June 14, 2022

Part 3 of our Cooling Plan Series is all about YOU!  In order to be able to talk about the multitude of risk factors with regards to the heat. We are breaking them up into three blog entries covering your personal risk factors, environmental risk factors, and risk factors which you control. Today, we will discuss personal risk factors for heat stress to help you make better decisions in your cooling plan. Depending upon how many of the proverbial boxes you check off you may want to consider lowering the temperature threshold for when a cooling plan is implemented or making a plan that incorporates more items to help you stay cool.  

 Age is a major and misunderstood factor in heat sensitivity. There are two groups that are at increased risk of heat related illness: the very young, and older adults.

There are very clear physiological reasons for higher risk within these two groups. Let’s start by talking about the youngest among us.

• Metabolic rate: Children grow up fast! All the growth that goes into making them taller, stronger, smarter humans means that their bodies are consuming more energy and producing more heat.

• Body surface area: Did you know that a human baby is born with more body fat than any other mammal? About 15%!  With that percentage of body fat, babies have a lot of insulation and not alot of surface area to expel excess heat to the environment.

• Blood circulation: Children have a lower blood volume than adults which limits the transfer of heat from our core to our extremities.

• Sweat: Children sweat less than adults and begin sweating at a higher body temperature.

• Fluid replenishment: As any parent trying to potty train a child can attest, children aren't aware of their bodies needs. Unless supervised, children are much less likely to drink adequate amounts of water to replenish fluids lost to sweating.

• Read more information on heat risks with children.
   

On the other end of spectrum older Americans report that they are more concerned about feeling cold than hot. The physiological changes that make older adults feel cold are the same that make heat a more dangerous risk than for younger people. Lets explore the same factors that affect our children and see how changes to our bodies lead to heat sensitivity as we age.

• Metabolic rate: As we age our metabolic rate slows, this leads to a lower resting body temperature and a feeling of being cold more often than being warm.

• Body surface area: Older adults have a thinner layer of fat under the skin, making them more susceptible to cold. Also, once we are done growing (upwards at least ) we have reached our maximum surface area. The more surface area we have the easier it is to expel heat to the environment. So, this should be a plus but…

• Blood circulation: As we age our blood circulation changes with our arteries becoming less flexible. This becomes noticeable first in our hands and feet which may feel colder as there is less warm blood flowing to these areas. However, it is important to remember from last week's blog that with less blood flowing to the extremities and the skin it’s much harder for our bodies to get rid of excess heat.

• Sweat: Sweat glands shrink and become less sensitive, reducing the sweat output and reducing our bodies ability to get rid of heat.

• Fluid replenishment: While as kids, we might not understand when our bodies  are telling us that we are thirsty, as we get older the thirst signal itself may weaken. So we may not realize when we  need water. It’s also important to note that our bodies generally have a lower water composition as we age, meaning we have less reserves of water and are more likely to become dehydrated.

"The rate of heat-related deaths among persons aged ≥65 years was 0.7 per 100,000 population, the highest across all age groups." 
https://www.cdc.gov/mmwr/volumes/69/wr/mm6924a1.htm

The next risk factor is how fit we are.  If we remember from last week's blog, excess heat puts a significant amount of stress on our hearts as they  work double time to pump blood to our organs and muscles to keep them running smoothly while it also has to push all the excess heat away from the core of our bodies  to our extremities. The better shape that we are in means our hearts are more efficient at fulfilling these two tasks. Up here in Rochester, NY we hear a lot about “Heart Attack Snow” due to how strenuous shoveling, especially heavy wet snow, can be on our  hearts. It’s  important to recognize that heat can have the same effect on our hearts if we are not physically prepared for it.

There are many medical conditions that increase our risk of heat related illness. The reasons these conditions do this are many but we will break them up into two categories; heart related and neurological. Many medical conditions affect our heart and circulatory system, such as Diabetes, Hypertension, and even being pregnant. As we have talked about heat puts added strain on our hearts. Any medical condition that affects the heart is going to increase our risk in the heat. With diabetes there is added concern, High temperatures and heat can change how our bodies use insulin. We  may need to test our blood glucose more often and adjust our insulin dose and what we eat and drink.

Many neurological conditions, like Lupus and Fibromyalgia, also affect our relationship with the heat. Some of these are less understood medically and may have to do with a lower response in the hypothalamus , which helps keep our  body at a stable state. In demyelinating diseases, like Multiple Sclerosis, the erosion of the insulation of our nerves causes problems in both hot and cold environments. Heat sensitivity is a well documented symptom of MS and is referred to as Uhthoff's Syndrome. This is where pseudo exacerbations of the disease occur when the body is overheated.

Recent exposure to heat has major implications for your body. Our bodies are amazing and complicated machines. When we experience new environmental conditions over time our bodies learn to adapt. It is amazing how the first 80F / 27C degree day in spring can feel so much hotter than the common 90F / 33C day in summer.

