Major Depression Linked to Insulin Resistance- JAMA Study
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Individuals experiencing a current episode of major depressive disorder (MDD) are significantly more likely to have insulin resistance (IR), new research shows.

Investigators found patients with MDD were 51% more likely to have IR compared with their counterparts without the depressive disorder. In addition, in individuals experiencing current depression, IR was also associated with depression severity and depression chronicity.

For the study, the researchers drew on data from the Netherlands Study of Depression and Anxiety, a longitudinal Dutch study of adults that "describes the course and consequences of depressive and anxiety disorders."

The study included 1269 study participants with current MDD (n = 536), remitted MDD (n = 394), and control participants without a history of MDD (n = 339).

In addition to investigating the association between MDD and IR, the researchers also wanted to understand "whether using different surrogate IR measures has consistent association with MDD."

IR was determined using two surrogate markers — the quantitative insulin sensitivity check index (QUICKI) and the triglyceride to high-density lipoprotein (HDL) ratio.

Participants in the bottom quartile of the QUICKI were categorized as IR, while all other participants were categorized as being "insulin sensitive."

The second surrogate IR measure — the triglyceride-HDL ratio — is an index based on fasting blood sample measurements, in which the determination of IR was based on sex-specific cut points.

Depression was determined based on the Composite International Diagnostic Interview, while depression severity was based on the Inventory of Depression Symptomatology. "Chronicity" was defined as depression during the preceding 4 years and was measured using the life chart review.

Insulin resistance was associated with current, but not with remitted, MDD. In a model adjusted for age, sex, education, partner status, smoking status, and alcohol consumption, IR, as assessed by both measures, was linked to depression severity — but only the triglyceride-HDL ratio yielded an association between IR and depression chronicity.

IR was not associated with depression severity or chronicity in remitted MDD on either measure. The findings — specifically the association between current, but not remitted, MDD — suggest that "IR is a state, rather than a trait, biomarker of depression," the authors note.

"There are many plausible mechanisms between IR and MDD," said author. "Some hypotheses for the link include inflammations, alterations to the hypothalamic-pituitary-adrenal axis, and changes in health behavior.

"We learned two things from this study — first, that insulin resistance was associated with being in a depressive episode and with the severity of that episode," said study authors. "Second, we learned that we can estimate insulin resistance using a surrogate measure that is clinically accessible — the triglyceride/HDL ratio."