CORE TEMPERATURE & CIRCADIAN RHYTHM

CORE TEMPERATURE & CIRCADIAN RHYTHM

clock with human hands around it

Did you know that your body temperature normally fluctuates up to 1°C (~1.8°F) in a day? But why?\

Photo by Oladimeji Ajegbile on Unsplash

THE DAILY CORE TEMPERATURE CYCLE

Your core temperature is lowest around 4-6 AM and highest around 4-7 PM. Biological circadian rhythms are ~25 h in length, and so the time of day these peaks and troughs occur will slightly shift each day.

This is important to remember when working in the heat, because your core temperature will always be lower in the morning than in the afternoon, and so it is important to understand whether your core temperature is increasing as a result of heat stress or just due to typical fluctuations in body temperature throughout the day.

WHAT CAUSES THIS CORE TEMPERATURE FLUCTUATION?

The short answer: melatonin. Melatonin is a hormone that has a tight control on your body temperature: when your body increases melatonin at night, this leads to a decrease in your body temperature (by ~0.3°C) and causes you to get sleepy. This is one of the reasons that taking melatonin might help you fall asleep.

However, studies have shown that melatonin does not reduce your body temperature enough to help you stay cooler in the heat.

construction site

HOW DOES THIS CORE TEMPERATURE FLUCTUATION AFFECT YOUR ABILITY TO WORK IN THE HEAT?

Although your ability to dissipate heat is just as good in the morning as in the afternoon, the slightly higher core temperature in the afternoon can reduce your productivity because you might achieve a higher core temperature sooner. That means you might need to take more breaks to stay cool in the afternoon vs. the morning work shifts.

One solution is to try to get all of your hard work done in the morning when it’s cooler outside and your body temperature is lower, and to save the smaller, lighter work tasks for the afternoon.

Have more questions? Kenzen is here to help with our Heat Safety Training Program.

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REFERENCES:

1) Racinais, S. “Different effects of heat exposure upon exercise performance in the morning and afternoon.” Scandinavian journal of medicine & science in sports 20 (2010): 80-89.

2) Cheung, Stephen S. Advanced environmental exercise physiology. Human Kinetics Publishers, 2009.

WHEN YOU’RE TOO HOT: FEVER VS. HEAT ILLNESS. WHAT’S THE DIFFERENCE?

WHEN YOU’RE TOO HOT: FEVER VS. HEAT ILLNESS. WHAT’S THE DIFFERENCE?

Both infection and heat stress can lead to dangerously high core body temperatures.

But how can you tell the difference these 2 things physiologically, and should they be treated differently?

thermometer

With the rapid spread of the coronavirus (SARS-CoV-2/COVID-19), the Kenzen team wanted to make sure that anyone who might be continuing to work (or live) in hot climates is aware of the the differences between heat-related illnesses (e.g., exertional heat exhaustion or heat stroke) vs. fever, so that you can stay safe.

Body Temperature Regulation: The Basics

Your body wants to maintain it’s temperature around a ‘“set-point” where it’s most comfortable and works most efficiently. This set-point is typically around 97.9 to 98.8°F (~36.6-37.1°C). Of course, this set-point differs for each individual— based on how fit they are, whether they are heat acclimatized, and what time of day it is— but in general, your body tries to maintain its temperature within this narrow range.

This set-point is controlled by a region in your brain called the hypothalamus, where a group of cells (neurons) sense changes in your body’s temperature and then send out responses to adjust the temperature accordingly. There are also neurons in your skin that sense hot and cold, and then relay this information to the brain. Your brain combines all of this information together and if your temperature is outside of that set-point, it will cause your body to respond by either increasing (e.g., through shivering) or decreasing (e.g., through sweating) your temperature to get it back to normal.

brain

So what happens with a fever?

  • A fever just indicates that your body temperature is higher than normal. This is typically above 100.4°F (~38°C) and occurs from an infection (either viral or bacterial) that is causes substances, called pyrogens, to leak outside of the invader cells.

  • These pyrogens increase the body’s set-point, which means that now instead of having a set-point of say 97.9°F, your new set-point is 103°F.

  • Because you have a new (higher) set-point, your body now thinks that a temperature of 97.9°F is “cold”, and so your body will try to increase your temperature.

  • This causes the typical responses when you’re cold, like 1) shivering (chills), 2) vasoconstriction (narrowing) of the vessels in your skin which makes your skin colder because there is less blood flowing to the skin, and 3) increased cellular metabolic heat production.

  • All of these responses cause your body temperature to go up. It continues to go up (in some cases for hours) until your temperature hits this new set-point of 103°F. At this point, you might feel OK because you’re at your “new normal.” However, as soon as you cross this point, or you take medications that inhibit the pyrogens, your body set-point goes back down, and now your body temperature is way too high.