This is called acclimatization and many physiological changes occur when our bodies are acclimatized to the heat. There is a stabilization of blood circulation, an increase in sweat produced and a reduction in electrolytes lost through sweating, increased skin blood flow, and an ability to perform work at a lower core temperature and heart rate. 

It is VERY important to remember that acclimatization takes time, and much more time than we would generally expect. Typically it can take 7-14 days, so if we are planning on taking a vacation our bodies will NOT have time to acclimatize. If we look at workplace fact sheet supplied by NIOSH (https://www.cdc.gov/niosh/mining/userfiles/works/pdfs/2017-124.pdf), by the 5th day the employee should be able to work a full normal shift. However, they say they will still not be fully acclimatized, see productivity improvement for another week.

If you had a heat related illness once, it is more likely to occur again. This is because you may have some underlying unknown risk factor or due to the after effects of your previous heat related illness. As we mentioned last week, heat related illness can cause damage to our  organs, hurting their efficiency and making another heat related illness event more likely.

A less discussed by extremely important factor regarding the heat are any medications you are on. All drugs change your physiological or mental state.  In most cases these changes have an adverse effect on how your body copes with excess heat. A common recreational example is alcohol.  Alcohol is known to increase urine output and cause dehydration which greatly increases our  risk of heat related illness. But wait a minute you say, every couple of years a study pops up on my news feed touting the benefits of beer after exercise! How can this be? As with anything the devil is in the details. A single low alcohol beer (less than 4% abv) has no noticeable dehydration effects and can provide your body with other added nutrients.  However, if you have more than just one, or consume  beer with more alcohol (most sold in the United States  have a higher than 4% ABV) you are putting yourself at risk.

A significant number of medications, many of which are over the counter, can reduce your tolerance to the heat. Rarely is this side effect mentioned prominently. They act on the part of the brain that controls the skin’s ability to sweat, here is a quick non-exhaustive list:

• Antihistamines: these are typically allergy medications including; Zyrtec, Benadryl, Allegra, Claritin, Xyzal, and Clarinex. Antihistamines work on an area of the brain that controls the sweating and reduce the amount you sweat. If you are using these medications consider evaporative cooling products in dry conditions and cooling vests in humid environments. We will be discussing a wide variety of cooling products in Part 6 of this series.

• Antidepressants: specifically SSDI’s like Prozac.  This drug may make you sweat more and thus be at greater risk of dehydration. Make sure to include extra water in your cooling plan.

• Phenothiazine: used as antipsychotics such as Abilify and Zyprexa limit the sweating mechanisms and possibly the brain's temperature regulation system.

• Anticholinergics: include a wide range of drugs that are used for Incontinence, COPD, Parkinson’s Disease and Asthma. The most common is used under the trade name Spiriva. These also impair your ability to sweat.

Beta blockers and ACE inhibitors also lower blood pressure which reduces the body's ability to expel heat and reduce the ability of the heart and lungs to adapt to hot weather. For a more complete list see the chart below:

These personal risk factors will lay the foundation of your individualized cooling plan that we will describe in a future installment of this blog series. As each of these risk factors affects your heat sensitivity in a different way, the plan to combat these factors will have different strategies. For example if I am taking Zyrtec for allergies I should be aware that it will  lower my sweat levels and if I live in a dry climate (like Arizona) a misting fan or evaporative cooling towel may be sufficient if I am otherwise young and in good health.  If I live in a more humid environment (like Georgia) these evaporative techniques will not be adequate and I should consider a cooling vest.

There is one last Personal Risk Factor we would like to address that is generally not brought up when  discussing the heat but seems to be a major factor when we look at the data of occurrences of heat related illness. 

According to the chart above, males are at a greater risk of heat related illness. So next time you or your loved one are working in the yard on a hot day, remember that and stay safe.

Putting it all together
As children from the 80s, we remember the coach yelling at us that we were weak because we asked for water during practice at temps in triple digits. Thank goodness the good old days are behind us, but our old macho attitudes are misguided and dangerous. Use this information to empower yourself and your body. As we have stated before there is ONLY prevention. Use your personal information to ask yourself,

How am I feeling?

Have I drank enough water?

Am I putting unnecessary stress on my heart?

What's my past experience tell me?

As we have learned there is no one-size-fits-all rule for the heat. It is upon each of us to be aware of our bodies and how they feel in relation to our age, gender, fitness level, medications, and possible diseases in relation to the heat and heat index. Heat is a multi-layered problem that must be dealt with seriously. Heat can literally kill you. But with knowledge and assessment, we reduce risk and even fight fatigue while being healthy and safe.

Stay Cool,

The ThermApparel Team

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ThermApparel is a small business making big waves in the heat sensitivity world by designing the first lightweight, comfortable and invisible cooling vest, UnderCool. Check us out online, on our blog, or on Facebook, Twitter, Pinterest, LinkedIn and Instagram.

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