Chronic Stress May Age the Immune System, Study Finds

Chronic stress does more than disrupt sleep or mood — it may actually accelerate aging in the immune system, according to new research.Scientists traced a biological chain reaction running from specific brain regions through the gut and into the bone marrow of mice, where blood stem cells showed signs of premature aging under prolonged stress.Researchers at Sun Yat-sen University at Guangzhou, Guangdong, in China studied multiple mouse models exposed to different types of psychological stress, from chronic pain to repeated mild stressors, according to a study published in Cell Stem Cell, a highly ranked journal for scientific research.In every case, blood stem cells declined in number, died at higher rates, and shifted toward producing inflammatory cells rather than lymphoid immune cells — the type needed to recognize infections and mount targeted responses. This is the same pattern observed in naturally aging animals, leading researchers to conclude that stress may be pushing these cells toward old age before their time.To confirm the damage was cellular and not circumstantial, the team transplanted blood stem cells from stressed mice into healthy ones. The cells continued to underperform, unable to rebuild a healthy immune system, suggesting the damage was encoded in the cells themselves.Using neural mapping techniques, researchers identified two brain regions that went quiet under stress: the medial prefrontal cortex, which is involved in self-reflection, social cognition, emotion regulation, decision-making, and memory; and the periaqueductal gray, which is a gray matter hub in the center of the brain responsible for regulating pain modulation and defensive behavior. Suppressing either region produced the same bone marrow damage. Reactivating them in stressed mice allowed the cells to recover.These brain regions were connected to sympathetic nerve pathways that influence the small intestine. When researchers surgically severed that nerve connection, the bone marrow effects disappeared entirely.The gut itself also changed under stress. Levels of a gut bacteria strain that produces a molecule called spermidine, which is involved in cellular maintenance, dropped significantly. Without adequate spermidine, blood stem cells lost their internal recycling system, allowing toxic byproducts to accumulate and trigger cell death. Supplementing stressed mice with spermidine or replenishing the bacteria strain, known as Lactobacillus reuteri, restored stem cell function and improved immune response.The researchers note the study’s limitations, saying that all experiments were conducted in mice, and they do not know if the same pathway operates in humans, even though virtually all prior animal studies have resulted in the same outcomes for humans. The researchers also said a system used to track movements, changes, and distributions of molecules in biological systems called isotope-labeled tracing is still needed to confirm that bacteria-associated spermidine physically reaches bone marrow and acts directly on stem cells.

Chronic Stress May Age the Immune System, Study Finds

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