Heat Intolerence

                                                       Heat Intolerance.

                                                   PKGhatak, MD

Heat intolerance is not a disease; it is a symptom. Some might say, “It is too hot in here,” and others might look at him in surprise because they feel comfortably cold in the same room.

The question is, who is right, or is there a medical explanation for this temperature perception difference between people.

Yes, there is a physiological reason for heat intolerance.

The Heat Center is located in the brain, and is connected with the skin and the internal organ temperature receptors., The Heat Center (HC) is located in the Hypothalamus of the brain, which is connected with the pituitary endocrine gland, which in turn is connected with the sympathetic and parasympathetic nervous systems.

By varying the output, the heat center of the body can maintain a constant core temperature throughout the winter and summer.

Source of body heat.

The human body derives heat from 5 separate sources:

1. Basal metabolism

 2. The specific dynamic action of food,

 3. Physical activities

 4. Shivering 

  5. Non-shivering thermogenesis.

Heat Center regulates temperature settings, but the metabolic process generates heat. It is like a computer; multiple programs are running in the background. The metabolic process continues at all times during the lifetime of the individual. The organ functions continue at a basal, and is called Basal metabolism. In humans, the Basal Metabolic Rate (BMR) is 76 kilocalories/Kg body weight /Hour. This is the main source of body heat.

2. Specific dynamic action of food (SDA). The process of digestion of food generates heat. Protein gives out the most heat, about 20 % of the calories contained in protein food. This is the reason we feel comfortably warm after eating a steak.

3. Physical activities. All forms of physical activities generate heat,

4. Shivering. Exposed to cold and wind, the body begins to shiver. Muscle contractions generate body heat.

5. Non-shivering thermogenesis: It takes place in Brown Fat and muscles. Adrenaline is released at the sympathetic nerve terminal of brown fat tissue and muscle. Adrenaline accelerates the conversion of fatty acids and glucose to heat, ketones, H2O, and CO2.

Excessive body heat and heat intolerance:

1. Menopause is due to falling sex hormone levels. Various symptoms, mostly due to the perception of excess heat produce the symptoms of menopause.

 2. Hyperactive thyroid gland.  Excessive secretion of Thyroxine (hormone of the thyroid gland) increases BMR, generates fine muscle tremors, and increases heart rate and blood pressure. Catabolism of fatty tissues and muscles produces excessive heat.

Drug abuse. Amphetamines, cocaine, antipsychotic, and antidepressant drug use generate a sense of excess body heat.

Anticholinergic drugs. Anticholinergic drugs decrease sweat production and prevent cooling from evaporation and loss of heat. The core body temperature rises.

Caffeine. It is a cardiovascular and neuronal stimulant. It produces small vessel constriction and decreases heat dissipation. A mild increase in temperature is usual in therapeutic doses. In posing, caffeine raises the core temperature. 

Heat stroke. When exposed to high heat in a humid environment, the body fails to dissipate heat by radiation and evaporation. The core temperature rises and derails the functioning of metabolic and enzyme systems. It turns into an emergency situation, and can permanently damage the brain and heart, and even death.

Malignant Hyperthermia. This is another life threatening medical condition. It is an inherited disease inherited as an autosomal dominant trait. exposed to volatile anesthetic agents during general anesthesia, large amounts of calcium leave the calcium stores and enter the skeletal muscle fibers. Increased intramuscular calcium produces sustained muscle contractions. An excessive amount of heat is generated. Blood vessels may contract for a long time and can cut off blood flow, which is called Rhabdomyolysis. The released myoglobin from the necrotic muscle can block the kidney filters, producing metabolic acidosis and hyperkalemia (high serum potassium). Followed by cardiovascular collapse and death even death. 

Multiple sclerosis.  In Multiple sclerosis, the demyelination may directly affect the hypothalamus and the autonomic control center. Excessive heat generation may also be accompanied by derailed heat dissipation because of spinal cord lesions in multiple sclerosis.

Diabetes mellitus can damage the autonomic nervous system, and excessive heat and fluctuation of body heat may result.

Multisystem atrophy of the nervous system. The autonomic center damage is the result of increased heat.

edited May 2025.

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