What hibernating bears can teach us about human health
Photo by Ali Jafarov on Unsplash
After a bout of illness, even the stairs can feel harder than they did before. Prolonged inactivity weakens our muscles, making the bear's winter routine an intriguing puzzle: how does an animal retain so much strength after months without exercise or meals?
The answer is emerging from studies that follow bears through the seasons, comparing their blood and muscle in winter with samples taken when they are active. Together, the findings show how the animals conserve fuel while protecting the tissues they will need when they emerge.
What happens to a bear’s body during hibernation
Hibernation is a regulated physiological state in which bears reduce their energy requirements and draw on fat accumulated before winter.
A study published in Science in 2011 found that hibernating black bears reduced their metabolism to around a quarter of its basal rate (the energy expenditure needed to sustain basic bodily functions at rest) while their body temperature cycled between approximately 30°C and 36°C. Their substantial energy savings therefore went well beyond what cooling alone could explain.
Bears achieve these savings while remaining much warmer than small hibernating mammals that cool close to freezing. Using less energy helps stored fat last through winter, while preserving muscle allows the animal to find food when it emerges.
How bears preserve muscle during hibernation
Human muscle is continually renewed through the production and breakdown of proteins. During prolonged inactivity, that balance can shift towards muscle loss, while fasting adds pressure to use the body's own resources.
Bears limit muscle loss while also reducing the energy their muscles use. One clue comes from myosin, a motor protein involved in contraction that consumes adenosine triphosphate, or ATP, the molecule cells use to supply energy.
In a 2025 Nature Communications study, researchers compared muscle fibres sampled from brown bears during summer and hibernation. Winter samples showed a modest decline in force production alongside a pronounced reduction in ATP-consuming activity. This helps explain how bears stretch their energy reserves: even their resting muscle machinery becomes more economical.
To investigate muscle preservation itself, scientists have also examined signals travelling through the bloodstream. In a 2018 study published in Scientific Reports, researchers exposed human muscle cells grown in the laboratory to serum collected from bears in winter and summer. Serum is the liquid remaining after blood has clotted.
Compared with summer serum, winter serum reduced protein breakdown and increased the cells' protein content. The experiment showed that circulating substances associated with hibernation could influence protein maintenance in human cells.
Identifying those substances and understanding their effects could inform research into muscle wasting during ageing, illness and immobilisation.
How hibernating bears protect against blood clots
Muscle loss is only one consequence of inactivity. In people, becoming immobilised can also increase the risk of venous thrombosis, where clots form inside veins. A clot that travels to the lungs can become life-threatening.
An international team led by researchers at LMU University Hospital Munich investigated how hibernating brown bears protect themselves against this danger. Their work, published in Science in 2023, involved trips to central Sweden in winter and summer. They located bears using GPS transmitters and collected blood while the animals were sedated, allowing them to compare the two seasons. Some tests took place in a mobile laboratory; samples were also taken to Munich for closer examination of platelets, the blood components involved in clotting.
One protein stood out: heat shock protein 47, or HSP47. Its abundance in bear platelets fell to roughly one fifty-fifth of the summer level during hibernation.
The team connected reduced HSP47 with less interaction between platelets and inflammatory cells, helping suppress processes that promote clot formation.
The investigation also identified related changes in people with long-term spinal cord injuries and healthy volunteers who spent three weeks in bed.
These findings revealed a protective response to prolonged immobility shared across species. They also identified HSP47 as a potential target for medicines to prevent dangerous clotting, particularly when patients suddenly become immobilised.
Reversible insulin resistance in hibernating bears
Alongside these adaptations to inactivity, bears change how they manage stored fuel. Part of that adjustment involves insulin, the hormone that helps regulate blood glucose.
In humans, insulin resistance means cells respond less effectively to that signal and is an important feature of type 2 diabetes. Bears undergo a seasonal form of insulin resistance during hibernation, then regain sensitivity during their active season.
At Washington State University's Bear Research, Education and Conservation Center, scientists investigated this reversibility using grizzly-bear blood serum and cultured bear fat cells.
Their 2022 study in iScience showed that the serum's season of origin influenced patterns of gene activity in the cells. Analysis identified eight circulating proteins associated with seasonal changes in insulin sensitivity.
Those proteins provide specific leads for investigating how bears move between insulin-resistant and insulin-sensitive states. Understanding that reversibility could offer insights into the persistent insulin resistance involved in human metabolic disease.
What hibernation reveals about tau and Alzheimer’s disease
Reversible changes during hibernation also interest scientists studying the nervous system. One focus is tau, a protein that binds to microtubules, structures within nerve cells. In Alzheimer's disease, abnormally modified tau accumulates in tangles.
A 2025 study measured tau markers in brown-bear blood and examined brain tissue from golden Syrian hamsters. During hibernation, both showed increases in certain forms of tau carrying phosphate groups; these are chemical modifications also investigated in Alzheimer's research.
The hamster brain samples, however, did not show increased levels of tau fragments associated with tangle formation. The researchers described hibernation as a model for studying how these chemical changes can occur reversibly without the aggregation associated with disease.
Together, these studies give new meaning to the familiar sight of a bear emerging in spring. Its ability to walk through its territory and search for food follows months of regulated energy use, muscle maintenance and changes in blood chemistry. By identifying the mechanisms behind that winter survival, scientists are gaining concrete leads for understanding how human bodies might better withstand illness and prolonged inactivity.
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