Traditionally, the “normal” body temperature for a human is considered to be around 37°C (98.6°F). However, more recent studies have suggested that the average body temperature might be slightly lower, closer to 36.8°C (98.2°F). Variations are normal depending on factors like the time of day, individual differences, and measurement method.
The animal kingdom and our closest relatives
Humans tend to have a slightly lower temperature than most other species. It may indicate the excessive needs of our larger-than-average brains which need to cool down to function properly.
- The body temperatures of our closest relatives, the great apes (which include chimpanzees, bonobos, gorillas, and orangutans), are similar to humans, generally around the 37°C (98.6°F) mark. However, individual variations and measurement conditions can affect this.
- Other primates, such as smaller monkeys, also have body temperatures roughly in this range, but again, there are species-specific differences and variations based on size, habitat, and metabolism.
In the animal kingdom, there is a variation in terms of normal body temperature. This may mean that what we know from animal studies may not necessarily apply to human beings.
- Birds: Often have higher body temperatures than mammals. For example, the body temperature of a chicken can be around 41°C (106°F).
- Dogs: Their normal body temperature ranges between 38°C to 39.2°C (100.5°F to 102.5°F).
- Cats: Typical body temperature is between 37.7°C to 39.2°C (100°F to 102.5°F).
- Elephants: Their average body temperature is about 35.9°C (96.6°F), which is slightly lower than that of humans.
It’s worth noting that while we share a lot of genetic material and physiological characteristics with the great apes, many factors affect body temperature, including size (larger animals tend to have lower metabolic rates and hence lower body temperatures), metabolism, habitat, behavior, and evolutionary history. The similarities and differences in body temperatures among species reflect a combination of these factors.
Human body temperature changes
Body Temperature Fluctuations Throughout the Day and Night
Human body temperature is not constant; it follows a circadian rhythm. It’s typically at its lowest in the early morning hours (around 2 a.m. to 4 a.m.) and peaks in the late afternoon or early evening.
Eating and Digesting:
After eating, especially large meals, the metabolic rate increases to break down food, a phenomenon known as thermogenesis. This can lead to a temporary increase in body temperature. Foods high in protein or spicy foods might lead to a more pronounced increase.
Exercising and Physical Activity:
Physical activity and exercise produce heat as muscles are used. As a result, core body temperature rises. To compensate and cool the body down, blood flow to the skin increases, and sweating occurs.
Sleep Cycles:
During the REM phase of sleep, the body’s temperature regulation is different than during wakefulness. The body tends not to shiver or sweat, even if temperatures drop or rise beyond typical comfort levels. Overall, body temperature drops during sleep.
Stress:
Acute stress can lead to an immediate increase in heart rate and metabolism, which can raise body temperature. Chronic stress might also impact temperature regulation, though the exact relationship can be complex and varies among individuals.
Other Factors:
- Women’s body temperatures can vary based on the menstrual cycle, typically seeing a rise post-ovulation.
- Illness, especially infections, can cause a fever, raising the body’s set point for temperature.
- External factors such as ambient temperature, humidity, and clothing also influence body temperature.
The body’s temperature regulation system is intricate, working to ensure that vital biochemical processes can occur at optimal rates. Deviations from the “normal” body temperature of around 37°C (98.6°F) can be indicative of physiological changes, illnesses, or external influences.
Cold therapy and longevity pathways
Cold therapy, often termed cold exposure or cold thermogenesis, has garnered attention in the wellness and longevity communities due to its potential health benefits. Shivering and the activation of brown adipose tissue (BAT) are two primary physiological responses to cold exposure. Here’s how these mechanisms may be related to longevity pathways:
Brown Adipose Tissue (BAT) Activation:
- Thermogenesis: Unlike white fat, which primarily stores energy, BAT burns energy. When you’re exposed to cold, BAT is activated to produce heat in a process known as non-shivering thermogenesis. This process helps maintain body temperature.
- Metabolism and Energy Expenditure: BAT activation leads to increased energy expenditure, which can influence metabolic health and potentially aid in weight management.
- Mitochondrial Function: BAT is densely packed with mitochondria, which are the powerhouses of the cell. Cold exposure can increase mitochondrial biogenesis and function in BAT. Enhanced mitochondrial function is associated with improved cellular health and longevity.
Shivering Thermogenesis:
- When the cold exposure exceeds the capacity of BAT to maintain body temperature through non-shivering thermogenesis, shivering, a rapid involuntary muscle contraction, begins. This process generates heat and represents an acute metabolic adaptation to cold.
