Many people with chronic obstructive lung disease (COPD) also suffer from depression, and now a new study finds this problem can impact their treatment.

With a prevalence of 17 to 44 percent, depression remains one of the most common, yet least recognized and under-treated, co-morbidities among patients with COPD, University of Maryland researchers say.

COPD is the third leading cause of death in the U.S.  More than 11 million Americans have been diagnosed with depression, but an estimated 24 million may have the disease but be unaware of it, statistics say.

The researchers obtained Medicare administrative claims data and assessed a five percent random sample of Medicare beneficiaries (average age 68 years) from 2006‒2012.

Adherence was based on the number of prescriptions filled. Presence of depression was defined as at least one diagnosis code on at least one inpatient claim, or at least two outpatient claims during the study period.

Of the 31,033 beneficiaries meeting inclusion criteria, 20 percent were diagnosed with depression following COPD diagnosis. Average monthly adherence to COPD maintenance medications was low, peaking at 57 percent in the month following first fill, and decreasing to 25 percent within 6 months.

This is the first study to look at how depression affects adherence to COPD treatment, the researchers said of their study, which appears in Annals of the American Thoracic Society.