Beat the Heat: Improve Your Heat Stress Tolerance

Sweltering summer heat may leave you feeling uncomfortable, exhausted, and seeking a source of cool air. Heat stress reduces your physical work capacity, work productivity, and increases the risk of occupational health challenges. It interferes with sleep quality, can stress your mood and far more. Hydration and electrolytes and several other factors support your ability to make it through the heat of summer. Learn how to support your heat stress tolerance!

How Your Body Manages Heat

Several remarkable processes occur in your body in response to heat and temperature challenges. When you feel hot or are in a hot environment, blood vessels dilate in your skin. This brings blood from muscles to the skin surface to help remove heat from your body. Sweating also occurs which helps remove body heat. Your brain regulates these mechanisms by temperature sensitive nerves, numerous neuroimmune chemicals, and cytokines.

While blood vessels dilate bringing blood to the skin, the cardiovascular system goes through significant fluid shifts to maintain blood pressure for the rest of your body. These mechanisms are highly sensitive to your hydration status, electrolytes, overall health, and many other factors.

Factors That Affect Heat Stress Tolerance

Your tolerance to heat stress and to physically manage the above mechanisms is affected by many things. These include age (infants, children, and elderly), being overweight, poor physical fitness, dehydration, lack of sleep, and lack of acclimatization to heat.

Other factors that make heat stress more challenging are diabetes, viral infections or illness with fevers, cardiovascular disease, autonomic nervous system or some endocrine disorders, or other causes of frail health. Vaccination within past 48 hours, current sunburn or burns, illicit drug use, tobacco use, previous day heat stress, air travel, and inflammatory disorders are other contributing factors to decreased heat stress tolerance.

Additional Physical Effects

Heat stress affects your antioxidant levels and functionality. It causes reduced antioxidant capacity and lower glutathione levels in the blood. Heat stress also leads to increased tissue damage to lipids or lipid peroxidation. Cooler environmental temperatures, however, stimulate antioxidant defenses in the blood.

Prolonged heat exposure is a significant physiological stressor if you work/play in the heat of the day. Prolonged heat stress contributes to increased intestinal permeability. It also leads to an increase of toxins and cytokines released into circulation.

Prolonged heat stress provokes wear-and-tear on the liver, immune system, and blood flow. It can lead to very significant stress on your brain and kidneys. Significant and prolonged heat stress can also cause DNA damage. It increases oxidative stress from ROS free radicals and injures mitochondria. Heat stress can progress to heat illness, heat cramps, heat exhaustion, sun stroke, heat stroke, and death.

Medications and Heat Stress

Numerous medications also affect your ability to manage heat stress. Drugs such as ACE inhibitors may interfere with your sense or perception of thirst. Some medications such as opioids, SSRIs/serotonin reuptake inhibitors, tricyclic antidepressants, anti-cholinergics, and carbamazepine affect how your brain manages heat stress. In addition, anti-cholinergics, tricyclic anti-depressants, and antipsychotics can impair neurological mechanisms necessary for sweating.

Stimulants or sympathomimetic medications which increase heart rate, force of heart contraction, and blood pressure cause your blood vessels to constrict rather than dilate. This adversely affects the regulation of blood flow to the skin and sweating mechanisms.

Furthermore, medications that impair attention and alertness may make it harder for you to recognize changes in your health. Because blood flow changes to your internal organs, heat stress may even affect how well medications work in your body.

Physical Fitness and Body Weight

Physical fitness and body weight affects heat stress tolerance even in young individuals. A recent study evaluated US Army recruits with heat stress, body weight, and physical fitness. Compared to trained normal body weight recruits, untrained, normal body weight recruits had twice the risk of heat illness. Trained overweight recruits had nearly 4 times risk and untrained, overweight recruits were almost 8 times more likely to become ill from heat.

Hydration

The most important dietary thing that you can do to help your body is to drink adequate water, but not excessive water intake. Your tolerance to heat declines as you become dehydrated. Fluid depletion causes sweating to stop. It also causes reduced blood flow to the skin, so your muscles and internal organs retain the heat. Even when you are acclimated to the heat, loss of hydration affects your heat tolerance. Hydration is critical for the primary mechanisms in your body to manage heat stress.

The general rule of thumb for basic adequate hydration is to drink one half of your body weight in ounces of water. For example, if you weigh 150 pounds, then you need at least 75 ounces of water or fluids daily. Coffee, pop, alcohol, heavily caffeinated beverages, or thick beverages like a protein smoothie, kefir, etc. are generally not counted for basic hydration.

