People who feel depressed and fatigued may not be more likely to develop cancer than their perkier peers, Danish researchers report.

It's a topic that has drawn attention in the public and in the scientific community, write Corinna Bergelt, PhD, and colleagues in the journal Cancer.

The most tired, depressed participants in Bergelt's study weren't more likely to be diagnosed with cancer than those at the other end of the spectrum.

However, the most tired, depressed people were more likely to have unhealthy habits (such as smoking and physical inactivity), write the researchers.

Depression and Health

Depression is a serious illness that affects the body, mood, and thoughts. Nearly 19 million U.S. adults per year have depression, according to the National Institute of Mental Health's web site.

Depression is treatable. Left unchecked, it has been linked to heart disease and other health problems.For instance, depressed heart attack survivors have been found to have a higher risk of death or have more heart problems in the two years after their heart attack compared with those without depression.

Studies about depression and cancer have had mixed results, writes Bergelt, who works at the Danish Cancer Society. For instance, a study in October 2004 showed that people with mental disorders, including depression, were more likelyto develop certain cancers at younger ages.

Read WebMD's "Your Guide to Depression"

Examining Exhaustion

The study included more than 8,500 adults enrolled in a Danish heart disease study.

At the study's start, participants were 21-94 years old and didn't have cancer. They took surveys checking for "vital exhaustion," which includes feeling depressed and fatigued.

The survey was designed for heart disease studies. It didn't specifically screen for clinical depression, but topics were similar (such as feeling hopeless, listless, or tearful).

The most exhausted group included 28% of female participants and 18% of the study's men.

Read WebMD's "Quiz: Could You Be Depressed?"

No Cancer Link

Participants were followed for 8.5 years on average. During that time, 12% of them (976 people) were diagnosed with cancer.

The researchers found no link between cancer and the most severe cases of vital exhaustion. In fact, the most severely exhausted people actually had a lower risk of cancer than the least exhausted participants.

Poorer Health Habits

People with high exhaustion scores (especially the most exhausted people) had a less-than-healthy profile.

They were more likely to use a lot of tobacco, live alone, earn less money, have less school education, and be physically inactive than the least exhausted participants, write the researchers.

After taking all of that into consideration, Bergelt and colleagues write that the results "show that a state of high vital exhaustion is associated with an unhealthy lifestyle. Nevertheless, vital exhaustion itself is not associated with an increased risk of cancer."

Read WebMD's "Exercise for Depression Rivals Drugs, Therapy"

The Fine Print

The study was large, long, and had a high follow-up rate, write the researchers. However, they note a few limits.

Depression and fatigue were only measured once, at the study's start. Participants' energy level and mental health could have changed over the years, for better or worse. Screening participants several times might zero in on people with persistent fatigue and depression.

Healthy people might have been more likely to enroll in the study. Since the original study focused on the heart, those with other health problems may not have been interested.

It's also possible that some of the most severely exhausted participants died of another health problem before developing cancer, write the researchers.

Still, they write that the findings "do not support the hypothesis that subclinical depressive feelings, as measured by the vital exhaustion questionnaire, increase the risk for developing cancer."

By Miranda Hitti, reviewed by Brunilda Nazario, MD

SOURCES: Bergelt, C. Cancer online edition, Aug. 8, 2005. National Institute of Mental Health: "Depression." WebMD Feature: "Many Emotions Can Damage the Heart." WebMD Medical News: "Depression Dangerous After Heart Attack." WebMD Medical News: "Mental Health Linked to Cancer Risk." News release, John Wiley & Sons, Inc.