  • What does your body do? That’s right, it tries to cool you down by sweating, vasodilation, etc… which is when you feel really hot and sweaty.

  • This cycle of shivering and sweating can continue for as long as you are fighting the infection.

How do you know if you have a fever?

If you ARE NOT working/exercising in the heat, and you feel chills or cold skin, have body aches, and/or feel weak & tired, you may have an infection that should be treated by a medical professional.

Note: If you ARE working in a hot environment, and your core temperature does not feel like it has been increasing steadily, you are intermittently getting chills, and/or you feel cold or achy, you might have something that is unrelated to heat stress.

What’s the best way to treat a fever?

Contact your doctor, stay home, drink plenty of fluids, and rest.

construction workers

What happens with heat-illnesses (like heat stroke)?

  • Unlike with a fever (from an infection), when you have a heat-related injury or illness, your body temperature (hypothalamic) set-point has not changed.

  • With heat stress, your core body temperature continues to increase past your set-point because your metabolic heat production (from working or exercising really hard in the heat) is exceeding your body’s ability to get rid of the heat you’re generating.

  • And once your core body temperature goes up past the set-point, then you start sweating to try to cool your body down. But remember, if it’s really humid and hot outside, then it won’t be as easy for you to dissipate that heat (because the sweat won’t evaporate).

  • So if you’re working hard in the heat, and you are producing heat faster than you can get rid of it, your body temperature will continue to climb.

  • Often, while working or exercising in the heat, core body temperatures can easily (& safely) exceed the “fever” criteria of 100.4°F. In fact, reaching this core body temperature is often necessary to acclimatize to the heat.

  • Most trained athletes & heat-acclimatized workers can safely reach and maintain core body temperatures of 101.3°F (38.5°C) without any damage to their body.

  • However, the main difference (between reaching this higher core temperature with heat stress vs. fever) is that this is a safe increase in core temperature that has not altered the brain’s set-point. And furthermore, your body is not too hot where you could get irreversible (organ) damage.

  • That being said, if people are not closely monitored for signs & symptoms of heat-related injuries & illnesses, these hotter temperatures can lead to heat stroke and even death.

How do you know if you have a heat-related illness?

Signs & symptoms can vary, but some of the first signs of heat exhaustion are really hot skin, very sweaty, feeling lightheaded or faint, difficulty continuing to work/exercise, and general weakness.

Exertional heat stroke means that your core body temperature is >104°F (40°C) and it is a serious medical emergency. Along with this extremely high core body temperature, the person will often exhibit changes in their behavior (e.g., aggressiveness, confusion, irritability), can collapse or faint, and is very weak.

The main point is that you will generally be feeling hot, sweaty, & faint with heat-related illness, more so than cold, chilly, & achy, like with a fever.

What’s the best way to treat heat-related illnesses?

For heat exhaustion: rest (for at least 15 min), drink water, and find shade or air conditioning. Continue to monitor your symptoms & if possible, track your body temperature throughout the day.

For exertional heat stroke: emergency cooling using an ice water bath is best, & call emergency medical services immediately. Remember: cool first at the site, and then transport to the hospital.

Stay safe & healthy, everyone!

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REFERENCE:

Guyton, Arthur C., and John Edward Hall. Textbook of medical physiology. 12th edition. Philadelphia: Saunders, 2011.

BATTLE OF THE SEXES: WHO DOES BETTER IN THE HEAT?

BATTLE OF THE SEXES: WHO DOES BETTER IN THE HEAT?

Watch our first Kenzen video blog with VP of Research & Development, Nicole Moyen, as she explores the differences between how men & women handle working in the heat.

If men & women are working at the same relative work-rate, then men typically have a higher sweat rate than women (assuming men have a larger body surface area to mass ratio).

Remember: sweating is the main way that we get rid of body heat.

This higher sweat rate in men means that:

  • In hot-dry (low humidity) climates, men will likely be able to work for a longer period of time with a lower core temp than women, because they are better able to get rid of body heat through increased sweating.

  • In hot-humid climates, women will likely be to work for a longer period of time in the heat (with a lower core temp) because their lower sweat rate will keep them from losing body water (through sweating) that isn’t evaporating or cooling.

    • Men, on the other hand, due to their higher sweat rate will be losing a lot of body water through sweating, but it won’t be evaporating in the high humidity. So men will become dehydrated more quickly vs. women, and see a faster increase in core temperature.

This information is important to keep in mind if you have men and women on your workforce, so that you consider the humidity and sex when determining work/rest schedules for your employees that day.

