But he praised the research, noting that tracking such as large number of subjects "over a long period of time" strengthened the findings.
Hu, also a professor of medicine at Harvard University, said the study conclusions were valid. When two conditions share the same risk factors (obesity and lack of exercise), "we can still say that the conditions are linked and one is both the cause and consequence of the other condition," he explained.
Depression can affect blood sugar levels and insulin metabolism through increased cortisol, contributing to unhealthy eating habits, weight gain and diabetes, he said.
"On the other hand, management of diabetes can cause chronic stress and strain, which in the long run, may increase risk of depression," said Hu. The two "are linked not only behaviorally, but biologically."
For more on diabetes, go to U.S. National Library of Medicine .
SOURCES: Joel Zonszein, M.D., professor, clinical medicine, Albert Einstein College of Medicine, and director, Clinical Diabetes Center, Montefiore Medical Center, New York City; Frank B. Hu, M.D., Ph.D., professor, nutrition and epidemiology, Harvard School of Public Health, professor, medicine, Harvard Medical School, Boston; Tony Z. Tang, Ph.D., adjunct professor, department of psychology, Northwestern University; vice chairman, WorldLink Foundation; Nov. 22, 2010, Archives of Internal Medicine
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