25 May The Immunology of Hibernation: What Animals Know About Winter That We Forgot
Winter marks a shift — in temperature, in light exposure, and in immune function. For most of human history, seasonal changes brought corresponding shifts in behaviour: reduced activity, earlier bedtimes, more nutrient-dense foods, and time spent indoors. But modern life overrides these cues, keeping us in a summer-like pace year-round — and the immune system pays the price.
Fatigue, increased susceptibility to viral infections, and inflammatory flares during the winter months are not just a consequence of “cold and flu season.” They can be a sign of mismatch: between the environment our physiology evolved for, and the one we now live in.
Emerging research into hibernation biology and neuroimmunology suggests that seasonal slowing — including rest, darkness, and reduced metabolic output — plays a central role in immune regulation. This article explores what the science of hibernation can teach us about supporting immune resilience during winter.
Winter Promotes a Shift Toward Immune Conservation
In colder seasons, the immune system adjusts its activity. This shift is partly driven by circadian and circannual rhythms — biological clocks influenced by light exposure, temperature, and behavioural inputs. Winter typically leads to:
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Increased melatonin secretion due to longer periods of darkness
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Reduced cortisol amplitude, affecting immune signalling
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A shift from pro-inflammatory innate immunity toward adaptive immune memory and tissue repair
In mammals, including humans, this adaptive response may help conserve energy while still maintaining core immune functions.
Hibernating Animals Provide a Model for Human Immunity in Winter
Hibernation isn’t a shutdown — it’s a strategic recalibration. In species like bears and ground squirrels, studies show a downregulation of inflammatory pathways (e.g., IL-1β, TNF-α) and a preservation of immune memory, such as B cell survival and T cell homeostasis, during hibernation periods.
This suggests that immunity is not suppressed, but rather selectively modulated. Pro-inflammatory processes that require high metabolic output are paused, while functions that support long-term immune surveillance are maintained.
In humans, chronic exposure to stressors (e.g., artificial light, high work demands, irregular sleep) during winter can interfere with this recalibration. Instead of entering a low-inflammation, restorative mode, the body remains in a sympathetic-dominant, cortisol-driven state, increasing susceptibility to viral infections and reducing mucosal immune defenses.
The Role of Sleep, Light, and Melatonin in Immune Function
One of the key links between seasonal change and immunity is melatonin. Beyond its role in sleep regulation, melatonin exerts immunomodulatory effects, including:
Longer nights in winter naturally increase melatonin secretion — if light exposure is well-regulated. However, exposure to artificial light at night suppresses melatonin, potentially impairing immune function. This is particularly relevant for mucosal immunity, as melatonin supports the secretion of secretory IgA, the first line of defence in the respiratory and gastrointestinal tracts.
Immunity and Energy Allocation: Why Rest Matters
The immune response is energy-intensive. Fever, cytokine production, and immune cell proliferation place significant demands on metabolic systems. In states of energy deficit or chronic stress, the body may deprioritize immune maintenance in favour of immediate survival.
In hibernation biology, this is reflected in metabolic downregulation and immune preservation. In humans, similar mechanisms are likely at play — though they depend on the presence of adequate rest and nutrient intake.
Chronic activation of the HPA axis (hypothalamic-pituitary-adrenal) and poor sleep quality have been associated with:
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Reduced natural killer (NK) cell activity
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Impaired B cell antibody production
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Increased systemic inflammatory markers such as CRP and IL-6
Supporting parasympathetic tone — through rest, nervous system regulation, and circadian rhythm alignment — can promote a shift away from this inflammatory state.
Clinical Implications for Naturopathic Support in Winter
Rather than focusing solely on immune stimulation, naturopathic care during winter can emphasise immune modulation and restoration. This aligns with the body’s seasonal needs and reduces the risk of inflammatory flares or burnout.
Key clinical strategies include:
1. Circadian Regulation
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Encourage morning light exposure within the first hour of waking
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Minimise blue light exposure after sunset (e.g., use amber filters or lighting)
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Prioritise consistent sleep-wake cycles
2. Mitochondrial and Immune Nutrient Support
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Vitamin D3 becomes deficient in many Australians during winter, so testing and supplementation may be necessary
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Eating foods high in Vitamin A, Zinc, and Omega-3 fatty acids to support mucosal barrier and immunity
3. Nervous System Modulation
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Adaptogens and medicinal mushrooms such as lion’s mane may help with nervous system modulation
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Vagal tone support through breathwork, gentle exercise, or hydrotherapy
4. Digestive Support for Mucosal Immunity
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Use warming, easily digested meals to reduce gut burden (e.g., soups, broths)
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Include prebiotic fibre foods such as apples, cabbage, and artichokes
Summary
The immune system is not designed to operate in a constant state of vigilance. Like all biological systems, it follows rhythms — and winter is a time for recalibration, restoration, and immune conservation. Hibernating mammals offer a compelling model: by slowing down, they preserve immune integrity while avoiding unnecessary inflammatory expenditure.
For humans, embracing seasonal rest and reducing overexertion can be a clinically meaningful strategy to reduce infection risk, manage autoimmune flares, and support long-term immune balance.
Your immune system is listening to your environment. In winter, give it the quiet it needs to do its best work.
