A study showing the effect of humidity and temperatures on the human body and what is the lowest and highest temperature that the body can tolerate

Weather of Arabia - Temperatures all over the world rose dramatically during the heat waves that affected the month of July, which raised doctors' warnings of negative health effects and worried climate scientists. In addition to setting many records in many regions, in addition to breaking the record for the highest day temperature on Earth several times during July 2023.

What happens in the human body at a temperature of 40 °?

According to new research from the University of Roehampton in England, the human body may lose the ability to get rid of excess heat and stop functioning properly when outside temperatures reach over 40°C (104°F).

What is the thermoneutral zone?

A thermoneutral zone is the range of temperatures in which the human body does not need to expend extra effort, energy, and increased metabolic rate to maintain its ideal core temperature of 37°C or 98.6°F.

What is the lowest temperature in the thermoneutral zone?

Studies show that the lower limit of the neutral temperature zone is 28 degrees Celsius or 82.4 Fahrenheit . Below this point, the body expends more energy to maintain its optimum temperature. One of the main ways the body controls this is by shaking/shivering, where major muscle groups contract involuntarily to produce heat

At higher temperatures, the body uses other mechanisms to cool down, such as perspiration and dilatation of blood vessels on the surface of the skin to lose heat.

What is the highest temperature in the thermoneutral zone?

Although the lower temperature of the neutral thermal zone has been determined, the upper limit is still uncertain.

One study suggests that the upper limit may stand at around 32 degrees (89.6 degrees Fahrenheit) at which a person begins to sweat. However, another study noted that the metabolic rate begins to increase at 40°C (104°F) .

Further research into the upper bound of the TZ could inform policies regarding working conditions, sports, medical treatments, and international travel.

As a follow-up study to the 2021 investigation, researchers at the University of Roehampton in England conducted a second set of experiments to investigate the upper bound of the thermoneutral zone. They found that the upper limit of the thermoneutral zone is most likely between 40°C (104°F) and 50°C (122°F).

"The results appear to shed more light on the body's responses to constant heat and humidity, and on both the nature and mechanisms of the enhanced metabolic rate that also arises in response to such conditions," according to Dr. G. Weiss Ulm, a bioinformatics research scientist and medical data expert at the Institutes National Health Institute, who was not part of the team of researchers involved in the study, told Medical News Today.

How does temperature and humidity affect the human body?

For this study, the researchers recruited 13 healthy volunteers, ranging in age from 23 to 58 years old. Among the participants were 7 females.

Each participant was exposed to five temperatures for one hour while resting.

The conditions tried were as follows:

• 28°C (82.4°F) and 50% humidity.
• 40°C (104°F) and 25% humidity.
• 40°C (104°F) and 50% humidity.
• 50°C (122°F) and 25% humidity.
• 50°C (122°F) and 50% humidity.

During each temperature condition and at the initial state (before the experiments began), the researchers recorded several metrics, including:

• The temperature of the core and skin.
• blood pressure.
• sweating rate
• heart rate
• breathing rate.
• Volume of inhaled and exhaled air per minute.
• movement levels.

In the end, the researchers found that the participants' metabolic rate increased by 35% when exposed to a temperature of 40°C (104°F) and an air humidity of 25%, and increased by 48% at a temperature of 40°C (104°F) and an air humidity of 25%. 50%.

Although conditions of 50° C (122°F) and 25% air humidity did not increase metabolic rate compared to conditions of 40°C (104°F) and 25% air humidity, only The metabolic rate under these conditions was 56% higher than in the initial condition at 50°C (122°F) and 50% air humidity.

An increase in metabolic rate under conditions of 40°C and 25% air humidity was not associated with an increase in core temperature. However, in conditions of 50°C and 50% humidity, participants experienced a rise in core temperature of 1°C, or 1.8°F.

The researchers note that these results indicate that the body is capable of expelling heat at a temperature of 40°C (104°F), but not at a temperature of 50°C (122°F). This means that the body has difficulty controlling temperature and getting rid of excessive heat at higher temperatures.

“It appears that results may vary based on humidity,” Dr. Mark Guido, an endocrinologist with Novant Health Forsyth Endocrine Consultants in Winston-Salem, North Carolina, who was not part of the study team of researchers, told Medical News Today.

He added, “In the study, there was some evidence that resting metabolic rate was higher in higher humidity, even at the same temperature. Humidity also appears to play a large role in metabolic rate.”

The researchers also noted that participants in conditions with a temperature of 50°C and an air humidity of 50% sweated 74% more and experienced a 64% increase in heart rate compared to the initial condition.

The researchers added that compared to the initial condition, the participants in the 50°C and 50% air humidity group felt an increase in cardiac muscle load, meaning that their hearts needed more oxygen to maintain optimal function.

Moreover, their breathing rate also increased by 23% , and the amount of air they could inhale and exhale per minute increased by 78% .

The researchers noted that drinking water in every temperature condition did not cool the body.

How does climate affect metabolism and health?

MNT asked Dr. John B. Higgins, MD, a sports cardiologist at McGovern Medical School at the University of Texas Health Science Center at Houston (UTHealth), who was not involved in the study, on how living in different climates affects your metabolic rate and the thermoneutral zone.

Dr. Higgins notes that people who live in warm climates tend to acclimatize and not increase their body temperature and thus their metabolic rate as much. Similarly, people who live in areas with cold or freezing temperatures may have a greater response to heat exposure because they are not heat acclimated to the same extent.

MNT also spoke with Dr. Ulm and said: "In general, the body finds ways to activate the various feedback loops necessary for self-balancing, i.e. the strenuous regulation of physiological processes that allow the complex biochemistry of organs and tissues to be conducted efficiently and correctly."

“Body temperature and metabolic rate are two key parts of this, and for those who live in hot regions all year round, compensatory feedback loops may be more likely to be active and effective. This may be attributed to both heritable factors – of societies in such These conditions in the long term - and to short-term adaptations in general."

"It's similar to the way permanent residents of high altitudes will adapt compensatory mechanisms in, for example, red blood cell physiology and other aspects of oxygen-carrying capacity, both acutely - such as iron turnover rates - and chronically."

What are the limitations of the study?

MNT spoke with Dr. Ulm about this and pointed out the following

"As always in studies like these, there is a question about how representative the cohort sample of participants is of the general population and specific populations surveyed, relative to the physiological traits and responses measured."

He added, "Studies in this case have also been particularly challenging given the surrounding circumstances, and there are also enduring issues regarding the applicability of the empirical environment to real-world relationships."

"It's hard to draw realistic conclusions from a small lab study, but my main conclusion is that elevated heat stress appears to increase resting metabolic rate by making it harder for the body to try to stay cool, particularly by causing a significant increase in body temperature," Dr. Guido noted. Heart rate If this were true in real-world conditions, it could slightly increase cardiovascular disease by putting more stress on the heart.

Also read: What is the highest temperature the human body can withstand?

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Source: medicalnewstoday