Immune reactions linked to depression and anxiety may lead to better screening and treatment of both, according to an analysis presented Monday during the online European College of Neuropsychopharmacology Congress.
Researchers from the Netherlands Study of Anxiety and Depression linked inflammation to depression and higher levels of a type of cholesterol called C-reactive protein to anxiety. Discerning between the two, they said, may improve treatment.
In comparing blood test findings from adults with depression, anxiety, or both to those of healthy controls, the researchers observed that those with depression alone had elevated C-reactive protein, while those with anxiety alone did not.
C-reactive protein levels in blood are used to measure inflammation. C-reactive protein is made by the liver and released into the bloodstream in response to inflammation.
Adults with only depression alone also had higher levels of triglycerides in their blood than those with only anxiety, the data showed.
"Depressed people had high levels of triglycerides, but lower levels of omega-3-fatty acids," than people with anxiety, study co-author Hilde de Kluiver, a doctoral student in psychiatry at Amsterdam University Medical Center in the Netherlands, said in a statement.
"In contrast, those people who had anxiety disorder had a lipid composition very similar to the healthy control group," she said.
Historically, anxiety and depression have often been linked and considered to be closely related -- and many people suffer from both conditions simultaneously -- according to the Anxiety and Depression Association of America.
The two disorders share several symptoms -- including difficulty sleeping and concentrating -- and both can develop following traumatic life events or as a result of inherited, genetic characteristics, de Kluiver, and her colleagues said.
As many as half of those with major depressive disorder, a type of severe depression, have a history of anxiety, they said.
In recent years, depression has been associated with disturbances in the body's immune system and metabolism, and earlier research has shown that depressed people tend to have different biochemical markers to those of healthy people, according to the researchers.
More than 40 million American adults have anxiety disorders, while 15 million have experienced at least one depressive episode in the past year, the Anxiety and Depression Association of America estimates.
For this analysis, de Kluiver and her colleagues collected blood samples from 304 people with depression, 548 with anxiety, 531 with both depression and anxiety, 807 with remitted disorders -- or periodic anxiety and depression -- and 634 otherwise healthy adults.
Using a nuclear magnetic resonance detector, they tested for associations between 40 metabolites found in blood and symptoms of depression and symptoms of anxiety.
In addition to the difference between people with the two disorders, the researchers found that metabolites like triglycerides that have been linked with depression were also linked with the severity of the depression -- meaning that those with more of these metabolites had more severe depression, de Kluiver said.
Based on the findings, it's possible that these metabolites can be used to screen people for disorders such as anxiety and depression and to serve as targets for drugs designed to treat them.
"Our group is now planning to test whether depressed people with altered inflammation might respond to treatment with anti-inflammatory drugs," de Kluiver said.