Every second of every day, your body is quietly making millions of new blood cells deep inside your bones.
This happens in the soft tissue called bone marrow, which acts like a busy factory that never stops working. It produces red blood cells that carry oxygen, white blood cells that fight infections, and platelets that help stop bleeding.
This amazing system depends on a careful balance. Blood-forming stem cells create new cells, nearby support cells help them survive and grow, and immune signals keep everything working smoothly.
As people get older, this balance slowly becomes harder to maintain. Years of natural aging, low-level inflammation, and small genetic changes that build up over time can affect how the bone marrow works.
Sometimes a blood stem cell develops a mutation and begins producing more copies of itself than normal. This condition is called clonal hematopoiesis of indeterminate potential, or CHIP.
Most people with CHIP feel completely healthy and do not know they have it. However, it is surprisingly common. Around one in five adults over 60 years old has CHIP, and the number rises to nearly one in three people over 80.
Although there are no obvious symptoms, people with CHIP have a higher chance of developing blood cancer, heart disease, and other serious health problems.
Another disease linked to these abnormal blood stem cells is myelodysplastic syndrome (MDS). In MDS, the bone marrow can no longer make enough healthy blood cells.
People may become tired, develop frequent infections, or bruise and bleed more easily. About 30% of patients with MDS later develop acute myeloid leukemia, a fast-growing type of blood cancer.
For many years, scientists mainly believed that these diseases were caused by mutations inside blood stem cells. However, researchers have increasingly wondered whether the surrounding bone marrow environment also plays an important role.
To answer this question, an international team led by Judith Zaugg from EMBL and the University of Basel, together with Borhane Guezguez from the University Medical Center Mainz, carefully studied bone marrow samples from healthy volunteers and patients with MDS. The samples came from a large German research project on blood health in older adults.
The scientists used advanced laboratory methods to study individual cells, examine which genes were active, measure proteins, and identify where different cells were located inside the bone marrow. This allowed them to build one of the most detailed maps ever created of the bone marrow environment.
The researchers discovered that important changes happen before obvious disease appears. Healthy support cells that normally protect blood-forming stem cells gradually disappeared and were replaced by new support cells that produced large amounts of inflammatory substances.
These cells also attracted immune cells, especially certain T cells, creating an ongoing cycle of inflammation.
This unhealthy environment damaged the normal production of blood cells and changed the structure of the bone marrow itself. The altered environment made it easier for mutated stem cells to survive, grow, and eventually dominate the bone marrow.
One surprising finding was that the mutated blood cells did not appear to be the main cause of the inflammation. Instead, the surrounding bone marrow environment seemed to become unhealthy first, creating conditions that encouraged disease to develop.
The researchers also found that important signals that normally keep blood stem cells healthy inside the bone marrow became weaker in people with MDS. Without these signals, the body’s normal blood-making system gradually failed.
These findings also support the idea of “inflammaging,” the slow, long-lasting inflammation that often develops during aging and has been linked with cancer, heart disease, diabetes, and many other age-related illnesses. The study suggests that bone marrow is not simply affected by this inflammation but may also help drive it.
The discovery changes how scientists think about blood diseases. Instead of focusing only on abnormal blood stem cells, future treatments may also target the bone marrow environment itself. Reducing inflammation or repairing damaged support cells could slow or even prevent the progression from CHIP to MDS and leukemia.
The work also highlights that many important changes inside the body happen silently for years before symptoms appear. By detecting these hidden changes earlier, doctors may eventually identify people at high risk and begin treatment before serious disease develops.
The study was published in Nature Communications and provides important new insights into how aging changes the bone marrow and increases the risk of blood disorders. It may help guide the development of better ways to prevent and treat these diseases in the future.
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