Inflammation may help explain depression, diabetes link

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.