People with cancer who are depressed are more likely to die than are patients with good mental health, psychologists reported on Monday in the science journal Cancer.

The study reported that death rates from cancer “were up to 25% higher in patients experiencing depressive symptoms and up to 39% higher in patients diagnosed with major or minor depression.”

“In both of those groups, you can predict cancer mortality,” lead researcher Jillian Satin, of the University of British Columbia here, said.

While the study’s main conclusion is a call for more research on the links between cancer and mental health, Satin said the results also proves the link is significant. “I think depression should always be taken seriously,” she added. “It would be my wish that this line of research fuels adding psychological social treatment into standard cancer care.”

The study by Satin and co-authors Wolfgang Linden and Melanie Phillips was an overview, called a meta-analysis, of 26 previous studies on the effect of depression on the progression of cancer and survival rates in of 9,417 patients.

Satin said the researchers controlled for the chicken-or-egg factor: Do people become depressed because they are
sick with cancer? Or does cancer kill them more often when they have depression independent of the cancer?

“That’s the million-dollar question,” she said. “Even after correcting for that, we still see the positive relationship between depression predicting mortality.” But Satin warned, “I want people to be cautious about this. We have not shown that depression itself causes mortality — but we have a suggestion that this is possible.”