Hormesis and Cold Exposure:
- Hormesis refers to the beneficial effects resulting from exposure to low doses of an agent or influence that is harmful at higher doses. Cold exposure can act as a hormetic stressor.
- This stressor can activate various cellular defense pathways, enhancing cellular resilience, and resistance to subsequent stress.
- Some studies suggest that repeated cold exposure can increase the levels of antioxidant enzymes, heat shock proteins, and other protective factors.
Potential Longevity Pathways Activation:
- AMPK: Cold exposure can activate AMP-activated protein kinase (AMPK), a cellular energy sensor. AMPK activation has been linked to various health benefits, including improved mitochondrial function and cellular stress resistance.
- SIRT1: Cold exposure can also increase the activity of sirtuin 1 (SIRT1), an enzyme associated with cellular health, DNA repair, and longevity.
- mTOR: Cold stress might modulate the mammalian target of rapamycin (mTOR) pathway, which, when inhibited, has been associated with lifespan extension in various organisms.
Energy and Resource Preservation:
- Repeated cold exposure may lead to an increase in BAT volume and activity, potentially improving metabolic efficiency over time. This can enhance the body’s ability to generate heat using stored energy efficiently.
Potential Limitations and Concerns:
- It’s essential to approach cold therapy with caution. While short, controlled exposures can offer benefits, prolonged exposure can be harmful and lead to hypothermia or other adverse effects.
- The specific impacts on longevity in humans remain an area of active research, and while there are promising signs, there’s no definitive evidence yet that cold exposure extends human lifespan.
Doing cold therapy safely
Cold therapy, when done without proper precautions, can pose risks. It’s vital to understand both the benefits and the potential dangers associated with cold exposure. Let’s explore the risks, the methods of cold therapy, and the conditions for benefitting from this approach.
Why Cold Therapy Can Be Dangerous:
Hypothermia: This is the most significant risk. It occurs when the body loses heat faster than it can produce heat, causing a dangerously low body temperature. Symptoms can include intense shivering, drowsiness, confusion, and slurred speech.
Frostbite: This is the freezing of skin and underlying tissues. Fingers, toes, and the face are especially prone. Early signs include numbness, tingling, or pain in the affected area.
Cold Water Shock: Suddenly entering cold water can cause an involuntary gasp reflex, which can lead to inhalation of water and potential drowning. It can also cause rapid heart rate and increased blood pressure.
Immune System Suppression: Repeated cold stress may temporarily suppress immune function, making one more susceptible to illness.
Underlying Health Conditions: People with certain health conditions, like heart disease, might be at increased risk during cold exposure due to the stress it places on the heart.
Ways to Exercise Cold Therapy:
Sleeping with Fewer Blankets: This is a milder form of cold exposure. It might help train the body to function better in cooler environments without pushing it too hard.
Walking Outside with Fewer Clothes: This provides a moderate amount of cold exposure and allows for more gradual acclimatization.
Cold Showers: Starting with lukewarm water and gradually reducing the temperature can help the body acclimate. Cold showers can last for several minutes to up to 20 minutes.
Ice Baths: This is an intense form of cold therapy. Immersion should be limited to a few minutes initially, and one should never do it alone due to the risks involved. It’s often used by athletes for recovery.
Whole Body Cryotherapy: This involves standing in a chamber where the air temperature is lowered to well below freezing for a couple of minutes. It’s crucial to follow safety guidelines and ensure the procedure is done correctly.
Conditions for Benefitting from Cold Therapy:
Shivering: This is a clear sign the body is experiencing significant cold stress. Shivering activates brown adipose tissue (BAT) and increases energy expenditure.
Consistency: Just like exercise, the benefits of cold therapy might be more pronounced with regular and consistent exposure, as the body adapts and becomes more efficient over time.
Avoid Overexposure: It’s essential to start slowly and not push the body too hard, especially initially. Listening to the body and knowing when to stop is crucial. Overdoing it can lead to the risks mentioned above.
As with any intervention, it’s important to approach cold therapy with caution and to consult with a healthcare professional, especially if you have underlying health conditions or if you’re trying more intense forms of cold exposure for the first time.
References
- Lee, P., et al. (2014). Temperature-acclimated brown adipose tissue modulates insulin sensitivity in humans. Diabetes, 63(11), 3686-3698.
- Lombard, D. B., et al. (2011). SIRT1: A conserved deacetylase affecting stress resistance, genomic stability, and aging. Mechanisms of Ageing and Development, 132(4), 225-229.
- Cantó, C., & Auwerx, J. (2009). PGC-1α, SIRT1 and AMPK, an energy sensing network that controls energy expenditure. Current Opinion in Lipidology, 20(2), 98-105.