Heat Related Illnesses

Introduction

Competing in the heat can take its toll, and heat related illnesses are very common (Dr. Stoddard's note - I have lost count of the many individuals I have had to help in the medical tent at endurance events held in the heat!). Symptoms can range from simple thirst, headache, nausea and cramping all the way to dizziness, coma and even death. Everyone is at risk! Most at risk, however, are individuals who are not acclimatized to the heat. Many people train inside, sheltered from the heat. Alternatively, they train outside, but early or late in the day, when the ambient temperature is lowest. However, many events and competitions occur during peak sunlight, when heat is maximum, so athletes are not prepared for the battle against daytime heat. Compound this with some sports requiring use of equipment such as helmets, which contribute to heat retention, and you have a recipe for heat related illnesses.

Your Enemies

Simply put, you have four enemies when you are training or competing in the heat:

1. Dehydration
2. Electrolyte Depletion
3. Hypoglycemia (Low Blood Sugar)
4. Lactic Acid Accumulation

The following is a summary of common heat illnesses. In reality, there are many overlapping features of all of these illnesses, and an athlete may experience combinations of the various symptoms mentioned.

Heat Cramps

Cramping may occur in muscles that are used repetitively during an athletic event. For example, runners often get cramps in their thigh muscles or calf muscles; tennis players may cramp in forearm muscles ⁽³⁰⁾. This syndrome results from a variety of heat related imbalances that alter the way in which muscles contract. While muscle contraction is an incredibly complex physiological phenomenon, normal contraction requires all of the following:

1. Normal hydration (water balance)
2. Normal electrolyte balance (Sodium, Potassium, Calcium and Magnesium)
3. Normal blood sugar (carbohydrate balance)
4. Controlled lactic acid production and neutralization

All of these factors work synergistically to promote normal muscle contraction, and as more of these factors become abnormal, your chance of cramping goes up.

Water is often advocated as a good drink for rehydration in the heat, but it isn't. It contains no electrolytes, no lactic acid buffer and obviously contains no carbohydrates. Therefore, drinking only water increases one's chances of succumbing to heat illness, especially the longer you go. For these reasons, water is very overrated as a "sports drink", and while better than nothing, falls far short of supplying the active person with essential support for performing while sweating!!

And while some sports drinks offer adequate amounts of carbohydrate (a 5-6% solution, or 50-60 grams/liter, is recommended), some have too much carbohydrate, causing gastrointestinal upset.

Probably the most important contributor to heat cramps, however, is electrolyte depletion and hypotonic (low electrolyte) fluid replacement ⁽³¹⁾. Virtually all existing sports drinks fall very short on the electrolyte end, being not much better than water!! Human sweat typically contains much more sodium and potassium than does the typical sports drink. Most current sports drinks offer 1/6-1/2 of the appropriate amount of these electrolytes. e load™ has finally addressed this important issue, containing physiological levels of sodium, potassium, calcium, magesium and zinc.

Finally, lactic acid build-up in your blood can also contribute to cramping, and ingredients like MultiCitrate™, once converted to bicarbonate in the body, can help neutralize this build-up ⁽⁹⁾.

Heat Exhaustion

Heat exhaustion is a condition resulting from the same four problems mentioned under heat cramps, namely dehydration, electrolyte depletion, low blood sugar levels and lactic acid build-up. This syndrome results in increased thirst, nausea, headaches and dizziness ^{(31, 32)}. The individual is still able to sweat, however, which aids in cooling the body down. Contrast this to ...

Heat Stroke

... which is everything heat exhaustion is, but has the added feature of reduced, impaired or absent sweating (not a good thing, as this is the only way your body can lower its temperature). This results in very high internal (body core) temperatures, a very dangerous situation. This potentially leads to loss of consciousness, coma and even death. Permanent damage to the hypothalamus, an area of the brain responsible for controlling our internal temperature, can also result. Once damaged in this way, a person is at higher risk for future heat related illnesses ^{(31, 32)}.

Hyponatremia

Hyponatremia, or reduced blood sodium concentrations, has been recognized as one of the most concerning potential health hazards of sporting events performed in the heat. This condition has been reported in marathons, triathlons (up to 20% of Ironman participants), and other ultraendurance events ⁽³³⁾, and probably occurs in many other sports as well. It usually happens during longer events performed in hotter temperatures, and especially so when combined with the one-two punch of heat and humidity. However, this problem may occur even in shorter events in susceptible individuals.

