The survey, funded by GlaxoSmithKline and published in the September issue of the journal Neurology, compared depression rates among epilepsy patients, people with asthma, and people without a chronic disease.
All of the epilepsy patients lived in residential settings, not specialized epilepsy centers.
Alan Ettinger, MD, of Long Island Jewish Medical Center's neurology department in New Hyde Park, N.Y., and colleagues conducted the survey for the Epilepsy Impact Project Group.
The researchers mailed surveys to a sample of U.S. households, receiving responses from 775 people with epilepsy, almost 400 asthma patients, and nearly 360 people with no chronic health conditions.
Close to 12% of the survey respondents without chronic diseases were depressed. That's close to estimates that say nearly one in 10 American adults per year have depression.
Severe depression affected almost 26% of people with epilepsy, compared with 20% of asthma patients and only 5% of those without chronic health conditions.
Lower quality of life and higher unemployment also affected more epilepsy patients than people with asthma.
"Depressed epilepsy patients had worse work, social, and family functioning, were less likely to be employed, and worked fewer days than nondepressed epilepsy patients, adding further evidence of the burden of depression in epilepsy," write the researchers.
Among epilepsy patients, depression was significantly more common among women, low-income patients, and young people.
Depressed epilepsy patients were also more likely to have experienced side effects from their epilepsy medication than those who were not depressed.
Compared with asthma patients or those without a chronic medical condition, people with epilepsy were more likely to have sought help for depression or taken antidepressants in the past.
However, many cases of depression went untreated.
More than 38% of depressed epilepsy patients and more than 43% of depressed asthma patients had never been evaluated for depression before taking the survey.
The numbers are "disturbing," say the researchers.
Ettinger and colleagues urge doctors and epilepsy patients to discuss depression and consider possible depressive effects of medication.
People with epilepsy may experience depression differently, with "high rates of irritability, anxiety, and a tendency toward alternation with occasional euphoric periods" seen in a previous study, say the researchers.
Of course, anyone experiencing symptoms of depression should also seek treatment. Not sure if you're affected? A health care provider must make the diagnosis. WebMD's confidential depression screening tool, "Are You Depressed?" may help as a first step.