Many people feel tired when exposed to cold. This isn’t just anecdotal; it’s rooted in the body’s complex physiological responses to maintain its internal temperature. There is a scientific basis for why cold can cause fatigue, involving significant energy demands and impacts on sleep and mood.
How the Body Maintains Warmth
The human body possesses sophisticated mechanisms to regulate its core temperature, a process known as thermoregulation, ensuring it remains around 98.6°F (37°C) even when external temperatures drop. One immediate response to cold is vasoconstriction, where blood vessels near the skin’s surface narrow, reducing blood flow to the extremities. This action minimizes heat loss from the body’s surface, redirecting warmer blood to the core organs.
If vasoconstriction is insufficient, the body initiates shivering, an involuntary rhythmic contraction and relaxation of muscles. This muscular activity generates heat as a byproduct of increased metabolic activity. Beyond shivering, the body also uses non-shivering thermogenesis, primarily involving the activation of brown adipose tissue, or brown fat. Brown fat contains numerous mitochondria that burn calories to produce heat directly, rather than storing energy.
Energy Demands of Cold Exposure
Maintaining warmth in cold conditions requires substantial energy. Shivering is a highly energy-intensive activity, as muscles continuously work to generate heat. The body prioritizes core temperature, diverting significant energy to these thermoregulatory functions.
This increased metabolic demand depletes energy reserves, leading to fatigue. The body burns more calories to fuel warming mechanisms, similar to strenuous physical activity. This continuous effort to counteract cold can leave a person feeling drained and exhausted. Less energy remains for other functions, as the body’s resources are heavily invested in temperature regulation. This energy allocation is a survival mechanism, ensuring vital organs remain at an optimal temperature.
Cold’s Influence on Sleep and Mood
Beyond direct energy expenditure, cold conditions can indirectly contribute to feelings of tiredness by disrupting sleep quality. An excessively cold sleeping environment can make it difficult to fall asleep and maintain continuous sleep throughout the night. The body may struggle to reach the optimal temperature for sleep initiation, leading to prolonged wakefulness.
Fragmented or poor-quality sleep, often a result of discomfort in cold surroundings, can manifest as daytime fatigue and reduced alertness. Individuals might wake up feeling unrested, even after spending sufficient time in bed. This sleep disruption directly impacts daily energy levels and cognitive function.
Cold weather can also influence mood and energy levels through reduced exposure to natural sunlight. Shorter daylight hours and increased cloud cover during colder months limit the body’s exposure to light, which can affect the production of certain neurotransmitters. This can contribute to feelings of lethargy and a decrease in overall energy.
When Tiredness Indicates a Health Risk
While feeling tired in the cold is often a normal physiological response, extreme fatigue can sometimes signal a more serious health concern, such as hypothermia. Hypothermia occurs when the body loses heat faster than it can produce it, leading to a dangerously low core body temperature. Early signs of hypothermia can include intense shivering, confusion, and profound tiredness.
As hypothermia progresses, shivering may stop, and fatigue can worsen to the point of exhaustion, often accompanied by disorientation or slurred speech. Recognizing these symptoms is important, as untreated hypothermia can lead to severe health complications. If someone exhibits extreme tiredness along with confusion or loss of coordination in cold conditions, medical attention should be sought immediately.
Prolonged exposure to cold can also weaken the immune system, making individuals more susceptible to infections like the common cold or flu. These illnesses inherently cause tiredness as the body expends energy fighting off pathogens. Therefore, persistent fatigue in cold weather, especially when accompanied by other symptoms, warrants careful consideration.