TUESDAY, Dec. 7 (HealthDay News) -- Smokers trying kick the addiction are less likely to be successful if they're depressed, says a new study.

Researchers surveyed callers to the California Smokers' Helpline and found that 24 percent had major depression and 17 percent had mild depression. More than half of the smokers had made an attempt to quit smoking after calling the hotline.

After two months, the rate of success of smokers with major depression was far lower than that of smokers who were mildly depressed or not depressed. Of those who tried to stop smoking, around one in five with major depression had been able to quit and stay smoke-free, compared to nearly one in three people in the other two groups.

The findings appear online and in the January 2011 print issue of the American Journal of Preventive Medicine.

It was already known that mild depression reduces smokers' chances of quitting. This study suggests that major depression has an even greater impact. But most smoking hotlines -- also known as quitlines -- do not evaluate smokers for depression, the researchers noted.

More than 400,000 smokers in the United States call smoking quitlines each year. Based on their findings, the study authors estimated that up to 100,000 depressed smokers are not receiving the targeted treatment they require.

"Assessing for depression can predict if a smoker will quit successfully, but the assessment would be more valuable if it were linked to services" that address both smoking and depression, lead author Kiandra Hebert, of the University of California at San Diego, said in a Center for Advancing Health news release.

More information

The American Cancer Society offers a guide to quitting smoking.