For help setting up work/rest schedules at your site and heat safety training, check out our Heat Safety Training Program.

WHAT YOU’RE CONSUMING CAN HELP YOU OR HARM YOU IN THE HEAT.

WHAT YOU’RE CONSUMING CAN HELP YOU OR HARM YOU IN THE HEAT.

There are several supplements that can help or harm you in the heat, and it might not be what you think…

crumpled cigarette packs

We have all seen the overwhelming wall of pills, powders, and tonics claiming to help cure every disease known to man. Some of these supplements even claim to help with working in a hot environment. But do they work?

The short answer is… maybe.

By definition, a supplement is exactly that. Not a replacement or a stand alone food item, but a supplement to your day to day nutrition. And as is the same with most supplements, they are generally only useful when we are lacking in our normal nutritional health.

TWO SUPPLEMENTS THAT MIGHT HELP YOU IN THE HEAT:

Creatine:

Creatine is one of the most popular nutritional supplements in the world. While most people tend to take creatine to increase muscle size with weightlifting, there is major concern that creatine can lead to muscle cramping, primarily from dehydration.

It was once thought that because creatine causes more water to be held in the muscle cells, it would lead to dehydration.

However, research has shown us that these fears are not only unnecessary, but reversed! Scientists now believe that creatine may actually improve our tolerance to the heat. It turns out that the extra water held in the muscle cells may actually enhance our body’s ability to deal with heat stress.

Take action: For optimal results, start with 20 g/day for one week, followed by a maintenance dose of 5 g/day thereafter. Unlike Vitamin C, it is hard to get enough creatine naturally from your diet, so supplementing with creatine is the best way to increase levels.

Vitamin C:

Although research is conflicted, it has generally been shown that taking a Vitamin C supplement can lower core body temperature during the first few days of heat acclimatization, thus minimizing the risk of heat-related injuries and illnesses.

Moreover, although the amount of vitamins lost through sweating is minimal, research indicates that for individuals who have a diet lower in Vitamin C and are consistently working in the heat (and sweating a lot), can benefit from taking a daily dose of Vitamin C to help replenish stores that are lost through sweating.

Take action: For optimal results, take 250 mg/day, and not more than this amount because it can compromise the absorption of vitamin B12.

ONE THING THAT DOESN’T HELP OR HINDER YOU IN THE HEAT

Caffeine:

While caffeine tends to be a bit confusing as to its effects on overall health, research has shown that caffeine does not seem to affect performance in the heat or increase the risk of heat illness. And if you are a regular coffee or tea drinker, research shows that regular consumption of coffee or tea will not dehydrate you. So while caffeine may not help you beat the heat, it won’t hurt you either.

THINGS THAT CAN HARM YOU IN THE HEAT

Nicotine:

Consistent nicotine use (in the form of tobacco, cigarettes, etc) can impair your ability to get rid of body heat because nicotine use alters your sweating and skin blood flow mechanisms, making you more susceptible to heat-related injuries and illnesses. Even short-term nicotine use in the heat can be dangerous because nicotine is a stimulant, which leads to increased heart rate and blood pressure, meaning that your cardiovascular strain will not only be higher from the heat, but also from the nicotine. It’s best to avoid nicotine-related products altogether.

Alcohol: 

While alcohol can lead to vasodilation, which in theory, would help to dissipate heat, the slight benefit does not outweigh the harm. Alcoholic drinks (>4% ABV) lead to increased urination (they act as a diuretic), which can dehydrate you. This means that if you’re drinking alcohol after a long day of working in the heat, you probably will not replenish the body water you lost that day through sweating, and so you will start the next work day dehydrated.

This of course is a problem because dehydration exacerbates the effects of heat stress on the body by reducing sweat rate and skin blood flow— the two key mechanisms to get rid of body heat— and also increases the cardiovascular strain on your body. This means that you won’t be able to work as hard or be as productive at work when dehydrated, and you are also more susceptible to heat-related injuries and illnesses.

Moral of the story: be aware of the things you’re consuming that might help you, but can also harm you in the heat. 

AND REMEMBER THAT HEAT ILLNESSES ARE 100% PREVENTABLE!

For more information on emergency cooling procedures, or to have Kenzen make your worksite heat-safe, see our Heat Safety Training Program.

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REFERENCES

  1. https://doi.org/10.1007/s00726-016-2237-9
  2. https://www.ncbi.nlm.nih.gov/books/NBK236216/
  3. Pryor, J. L., Périard, J. D., & Pryor, R. R. (2020). Predisposing Factors for Exertional Heat Illness. In Exertional Heat Illness (pp. 29-57). Springer, Cham.
3 THINGS YOU NEED TO KNOW ABOUT WORK/REST SCHEDULES

3 THINGS YOU NEED TO KNOW ABOUT WORK/REST SCHEDULES

WORK/REST SCHEDULES CAN HELP PREVENT HEAT INJURY & ILLNESS ON HOT DAYS.