Sodium vs. Salt

Sodium is one component of salt (table salt). Salt, or sodium chloride, contains 1 part sodium to 1.5 parts chlorine. Your sweat on average contains anywhere from about 1.75 grams of salt (700 mg sodium plus 1050 mg chlorine) to 3 grams of salt (1200 mg of sodium plus 1800 mg chlorine) per liter. If you sweat an average of one liter per hour, you lose anywhere from 1.75-3 grams of salt per hour. Since a teaspoon of salt contains about 6 grams, this equals about 1/4-1/2 teaspoons of salt lost. Some might not think this seems like a whole lot, but if you consider that a 140 lb person only has about 40 grams (almost 7 teaspoons) of salt in his/her blood to begin with, you start to get a feel for how significant these losses can be when multiplied over several hours!

According to one of the most respected textbooks in medicine, and a definite authority on the topic, relative to sweat, "these losses are almost entirely replaced by ... solutions (including Gatorade*) that have a much lower salt content. The net effect is water retention and, in some cases, symptomatic hyponatremia, with a fall in plasma sodium concentration .…" ⁽⁸⁾

* direct quote from reference #8

Definition

Hyponatremia is defined as a blood sodium concentration of < 135 mEq/liter (< 3.10 g/liter), with normal ranges usually falling between 138-142 mEq/liter (3.17-3.27 g/liter). In the most severe cases, blood sodium concentration may fall to below 120 mEq/liter (2.76 g/liter), a true medical emergency! As can be seen with these numbers, there is not much difference between normal and an emergency situation (about .50 g of sodium/liter, or 1/12 teaspoon/liter!).

Symptoms of hyponatremia include nausea, muscular cramping, stomach upset, vomiting, dizziness, seizures and delirium. Coma and even death may result, and has been reported in several cases.

Torn Between Two Ideals

Our bodies have many built in survival mechanisms that function without our conscious awareness or direction. Two important functions related to successful completion of races in the heat and humidity are maintenance of both hydration and normonatremia (normal blood sodium levels). Unfortunately, these functions are often in competition with each other.

Dehydration is not uncommon in the heat, and can cause a drop in our blood pressure ⁽³⁴⁾. When dehydrated, pressure sensitive receptors located in our carotid arteries, called baroreceptors, sense a drop in our blood pressure. This in turn sets off a variety of counter measures, one of which is the release of Antidiuretic Hormone (ADH) from the pituitary gland in our brains, which tells the kidneys to conserve water, making our urine more concentrated, and reducing urination. Some triathletes experience "shutdown" in their ability to urinate during Ironman races, and this mechanism likely plays a major role in this phenomenon. The net effect is an increase in hydration and blood pressure. Unfortunately, this extra water reabsorbed by the kidneys also contributes to hyponatremia.

Hyponatremia, on the other hand, has the opposite effect in that this condition leads to reductions in the release of ADH, thus allowing the kidneys to excrete more water, making our urine more dilute, and increasing urination ⁽³⁵⁾. Urinating more water will result in an increase in sodium concentration in the blood. Unfortunately, the loss of this water leads to further reductions in blood pressure. Some triathletes experience increases in urination of especially dilute urine after an Ironman, which is the body's way of correcting a hyponatremia that evolved during the race.

Therefore, two competing physiological processes are trying to maintain an optimum internal environment-one corrective process improves dehydration, but potentially makes hyponatremia worse, while the opposite occurs when trying to improve hyponatremia. So, which process wins when both are competing?

This is a complex question, and one that still has no firm answer. Research is ongoing, however. Suffice it to say, it is probable that dehydration plays a more significant role in stimulating protective responses, which may have a role in perpetuating hyponatremia.

How to Prevent this Dilemma?

One principle of human physiology and medicine that is used as a "prime directive" is "for optimum health, replace what is lost at the rate of loss". Some examples of this are:

1. You lose protein on a daily basis in the form of shed hair, nails, intestinal losses and skin. This amount must be replaced daily with dietary protein, at the same rate of loss, for optimal health.
2. In an average non-exercising day with comfortable temperatures, you typically lose about 1/2 liter of water in the form of sweat and respiratory losses. This must be replaced at the same rate to avoid dehydration.
3. If your daily energy expenditure is 2000 Calories, and assuming you neither want to gain nor lose any weight, you must eat 2000 Calories per day to balance your losses.

I could go on - there are hundreds of examples applicable to the human body. This same principle should be applied to your training and racing diet in general, and definitely should be applied to water and sodium balance. As mentioned earlier, your sweat may contain anywhere from 700-1200 mg of sodium (1.75-3 grams of salt) per liter. Losing about 1 liter an hour means you need to replace both the water component of 1 liter and the sodium component of 700-1200 mg, per hour! If you strive to replace your water and sodium losses at the rate of loss, your odds of developing hyponatremia and dehydration will be drastically reduced! This is facilitated if you consider these two needs as totally separate. You must understand what your water requirements and your sodium requirements are, and ingest adequate amounts of each.

