan “happy people don’t fall sick.”

So far no one appears to have read Coyne’s study. On June 30, a month after its publication, all-purpose guru Deepak Chopra assured Sanjay Gupta on CNN that the mind can control the body: “…You know, of course, the … study where women who supported each other in a loving environment with breast cancer, the survival doubled.” Gupta, last sighted seeking to discredit Michael Moore’s Sicko with his “fact- checking,” simply nodded, although the study Chopra was referring to was discredited years before Coyne’s research came out.

For the last decade or so, adherents of the new discipline of “positive psychology” have been insisting that not just cancer, but almost any health setback, can be conquered with optimism or a “positive attitude.” But as Coyne and other critics point out, the science here is shaky at best. Even the theoretical lynchpin of the supposed happy mind-healthy body connection–that a positive outlook strengthens the immune system–took a kick in the teeth two years ago when Suzanne Segerstrom at the University of Kentucky found, to her own apparent surprise, that optimism can have a negative effect on the immune system when the stressors are intense, as in the case of serious disease.

Even if veggies and smiles don’t cure cancer, aren’t we still entitled to blame some people for their diseases? Lack of exercise and dietary indiscretions play a role in the development of diabetes and coronary heart disease, so we indulge in self-gratifying contempt for the fat lady scarfing down Doritos. But before you rush to judgment, ask yourself: What nutritional alternatives does she have? (And, yes, I know they have “salad” at Wendy’s now, but they don’t offer apples on Amtrak.) As for exercise, gym memberships easily cost $500 a year, and far too many of us are forced to spend ten hours or more a day sitting in a cubicle, a car or a bus.

In the case of breast cancer, one victim-blaming theory after has wilted under scrutiny: The “cancer personality” theory, for example, which breast cancer victim Susan Sontag took on in her 1978 book Illness as Metaphor, and now high-fat diets and negative attitudes. Something other than genetics causes it, though, and one leading candidate is the hormone replacement therapy that doctors pushed on menopausal women for decades as a supposed way of preventing heart disease, Alzheimer’s and wrinkles. When, in 2002, HRT was found to be correlated with breast cancer and millions of women stopped taking it, the incidence of breast cancer plunged.

Which suggests that optimism, especially about the validity of the conventional wisdom, can be hazardous. What you need is a narrow-eyed, deeply skeptical attitude.