Inflammation is not always linked to depression, study finds

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Multiple prior studies have found higher levels of inflammation in older individuals with depression.

In a study from Penn Medicine, scientists found that clinically depressed older people, on average, don’t have elevated levels of inflammation if they don’t already have other inflammatory conditions such as arthritis.

The new study suggests that depression occurs independently of inflammation for many older adults.

Furthermore, depression-inflammation links are due to the greater incidence of inflammatory conditions, which in general are common in older people.

National surveys in the United States suggest that, although depression is diagnosed more often among younger adults, about five percent of people who are at least 50 years old have had a major depressive episode in the past year.

Researchers suspect that many of these cases of late-life depression are caused by inflammation—in part because studies have found higher levels of inflammatory immune proteins in the blood of older people with depression, compared to non-depressed people of the same age.

Prior research also has shown that levels of inflammation markers generally tend to rise with increased age, as chronic illnesses set in and the body’s immune-regulating systems weaken.

In the current study, the team found that the link between depression and inflammation is not as clear-cut as the prior literature suggests.

They used online and in-person screening of over 1,100 depressed individuals to recruit a group of 63 individuals, aged 50 to 80, who met the criteria for the major depressive disorder but did not have other inflammatory conditions.

Comparing this group to 29 healthy individuals of the same age, even with highly sensitive measurements, the researchers found no big differences in bloodstream levels of 29 different inflammation-linked immune proteins.

The researchers then randomized 60 of the depressed patients to receive either a standard antidepressant drug, or the antidepressant plus an anti-inflammatory drug, or placebo, for eight weeks.

They found that while the two antidepressant-treated groups showed strong improvement in their depression ratings relative to placebo, there was no difference in outcome between the antidepressant and the antidepressant-plus-anti-inflammatory group.

Moreover, in all three groups, the subjects’ blood levels of inflammatory markers were low before treatment and did not drop strongly as a result of treatment.

The researchers even tested the cerebrospinal fluid for the levels of the inflammatory protein IL-1β, and again found low levels both before and after treatment.

The study, therefore, suggests that, in many older adults, depression occurs independently of inflammation, and probably won’t be alleviated by anti-inflammatory treatments unless inflammation is present in addition to depression.

If you care about depression, please read studies about how ketamine prevents depression, and dual treatments to fight PTSD and depression.

For more information about mental health, please see recent studies about depression drug that may come with a higher death risk, and results showing eating fruit more often may reduce depression.

The study was conducted by Yvette Sheline et al and published in Nature Translational Psychiatry.

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