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Chronic kidney disease, which can lead to kidney failure, is a progressive loss of kidney function over months or years. Diabetes is the most common cause of kidney failure, according to the U.S. National Institute of Diabetes, Digestive and Kidney Diseases.
Working with diabetic patients with chronic kidney disease, study author Dr. Margaret Yu, a nephrology fellow at the University of Washington in Seattle, found that many also suffered from depression. She wondered whether the kidney problems were causing depression, or if depression somehow contributed to kidney disease.
For the study to be published in the Clinical Journal of the American Society of Nephrology, the researchers looked at almost 4,000 adults with diabetes who were patients in a large health maintenance organization in Washington state.
The researchers also looked at laboratory tests of kidney function, and at patients' responses to a questionnaire used to determine whether they were depressed.
About 12 percent had signs of major depression, and about 9 percent had minor depressive symptoms. Throughout the study period of almost nine years, about 2 percent of participants developed kidney failure.
Because many of the symptoms of depression are similar to the signs of advanced kidney disease -- such as low energy, reduced appetite, difficulty sleeping and lack of interest in activities -- the connection between depression and kidney disease was most notable among the patients with major depression, Yu said.
The researchers also found that how well patients took care of themselves did not seem to have as great an impact on the risk of kidney disease as did depression.
What could be the connection between depression and kidney disease? "There is an association right now but we don't know what the mechanisms are," said Dr. Martin Zand, a professor of medicine and medical humanities at the University of Rochester Medical Center in Rochester, N.Y.
"But these findings are very consistent with a lot of studies in other areas that show depression affects cardiovascular health, medication adherence, inflammatory markers and stress hormones, all things which have been shown to affect kidney disease," said Zand, who was not associated with the study.
Zand said he thinks the impact of depression is both physiological and psychological.
"What I mean by that is that many of the things that someone with diabetes needs to do to maintain their health requires some engagement and motivation: checking blood sugar five times a day, watching your diet and exercise, getting checkups regularly, getting lab work done," he said. "When you're depressed, you tend not to do those things."
Study author Yu agreed. "We still don't understand the mechanism for depression's impact on the progress of the disease," she said. "But it's not just behavioral; it's something else."
The study had limitations. Zand noted that the level of self-care was only addressed at the beginning of the study. "But the more depressed you are, the less you may do, and more complications may arise," he said. "The more bad news you get, you may develop a sense of helplessness."
The researchers note that they could only identify an association -- not a cause-and-effect relationship -- between major depressive symptoms and kidney failure. Additional studies will be needed to determine whether routine screening and treatment of depression in diabetics can reduce the risk of kidney disease, they noted.
Yet the findings suggest that people with diabetes would benefit from routine screening for depression, Yu said. "We need to raise awareness among health care providers about the magnitude of this problem," she said. "Many suspect this but have not recognized it completely. Our patients are at high risk for depression and can have poor outcomes as a result."
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