Chill or Sweat: The Science of Thermoregulation
By Sarah Willis PhD.
If you are anything like me, sometimes our bodies are really challenged to regulate temperature. Let’s first figure out why it is so important for the body to adjust and keep a steady operating temperature. Thermoregulation is a homeostatic process to maintain a stable internal temperature regardless of changes in external conditions. It is like a narrow operating temperature range, which allows proper function for enzymes, processes, and cells.
Thermoregulation is directed by the hypothalamus, an area of our brain that produces hormones to act as our body’s thermostat. Cool! In a way, our hypothalamus checks our temperature and compares with the normal temperature and then responds to adjust based on the need. So, the central nervous system works in our body for thermoregulation to maintain our physiologic core body temperature by balancing heat generation and loss. Our body’s normal temperature should be around 98.6° F or 37° C. If we look a bit deeper, this process uses feedforward thermosensory information on the environmental temperature by sensing temperature using skin thermoreceptors to collect information from our skin and internal organs. Further, thermoregulation works to balance heat between production and loss. Specifically, heat production is mostly caused by the body’s metabolic processes to break down food into energy including primarily muscle activity. Where heat loss most often occurs through radiation where heat is released from the body surface and then evaporation of sweat from the skin (also considering direct contact with colder surfaces and movement of air around the body). We also have physiological responses to alter body temperature from involuntary responses to generate or dissipate heat, such as sweating, shivering, narrowing/widening of blood vessels to retain or release heat, respectively. In addition, we often choose behavioral responses such as changing clothing choice, use of shade, shower temperature, huddling for warmth, drinking beverages, etc. to modify exposure to heat or cold based on needs.
We can imagine what affects our body temperature…that would be the environment whether 
it is hot or cold outside as well as the activity of hormones regulating our body temperature such as estrogen and progesterone (in both men and women, more on that later). But what happens when our body temperature changes? If our body temperature is too high, the hypothalamus triggers the release of heat through sweat and dilation of blood vessels (this also lowers blood pressure) to cool the body down. While if body temperature is too low, the hypothalamus will relay information through the sympathetic nervous system to the body for heat generation to warm the body up by increasing the heart rate, constricting the blood vessels which also increases blood pressure, and shivering. Additionally, we might obtain a fever, which is a trigger from the hypothalamus where it sets the body’s temperature higher than normal as a reaction to germs or substances the body produces.
There are also extreme body temperatures that we are aware of: hypothermia, body temperature below 96° F or 35° C which can lead to brain damage, cardiac arrest, or death; and heat stroke, body temperature rises to 104° F or 40° C or greater which can also lead to brain damage or death.
As mentioned above, there are hormones produced by the hypothalamus that regulate body temperature. Specifically The best tips for reducing body temperature include drinking cool liquids, exposing your body to cooler air, getting wet in cool water, applying cold to key points of body (ice cubes/packs), moving less to decrease energy expenditure, wearing lighter and more breathable clothing, monitoring thyroid health, and possibly considering supplements. While the best tips for increasing body temperature revolve around wearing layers of clothing, drinking warm beverages such as tea or soup, eating warm meals, performing physical activities like walking or jumping jacks to increase energy demand, using heating pads, covering the head and extremities, and staying in a warm environment.
Estradiol is a primary form of estrogen to promote heat dissipation via vasodilation and ultimately lowering blood pressure and temperature. In addition, progesterone promotes heat conservation and higher body temperatures. The roles of both estradiol (estrogen) and progesterone are crucial for body temperature regulation in both men and women, though more prominently studied in women related to the menstrual cycle.
With that cleared up, let’s zoom in for a moment on fluctuations of these hormones in women over the course of the menstrual cycle. Low levels of estrogen can cause heat intolerance, which is most prominent in perimenopause/menopause which often results in hot flashes and night sweats. For the rest of us, as we see in the images below, the fluctuations of estrogen/estradiol are higher in the follicular and ovulation phases (heat dissipation, lower body temperatures) and lower in the luteal phase where progesterone is higher (both heat conservation and higher body temperatures). This is quite interesting, have a look.
Individuals can have problems with regulation of body temperature from main causes of infections, extreme weather, medication use, and a variety of health conditions, which may lead to an emergency. If someone gets hot and cold easily, there may be dysfunction of the hypothalamus which can cause temporary overheating (hot flash) or chilling (cold flashes).
Additionally, there are some deficiencies which can contribute to dysregulation of body temperature. Typically, a lack of vitamin B12 or iron can lead to feeling cold, where specifically an iron deficiency can slow down thyroid function and cause hypothyroidism making you feel cold as well. On the contrary, magnesium, potassium, and omega 3s can support temperature regulation.
A poorly functioning hypothalamus will result in an inability to regulate blood pressure, limitations leading to water retention/dehydration, elicit weight loss/gain without changes in appetite, fluctuations in body temperature, and muscle loss/weakness.
My personal experiences and thus increased interest in this topic are related to the impact of stress and energy level on body temperature regulation. What do we know about that?
Stress releases hormones such as adrenaline and cortisol, which lead to increased metabolic rate, and thus increased heat production. If this is an acute stress, we see a temporary rise in body temperature. While if this stress is a chronic stimulus, there is disruption in normal regulation leading to persistent slightly higher temperatures or fluctuations (depending on the individual and stressor).
Higher metabolic activity from stress can deplete energy stores and lead to fatigue. This places greater stress on the sympathetic nervous system and function of the hypothalamus to regulate body temperature.
As always in physiology, there are several parameters to consider how the body regulates temperature. These include: severity of the stressor related to the intensity and duration of stress as it impacts the magnitude of temperature change; individual variations regarding sensitivities to stress which varying the degrees of temperature fluctuation; and environmental temperature related to the influence of external temperature.
Becoming more sensitive to your own body’s temperature regulation and sensations you experience will guide you to take appropriate actions to maintain homeostasis. This is vital for your health and will translate to improvements in performance.