A large-scale Danish study strengthens the hypothesis that mood disorders like depression are directly tied to inflammation.

Depression and other mood disorders could be the brain’s response to inflammation, according to a new nationwide study from Denmark released Wednesday.

The study, published in the journal JAMA Psychiatry, is the largest of its kind and adds further evidence to the emerging theory that certain mental health conditions could be caused by inflammation.

Researchers found that patients with an autoimmune disease were 45 percent more likely to have a mood disorder, while any history of infection increased the risk of a mood disorder by 62 percent. About one-third of people diagnosed with a mood disorder had been hospitalized in the past for a serious infection.

Inflammation is the body’s protective response to an infection, while autoimmune disorders are inflammatory conditions caused by the body’s overreaction to naturally occurring substances and tissues.

“The associations found in this study suggest that autoimmune diseases and infections are important…factors in the development of mood disorders in subgroups of the patients possibly because of the effects of inflammatory activity,” the researchers wrote.

The new study offers insight into the mechanism of common mood disorders, including depression and bipolar disorder, and may help guide treatment and prevention efforts.

The Danish researchers drew on a nationwide database of more than 3.56 million people born between 1945 and 1996. Of those people, about three percent—91,637 people—were admitted to a free state hospital for mood disorder treatment.

Researchers compared the incidence of infections like sepsis, hepatitis, and urinary tract infections, as well as autoimmune disorders like lupus, anemia, Celiac disease, and Crohn’s disease, with the incidence of bipolar disorder, depression, psychotic depression, and other mood disorders.

They found a strong correlation between infection, autoimmune disorders, and mood disorders, strengthening the hypothesis that depression is directly linked to inflammation.

Earlier this year, another team of Danish researchers published a study in JAMA Psychiatry showing that elevated levels of a C-reactive protein—which the body produces in response to inflammation—in the blood are associated with an “increased risk for psychological distress and depression in the general population.”

In 2011, a study in the Journal of Neuroinflammation found that high levels of another byproduct of inflammation, quinolinic acid, are associated with chronic depression and suicidal tendencies.

These discoveries may point us toward better treatments for chronic mental health conditions.

“Anti-inflammatory agents have actually been suggested to improve mood symptoms in patients with inflammatory disorders and enhance responsiveness to antidepressants,” the latest study reported.

Getting regular cardiovascular exercise, drinking plenty of water, and relieving stress are all proven ways to help reduce inflammation.

A diet rich in omega-3 fatty acids like olive oil and salmon, dark leafy greens, ginger, garlic, and green tea has also been shown to reduce inflammation and improve overall health. For more information, see the links below.