Impaired sleep quality may help explain long-term effects of depressive symptoms on inflammation

New research published in PLoS One showed that depressive symptoms were longitudinally associated with increased inflammation. In addition, the new study provides evidence that sleep quality plays an important role in the link between depressive symptoms and later inflammation.

“From my personal experience with mild depressive symptoms, I became interested in the long-term health effects of depressive symptoms,” explained study author Sunmi Song, a research professor at Korea University’s Department of Health Sciences. Felt like I lost my usual high energy and motivation. I wondered how long this lingering effect might last, luckily I had the opportunity to study this using data from the Middle Ages in the United States (MIDUS) cohort, and I colleagues in which studied the effect of depressive symptoms on inflammation throughout the body over an 11-year follow-up.”

The MIDUS study assessed depressive symptoms in 7,108 middle-aged adults in 1995. Eleven years later, 968 of those participants spent the night at the research center. In the morning, they completed a sleep quality assessment and provided fasting blood samples for measuring interleukin-6 (IL-6) and C-reactive protein (CRP).

IL-6 and CRP are inflammatory biomarkers associated with various inflammatory diseases. IL-6 is a cytokine that is produced by various cell types, including monocytes, macrophages, and T cells. CRP is a protein produced in the liver in response to inflammation. Both IL-6 and CRP are involved in the inflammatory response and have been implicated in diseases such as arthritis, inflammatory bowel disease, and psoriasis.

The researchers found that the more severe the depressive symptoms, the higher the levels of CRP in both men and women, and the higher the levels of IL-6 in women (but men). “In the current sample, for the main effect of depressive symptoms on CRP, each additional depressive symptom was associated with a 1.25 mg/L increase in CRP levels in men and women and a 1.40 pg/mL increase in IL-6 levels in women,” the authors explained. “This suggests that even mild depressive symptoms may be associated with higher systemic inflammation ten years later.”

The findings held even after controlling for concurrent depressive symptoms, age, socioeconomic status, ethnicity, BMI, smoking, chronic health conditions and drug use.

“The findings suggest that depressive symptoms in you or a loved one may require a long-term care plan to promote physical and mental health. In other words, seeking psychiatric treatment for acute depressive symptoms may not be enough to allow you to fully recover,” Song Tell PsyPost.

In addition, the researchers found evidence that subjective sleep quality mediates the association between depressive symptoms and CRP. Worsening of depressive symptoms in 1995 was associated with poorer overall sleep quality during clinical hospitalization, which in turn was associated with higher CRP levels in both men and women.

“Our study also suggests that monitoring your sleep quality may be particularly helpful in noticing the lingering deleterious effects of prior depression on the body, as sleep quality explains the longitudinal association between depressive symptoms and inflammation,” Song explained.

“I’ve personally found that making physical activity and expressive writing part of my daily routine helps maintain a good night’s sleep and full recovery from depressive symptoms,” explains Song. “(There are strong research findings supporting the efficacy of both approaches for depressive symptoms and clinical depression.) If you want to learn more about how to do expressive writing, I recommend a book, Expressive Writing: Words of Healing. ‘ by James Pennebeck and John Evan.”

The findings are in line with a 2020 meta-analysis of 107 cross-sectional studies that found that inflammatory markers tended to be elevated in people with depression. But like any study, the new study has some limitations.

“The main caveat of the findings is that those with depressive symptoms may show elevated inflammation 11 years later because they had elevated inflammation in the first place,” Song said. “The MIDUS study did not measure inflammation levels at baseline (at the start of the study), but only after 11 years.”

“Inflammation in the body is known to be associated with current depressive symptoms. Although we tried to account for this by controlling for those with inflammatory chronic diseases such as cardiovascular disease and arthritis at baseline and depressive symptoms at the time of the inflammation assessment, there is still a need for Future studies to verify the long-term lingering effects of mild depression. Symptoms persisted after controlling for baseline levels of inflammation.”

“I would like to add that depressive symptoms are often triggered by very difficult and painful life events, such as the loss of a loved one, a major failure in life goals, or unresolved social conflicts with significant others,” Song said. “We should allow ourselves or a loved one with depression sufficient time and resources to heal and grow.”

“My research shows that the healing process may take longer than people usually expect. I hope that people who are currently or have a history of depression use this as an opportunity to digest the personal meaning of pain and suffering in their lives, and to be healthier I want to express a lot of love and compassion to those who suffer from the lingering negative effects of depression.”

The study, “Longitudinal Associations between Depressive Symptoms and Inflammation: Mediators of Sleep Quality,” was led by Sunmi Song, Natasha N. DeMeo, David M. Almeida, Marzieh Majd, Christopher G. Engeland, and Jennifer E. Graham-Engeland write.

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