BUT THERE ARE 3 IMPORTANT THINGS YOU NEED TO KNOW BEFORE ADMINISTERING THESE SCHEDULES TO YOUR WORKFORCE.

Construction worksite

  1. These work/rest schedules are not “one size fits all.” What does this mean? Well that a work/rest schedule of 30 minutes working and 30 minutes resting on a really hot day is not going to prevent heat injury or illness in ALL people. The research backing these work/rest schedules has largely been based upon young, healthy men, which means that other populations (older individuals, women, diseased populations) might need very different work/rest schedules.

    “…existing guidelines adopted and recommended for use by government agencies worldwide (e.g., WHO, CDC, others) to protect the public and workers also assumes a “one size fits all” approach to protect human health. These guidelines generally prescribe protective measures (e.g., heat advisories, exposure limits) using models defined by the assessment of heat strain in young and or relatively healthy adults. They fail to consider key factors such as sex, age, health status, and other factors, which can markedly alter a person’s tolerance to heat, thereby leaving a large segment of the population under-protected…(1)

  2. Work/rest schedules vary depending on the organization or governing body that developed them. For example, OSHA & the US Army use a similar work/rest schedule, while the EPA & ISO standards have slightly different recommendations. That being said, it’s important to understand how these recommendations vary, but more importantly, what factors they consider in giving the work/rest schedules (e.g., wet bulb globe temperature-WBGT, temperature, humidity, clothing, sun exposure, wind speed, etc).
  3. One of the biggest problems with work/rest schedules (especially those using WBGT), is that they severely underestimate the heat strain experienced by workers when the evaporative capacity (of sweat) is limited—like in very humid environments or under heavy clothing layers— this means that more workers will be susceptible to heat injury & illness when using WBGT-based work/rest schedules under these conditions. (2)

Table of WBGT Categories

Example of U.S. Army work/rest schedules (3)

SO IN ADDITION TO IMPLEMENTING WORK/REST SCHEDULES,

MAKE SURE YOU’RE ALSO DOING THE FOLLOWING 5 THINGS TO PROTECT YOUR WORKERS:

  1. First and foremost, you can get your workers set up with smart PPE, like the Kenzen patch, that will monitor workers’ physiological data real-time and alert you (and the worker) when their core temperature is reaching unsafe levels, so that they can take a break. This is completely individualized, which solves the problem of work/rest schedules not protecting all populations.
  2. During the rest periods, let your workers actually rest. DO NOT assign any other work tasks while they’re resting- your workers need to cool down, and if they continue to work, their core temperature will keep going up. (3)
  3. Keep checking the weather (WBGT, temperature, and humidity) throughout the day— we recommend every 2 hours— and update the work/rest schedules accordingly if the criteria change.
  4. During rest breaks: provide workers with potable water and shade or air conditioning, and allow them to remove any extra clothing that might restricting evaporative heat loss (i.e., that keeps the sweat from evaporating off of their skin). (5)
  5. If you don’t have a way of monitoring each worker’s individual physiology, then make sure you are attentive to each individual and whether they might be presenting any signs or symptoms of heat injury or illness. Let the individual stop working and rest if they need to (even if the working time limit hasn’t yet been reached). (4,5)

    Lastly, remember: these work/rest schedules were created for young, healthy men, so you will need to pay special attention to how older adults, women, and those with diseases are responding to these schedules on a hot day because they might need a completely different program to stay safe in the heat.

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REFERENCES:

  1. Kenny, G.P., Notley, S.R., Flouris, A.D. and Grundstein, A., 2020. Climate Change and Heat Exposure: Impact on Health in Occupational and General Populations. In Exertional Heat Illness (pp. 225-261). Springer, Cham.
  2. Budd, G.M., 2008. Wet-bulb globe temperature (WBGT)—its history and its limitations. Journal of Science and Medicine in Sport11(1), pp.20-32.
  3. Regulation, T.R.A.D.O.C., 2016. 350-29. Prevention of heat and cold casualties. Fort Eustis, VA: US Army Training and Doctrine Command, Publication TRADOC Regulation, pp.350-29.
  4. Coco, A., Jacklitsch, B., Williams, J., Kim, J.H., Musolin, K. and Turner, N., 2016. Criteria for a recommended standard: occupational exposure to heat and hot environments. control Ccfd, editor.
  5. https://www.osha.gov/heat/