Hydration recommendations change if you participate in athletic activities. Shortly before exercise, it is recommended to drink at least 250-500 ml (8.5 -17 ounces) of water. During endurance exercise or training, a general recommendation is to ingest 200-250 ml water/6-8% carb/electrolyte mix every 15-20 minutes. Once you are done exercising, it is still vital to continue replacing fluids as you are still losing fluids after exercise stops. A simple way of checking hydration status is to watch your urine output. With adequate hydration, urine should be a clear or pale yellow with sufficient volume. Darker hues of yellow or amber, especially in scanty amounts clearly indicate significant dehydration concerns.

For workers in hot environments, the recommended rate of rehydration is somewhat similar to athletes. If temperatures are below 113 degrees F, drink 250 ml or 8.5 ounces every 30 minutes. It is important to note that sodium loss in sweat varies greatly and is not significantly related to sweat rate.

Electrolytes

Hydration also affects how electrolytes (calcium, magnesium, potassium, sodium, chloride) work in your tissues. Many individuals fail to consume adequate magnesium and potassium in their diet. Several medications also deplete electrolytes from your body. This makes you more prone to muscle cramps and even less tolerant to heat. Muscle cramps with heat stress can also occur because your brain and nerves are stressed.

In addition, individuals often remove added salt/sodium chloride from their diet to lower blood pressure numbers. Heat stress and excess water consumption often increases your salt needs. Symptoms may or may not occur with excess water and inadequate salt, but low sodium levels in your body during heat stress can progress to serious health changes. Salt is needed by your body.

Diet quality, kidney and cardiovascular function, and medications amongst other factors affect your electrolyte status and hydration needs. Hydration status affects your cardiovascular stability and decreases stress responses to the intestinal lining, brain, and kidneys.

If you feel thirsty or have lost more than 2% of your body weight, you are already dehydrated. Dehydration increases oxidative stress and reduces your antioxidant defense activity. Rehydration reduces free radical stress and improves antioxidant defenses.

Things to Mindful About

Energy and electrolyte drinks are enormously popular. They may be your preferred beverage during the heat of summer. Be aware as they may not be as healthy as they are advertised to be. These beverages often contain substantial amounts of caffeine and sugar that further stress cardiovascular health. Caffeine causes vasoconstriction which interferes with your body’s natural cooling mechanisms. These beverages can also make you more prone to dental cavities.

It’s tempting during the summer to have lots of cold, sugary treats. However, studies show that consumption of fructose rich beverages may increase the likelihood of kidney stones in individuals suffering from heat stress. Table sugar and high fructose corn syrup are common sources of fructose. Be mindful about reading the food labels. Reduce or avoid foods and beverages with added sugar and fructose. Choose healthier options when available.

A cold beer also may hit the spot, but alcohol prior to heat stress can increase intestinal permeability. It also acts as a diuretic which can increase dehydration. Make sure you keep up your water intake with that cold brew!

Heat Stress and Nutrients

Athletes or individuals that work outdoors in high heat environments may find a few nutrients helpful to manage heat stress effects on the intestinal lining.

Glutamine, a conditionally essential amino acid, used prior to an athletic event has been found helpful in maintaining intestinal barrier integrity against heat stress. TNF-alpha, NF-kappa B, and endotoxins were also found lower post-event in athletes when they used glutamine to support gut barrier integrity. Results found that glutamine intake several hours prior to the activity was more helpful.

Another randomized, controlled clinical trial found that athletes who consumed collagen peptides before and after an athletic event with heat stress experienced less LPS toxins released into circulation compared to the control group.

Turmeric also provides dietary protection to the gastrointestinal barrier during exertion related heat stress. A clinical trial demonstrated that use of turmeric/curcumin at 500 mg/day for three days prior to athletic events protected gastrointestinal barrier integrity and cytokine release from heat stress. Turmeric, resveratrol, and many other plant-based nutrients provide antioxidant protection to mitochondria, cardiovascular tissues, and your brain to help modulate the effects of oxidative heat stress.

Researchers have found that there are some nutrients or dietary patterns that may worsen heat tolerance during prolonged heat stress and physical/athletic activity. These include caffeine, beet root, arginine, extended or intermittent fasting or “train-low” or “glycogen depleted training.”

Everyone has a different level of heat tolerance. Be sensitive to your needs and those around you. Keep watch on those who are most vulnerable and enjoy your summer!

Additional resources may be found at:

Magnesium Depleted by Numerous Drugs

Potassium – A Valuable Mineral for Health

Potassium Balances Salt Intake

To Salt or Not to Salt – That is the Question

Glutamine: Critical for Gut, Immune System, and Muscles during Stress and Aging

Common Medications That Rob the Body of Nutrients

Summertime Nutritional Tips for Sun, Fun, and Bumps that Go With Them

Exercise Endurance and Energy Linked to Gut Health