People with both depression and diabetes have higher markers of inflammation in their blood than those with diabetes alone, a new study suggests.

Researchers have known that people with diabetes have a higher rate of depression than those without the blood sugar disorder. And people with both conditions tend to do worse over the long run than people with diabetes but no depression.

Inflammation is a sign of the body responding to disease, trauma or other stressors. The new study suggests higher inflammation levels may help explain the link between diabetes, depression and worse overall health, researchers said. But it’s still not clear how, exactly.

“We asked, why is depression so bad for diabetes? The study suggests that we have a possible biological explanation,” Dr. Khalida Ismail told Reuters Health.

“Inflammation may be driving a number of different long-term conditions. That’s quite a new way of thinking of the mind and the body,” she said.

Ismail worked on the study at the Institute of Psychiatry at King’s College London in the UK.

She and her colleagues examined 1,227 people with newly diagnosed type 2 diabetes.

Those who reported symptoms of depression tended to be younger and heavier. They also had higher rates of heart and circulation problems and higher concentrations of established markers of inflammation in their blood, according to results published in Diabetes Care.

After the researchers took into account other potential differences between study participants, such as their age, sex, amount of body fat and use of certain medications, six of the 12 inflammatory markers they measured were still linked to depression.

More than one in 20 Americans reported depression in 2005-2006, and about one in 12 has diabetes, a major cause of heart disease and stroke, according to the Centers for Disease Control and Prevention.

Death rates are up to twice as high among people with depression and diabetes as those with diabetes alone, Ismail said.

“The conventional wisdom is that this is a consequence of the psychological burden of having diabetes,” she said. “If that’s the case, if you treat the depression, the diabetes control should improve.”

But it does not, Ismail said. So she began to wonder if inflammation, often seen in people with diabetes, could help explain both conditions and the worse outcomes.

“It’s a bit like an engine,” Ismail said. “You’re running a bit higher. So there’s this constant low-grade inflammation and that’s causing damage to your brain, your pancreas and to your vascular system.”

Dr. Anne Peters said she often sees patients with diabetes, depression and elevated markers for inflammation. But there are still many questions about how they are related.

“The development of depression could in part be triggered by inflammation, but we don’t know what comes first,” she told Reuters Health. “This paper can’t prove causality. The interplay is so complicated.”

Peters directs the University of Southern California Clinical Diabetes Program in Beverly Hills and was not involved in the current study.

“To me, it’s as much a part of diabetes care as looking at blood sugars to screen for and treat depression,” she said.

She believes the best way to begin to combat both depression and diabetes is to eat well and exercise. Her own study found that depression scores among people with diabetes dropped when they were physically active.

“If you exercise, you feel better, your inflammatory markers improve. It’s all about lifestyle interplaying with your health. We’re just living lives we were not made to live. We sit still too much at work. We’re caged up in a way,” she said.

Peters cited a 2012 study that found that people taking antidepressants were at higher risk for diabetes than non-antidepressant users, even after taking their weight into account. The current study did not examine antidepressant use.

SOURCE: Diabetes Care, online May 19, 2014

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The Association Between Depressive Symptoms and Systemic Inflammation in People With Type 2 Diabetes: Findings From the South London Diabetes Study

OBJECTIVE The prevalence of depression and depressive symptoms is increased twofold in type 2 diabetes compared with the general population and is associated with worse biomedical outcomes and increased mortality. Type 2 diabetes, cardiovascular disease, and depression in nondiabetes subjects are independently associated with raised concentrations of circulating inflammatory markers, but it is not known if a similar association is observed in type 2 diabetes. We tested the hypothesis that higher depressive symptom scores in newly diagnosed type 2 diabetes patients were associated with higher concentrations of inflammatory markers.

RESEARCH DESIGN AND METHODS Depressive symptoms in adults with newly diagnosed type 2 diabetes recruited from primary care were assessed using the Patient Health Questionnaire-9. Twelve markers of inflammation (C-reactive protein [hs-CRP], interleukin-4 [IL-4], IL-6, IL-10, vascular endothelial growth factor [VEGF], tumor necrosis factor-α [TNF-α], IL-1β, IL-1 receptor antagonist [IL-1RA], monocyte chemotactic protein-1 [MCP-1], white blood cell count [WBC], adiponectin, and triglyceride [TG]) were measured. Covariates included sociodemographic factors, adiposity, macrovascular disease, glycated hemoglobin (HbA1c), and prescribed medication. The association between each inflammatory marker and depressive symptom score was estimated by multiple linear regression.

RESULTS The baseline cohort consisted of 1,790 participants. After adjusting for covariates, CRP (B = 0.13, P < 0.001), IL-1β (B = 0.06, P = 0.047), IL-1RA (B = 0.13, P < 0.001), MCP-1 (B = 0.11, P = 0.001), WBC (B = 0.13, P < 0.001), and TG (B = 0.10, P < 0.001) were associated with depressive symptoms.

CONCLUSIONS Increased inflammation may be involved in the pathogenesis of depressive symptoms in type 2 diabetes and contribute to the increased risk of complications and mortality in this group.

  Jean-Pierre S. Laake,
  Daniel Stahl,
  Stephanie A. Amiel,
  Frank Petrak,
  Roy A. Sherwood,
  John C. Pickup and
  Khalida Ismail