People who are depressed and fatigued have a higher risk of heart attacks and other cardiac problems. Many people assume the same holds true for cancer. Perhaps being depressed and tired deals a blow to the immune system, making a person more vulnerable. But now a study of several thousand people has shown there's no link, dealing a blow to the theory of a "cancer prone" personality.

The study, published in the most recent issue of Cancer, looked at the medical records of more than 8,500 Danish people. Researchers gave each one a score for "vital exhaustion"–feelings of excessive fatigue, lack of energy, increased irritability, and demoralization. That's the same state that has been shown to increase the odds of a heart attack and death. The scientists then followed up those people for nearly nine years, on average, to see if they got cancer.

There was no significant link, they say, between the score and any risk for these cancers:

• Cancers of any particular part of the body
• Alcohol-related cancers
• Hormone-related cancers
• Cancers related to viruses or immune function

That last item puts a hole in the theory that lowered immune defenses from depression and fatigue open the door to cancer. And the whole study adds to the evidence that the idea of a "cancer personality"–certain traits that make you more likely to get the disease–is a myth.

"Personality per se–grief, depression–these factors do not make you more vulnerable to cancer," says Jimmie Holland, a psychiatric oncologist at Memorial Sloan-Kettering Cancer Center in New York.

Not only is the idea of a cancer personality scientifically inaccurate, Holland says; it often leads people with the disease to blame themselves and feel that they must have a positive attitude all the time to avoid a recurrence.

That's not to say that vitally exhausted people are healthy. Those with the highest exhaustion scores tended to have unhealthier lifestyles, including low physical activity and higher tobacco use. So it's possible that a case of the blues may have other, potentially serious consequences.