Tony Z. Tang, adjunct professor in the department of psychology at Northwestern University, said that participants who were taking medications for their conditions fared worse because their illnesses were more severe.
"None of these treatments are cures, unlike antibiotics for infections. So, depressed patients on antidepressants and diabetic patients on insulin still frequently suffer from their main symptoms," said Tang. "These patients fare worse in the long run because they were much worse than the other patients to start with."
Tang cautioned against drawing too many conclusions from the study. He noted that the correlations between diabetes and depression declined markedly when excessive weight and inactivity were controlled for in the study.
"This suggests that much of the observed correlation between depression and diabetes comes from confounding variables," he said. "In layman's terms, being fat and having an unhealthy lifestyle makes people more likely to be depressed, and [also] more likely to have diabetes."
But if research establishes a strong connection between the two illnesses it could advance treatment, Tang added.
"If a substantial causal connection is established between the two disorders, it would be rather novel and it could potentially change how we understand and treat both disorders," Tang said.
Dr. Joel Zonszein, director of the Clinical Diabetes Center at Montefiore Medical Center in New York City, said establishing causal relationships is difficult in a study based on questionnaires because self-reports can be inaccurate.
"This is not ideal," he said. "It's difficult to say what is causing what, if one is causing the other. This is very difficult to elucidate."
A large, controlled, randomized study is needed, said Zonszein, who is also a professor of clinical medicine at Albert Einstein College of Medicine, in New York City
All rights reserved