The clinical trial, involving 160 participants with an average age of 66, found that those with insomnia experienced a threefold increase in depressed mood and symptoms after being exposed to an inflammatory challenge compared to their well-rested peers.
Their low mood lingered for more than six hours, while in those without insomnia, the effects were temporary.
The link between sleep and depression
Clinicians say the study highlights an important connection that has long puzzled mental health experts.
“It’s often like a chicken-and-egg situation — does insomnia cause depression or is insomnia a symptom of depression? The two are closely linked,” said Dr Rajiv Mehta, senior consultant psychiatrist at Sir Ganga Ram Hospital.
“Insomnia is usually part of the depressive spectrum and people with insomnia are much more vulnerable to negative thinking, which stresses the brain,” Dr Mehta explained. Stress on the brain, he added, can spill over to other body systems and make them vulnerable too.To test the relationship, researchers administered a small dose of endotoxin — a substance that safely triggers temporary inflammation — to half the participants, while the rest received a placebo. Mood changes were then measured using self-reports and clinical assessments.Inflammation is the body’s natural defence against infection or injury. But when heightened, it can disrupt brain chemistry and mood. Both groups in the trial showed similar biological signs of inflammation, such as elevated cytokines, yet only those with insomnia displayed a strong link between the immune response and worsening mood.
How inflammation affects the brain
Explaining the underlying science, Dr Pavitra Shankar, associate consultant in psychiatry at Aakash Healthcare, said cytokines — the immune system’s signalling proteins — can cross into the brain and alter communication between nerve cells.
“During inflammation, especially in what we call a cytokine storm, levels of IL-6 and TNF-surge. They disturb the brain systems responsible for serotonin and dopamine, the chemicals that regulate mood. For older adults with insomnia, this disruption is amplified, worsening depression and impairing emotional regulation,” she said.
The study’s authors concluded that older adults with insomnia carry a “hidden vulnerability” and should be closely monitored for depression during infections or illnesses, when inflammation is high.
What can help mitigate the risks
Experts also point to interventions that can improve sleep while reducing inflammation.
Dr Prashant Goyal, senior consultant in psychiatry at Sri Balaji Action Medical Institute, said: “Cognitive behavioural therapy for insomnia and mind-body practices like tai chi have been shown to improve sleep and reduce inflammatory markers. Exercise programmes, whether aerobic or resistance, also help lower inflammation and improve mood. This trial strengthens the case for combining sleep therapies with physical activity and stress reduction to prevent depression.”
With India’s ageing population set to double in the coming decades, psychiatrists warn that the overlap between insomnia, inflammation and depression will only grow more significant. Addressing sleep problems, they say, could be a key strategy in safeguarding mental health among seniors.
(With inputs from ToI)
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