Example

Based on before and after weights of many training sessions, Scott knows that he loses about 1 liter of sweat per hour in conditions predicted for the upcoming Ironman. He also knows that his sweat is usually quite concentrated, leaving a lot of salt stains on his clothing. He guesses his sweat contains sodium at the higher end of the normal range, about 1200 mg/liter, so with a sweat rate of 1 liter per hour, ideally he should replace 1200 mg of sodium per hour. Scott's favorite sports drink contains only 300 mg of sodium per liter. Each gel he is consuming contains 50 mg of sodium, and each bar he consumes contains 100 mg of sodium. The following table summarizes Scott's water and sodium intake per hour:

Based on this basic Ironman diet, Scott ingests enough water every hour, but his sodium intake is far below what he actually needs, about 650 mg per hour short, considering he needs 1200 mg/hour. Multiply this by 12 hours, and you have 7.8 grams of sodium, or 19.5 grams of salt! Most likely, Scott is headed for severe hyponatremia.

Scott can do several things to bump up his sodium intake:

1. Choose a sports drink that supplies more sodium. He cannot simply drink more of the same drink, as he only needs one liter of water per hour, and drinking more, even though it will increase his sodium intake, also increases his water intake. This will throw his water balance off, resulting in overhydration (see below) and risking hyponatremia!
2. Increase ingestion of other foods that contain sodium.
3. Use salt tablets/capsules. For example, let's say that Scott used a capsule containing 45 mg of sodium per capsule. He would therefore need about 14 capsules (630 mg) per hour to balance sodium losses.

Overhydrating

A lot of talk about "overhydration" has been occurring of late. The thought that one could actually drink too much is probably inconceivable to many.

It is important to note that even if you are just matching your sweat rate with a low sodium fluid, you may still develop hyponatremia ⁽¹⁷⁾. Failing to match the rate of sodium loss, and replacing relatively too much water can lead hyponatremia. This problem cannot occur if you are balancing your sodium intake with losses, as illustrated above.

In conclusion, hyponatremia is a relatively common occurrence in ultra endurance events like the Ironman, and is probably underreported in other sporting events. Using the strategy of separating water from sodium ingestion to figure out needs, and replacing each as they are lost, your risk of developing hyponatremia will be drastically reduced.

Back to the basics - water balance, electrolyte balance, carbohydrate balance and neutralization of excess of lactic acid production. Keep all of these in check, and your risk for all of the above will be drastically reduced!

Prevention of Heat Related Illnesses

Want to compete in the heat without needing medical attention? The following is a crash course in handling the heat:

1. Train in the heat

You must acclimate your body to hot/humid weather conditions. Too many athletes train in favorable weather conditions, and never teach their bodies to perform in the heat. Gradually increase the amount of training you do at hotter times of the day.

Additional Note: Remember your sun block, with minimum SPF 30!

2. Practice drinking (and eating)

Pick your fluid, and stick to it (e load™ would be a good one!). You must practice drinking (and eating, depending on your event) during times of physical stress and exhaustion in order to train your gastrointestinal tract to tolerate and absorb what you are ingesting. Optimal digestion requires adequate gut blood flow, adequate hydration, normal electrolyte levels, normal blood sugar (carbohydrate) levels and adequate neutralization of excess lactic acid levels (sound familiar?). Exercising in the heat can be very hard on your gut because blood flow is diverted to your muscles (for muscle contraction) and skin (for sweating and heat control). Add to this dehydration, electrolyte depletion, carbohydrate depletion and lactic acid build-up, and you have a great recipe for developing that uncomfortable bloated feeling, when you feel that your gut has "shut down", and everything you eat or drink seems to stay stuck in your stomach! Also, your stomach works best when it is at least 1/2 full, so always maintaining some fluid and/or food in your stomach is very important.

3. Allow sweat to evaporate - minimize wiping it away

We sweat to cool us down. Once sweat is on our skin, it must evaporate if it is going to reduce our body core temperature. The process of evaporation requires energy - heat energy, to be exact. This heat energy is taken from our bodies. Therefore, the more sweat we allow to evaporate, the better off we will be. However, if it is too humid out, you will have trouble evaporating your sweat. As much as possible, however, minimize wiping away sweat, unless you are cold!

4. Wear a hat with a rim and a mesh top

Protect your head and face from external heating from the sun.

5. Provide frequent, cool water dumps and hose downs for your head and body if you can!

This will help reduce your body temperature. However, this does not replace the need to drink!