Women with major depressive disorder had abnormally elevated biomarkers for immunity in both sweat and plasma, even when they no longer had symptoms of depression, according to a new study. The findings, which could explain why women with major depression are at increased risk of other medical illnesses, will be presented Saturday, June 2, at The Endocrine Society’s 89th Annual Meeting in Toronto.

The researchers, from the U.S. National Institutes of Health, found the elevated levels in blood (the typical way to measure the biomarkers) and in sweat, which one of the investigators said was innovative. Study participants wore patches for 24 hours during regular activities to collect their sweat for analysis. According to Dr. Esther Sternberg, a researcher at the National Institute of Mental Health (NIMH) and a study author, the scientists then used a highly sensitive new technology, called RIC (for recycling immunaffinity chromatography), developed by co-author Terry Phillips, immunochemist at NIH, to measure minute amounts of biomarkers in biological fluids. RIC allows measurement of multiple biomarkers in small amounts of fluids. The biomarkers analyzed were neuropeptides—stress-response substances—and cytokines—inflammation-inducing immune substances. Results of past studies have been inconsistent regarding whether cytokines and neuropeptides are elevated in the blood of people with major depressive disorder, Sternberg said.

The current study included 19 premenopausal women with a diagnosis of major depressive disorder, most of whom were no longer experiencing depression symptoms, as well as 17 healthy women with no history of depression. The study participants were part of the P.O.W.E.R. Study (Premenopause, Osteopenia/Osteoporosis, Women, Alendronate, Depression), a large study of bone turnover in women with major depressive disorder and in healthy controls, conducted by co-author Dr. Giovanni Cizza, endocrinologist at the National Institute of Diabetes and Digestive and Kidney Diseases.

Cytokines and some neuropeptides were strikingly elevated in the sweat of women with major depression, even in women who were in remission from depression. Measurements of all biomarkers in sweat were very similar to the same measurements in blood, showing that the noninvasive sweat test was as accurate as blood tests in these subjects, according to Sternberg.

“This finding fits with the known increased risk that women with major depressive disorder have for other diseases, in which inflammation and the stress-response systems play a role,” she said. Examples include osteoporosis, diabetes, and heart disease.

Sternberg added that it is noteworthy that the women in the study were premenopausal, since cytokine levels increase after menopause in nondepressed women.

The National Institutes of Health funded the study. Other study authors included Dr. Andrea Horvath Marques, NIMH fellow; Dr. Giovanni Cizza, endocrinologist at the National Institute of Diabetes and Digestive and Kidney Diseases; and Dr. Terry Phillips, NIH immunochemist.

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