A spoonful of hope might not be the best medicine, according to a new study from a Carnegie Mellon University professor that asserts that optimism can actually be harmful to mental health.

The study, authored by CMU's George Loewenstein and several researchers at the University of Michigan, measured the emotional well-being of patients in two groups: those with permanent colostomies and those with colostomies that might be reversed.

A colostomy is a surgical procedure -- either temporary or permanent -- resulting in feces leaving a patient's body through the abdomen. Though patients with reversible colostomies initially reported higher life satisfaction, they grew less happy as time went on, whereas patients with irreversible colostomies became happier over a six-month period.

"We usually assume that hope is a good thing and that it's better to have the possibility of relief," said Dr. Loewenstein, explaining the "paradoxical" findings in the study, published this week in the Health Psychology journal. "But, we found that hope has a major downside and can prevent happiness."

The finding mirrors anecdotal evidence in situations that are somewhat analogous, he said, such as reports that prisoners who have a chance at parole seem to be more miserable than those with a fixed sentence. He also offered the example of parents with a child who is missing and presumed dead being more distraught than parents of a child whose death is certain.

The reason that hope might lead to more misery might be because our brains are resistant to adaptation unless we know that it is definitely necessary.

"Adaptation takes work, it takes effort," he said. "Unless you are sure that your condition is permanent, you don't bother to put in that effort."

Though patients with irreversible colostomies might have a permanent medical condition, they also have closure, said Dr. Loewenstein, which allows them to move on with their lives.

Though doctors generally prefer to deliver good news, the study suggests that they should not be excessively optimistic when they inform patients about their prognosis, he said.

The findings also reinforce the idea that happiness is dependent on more than just life circumstances.

"Happiness is a state of mind," he said. "It's not about how wealthy you are, how healthy you are. By showing that a group of people who are clearly objectively worse off are substantially happier, it just underlines that reality that happiness and unhappiness are much more in our minds."

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