Tuesday, May 31, 2011

Heat Stroke and Hyponatremia

The most likely cause of death during hot weather sports is heat stroke, when the body temperature rises so high that it cooks the brain (Medicine and Science in Sports and Exercise, July 2008). Nobody should ever die of heat stroke because your body sends you warning signals as your temperature rises. Those most likely to suffer heat stroke are those who have arteriosclerosis, are overweight or are in poor shape. The treatment for a person who collapses from heat stroke is immediate immersion in cold water.

In 1965, I almost died from heat stroke in an unimportant local race in Arlington, Virginia. I am still embarrassed by the stupidity that I showed when I ignored all of the warning signs as my temperature continued to climb.

Signs of impending heat stroke
First your muscles are affected, then your circulation and then your brain. As your temperature starts to rise, your muscles feel like a hot poker is pressing against them.

It is normal for intense exercise to make your muscles burn, but hard exercise does not cause painful burning that feels like fire. Furthermore, the burning of hard exercise is relieved by slowing down. The muscle burning of impending heat stroke does not go away when you slow down.

As your temperature rises further, the air that you breathe feels like it's coming from a furnace and no matter how rapidly and deeply you try to breathe, you can't take in enough air. When you exercise intensely, you can become very short of breath, but the air you breathe will not burn your lungs. Burning in your lungs, not relieved by slowing down, signals impending heat stroke.

When you feel that the air is so hot that it burns your lungs, stop exercising. This sign means that your heart cannot pump enough blood from your exercising muscles to your skin, so heat is accumulating rapidly and your temperature is rising rapidly. Your temperature is now over 104 and continuing to exercise will raise your body temperature even further and it will start to cook your brain.

Your head will start to hurt, you'll hear a ringing in your ears, you may feel dizzy, you may have difficulty seeing and then you will end up unconscious. Your temperature is now over 106 and your brain is being cooked just as the colorless portion of an egg turns white when it hits the griddle.

When does heat stroke occur?
Almost all cases of heat stroke occur when you suddenly increase the intensity of your exercise, such as the finishing sprint of a long distance running or cycling race, or an intense run down the field in soccer.

How body temperature can rise uncontrollably
An excessive rise in body temperature is caused either by producing too much heat or by inability to dissipate the extra heat. When you exercise, almost 80 percent of the energy that is used to drive your muscles is lost as heat. That means that the harder you exercise, the more heat you produce.

During exercise, more than 70 percent of the energy used to drive your muscles is lost as heat. Your heart has to pump extra blood from your hot muscles to your skin where you sweat. Sweat evaporates and cools your skin to dissipate the heat. The harder you exercise, the more heat your muscles produce. Everyone who exercises, particularly in hot weather, has to sweat to keep the body temperature from rising too high.

Drugs can cause heat stroke
Heat stroke is more likely to be caused by inability to get rid of heat than by producing too much heat. Stimulants such as amphetamines or cocaine can kill athletes by preventing them from getting rid of heat by blocking sweating and blood flow to the skin. A single nasal dose of cocaine can block blood flow to the skin and sweating, to prevent a person from cooling his own body (Annals of Internal Medicine, June 4, 2002).

Treatment
When a person passes out from heatstroke, get medical help immediately. Any delay in cooling can kill him. Carry the victim rapidly into the shade and place him on his back with his head down and feet up so blood can circulate to his brain. Cool him by pouring on him any liquids you can find or spray him with a hose. It doesn't make any difference what you pour on him: milk, Coca Cola, beer, or anything else. Evaporation of any liquid cools. As you cool him, he will then wake up and talk to you and act like nothing has happened. While he's sitting or lying there, his temperature can rise again and he can go into convulsions or pass out again, so he must be watched for at least an hour.

An athlete or exerciser who passes out from overheating should be immersed in cold water immediately to prevent brain and multiple organ damage. However, a heart attack can also cause a person to pass out and this should not be treated with cold water immersion. Therefore always get medical help immediately when you see a person pass out during exercise.

Prevention
Heat stroke is caused by continuing to exercise intensely in spite of all the warning signals that the body presents. Dehydration also increases your risk for heat stroke.

When you compete in sports, you need to drink before you feel thirsty, because you slow down and lose power long before you have any signals to tell you that you are dehydrated. In warm weather, trail runners raced 12 km (7.2 miles) much faster when they took fluids (Journal of Athletic Training, March-April 2010). With fluids, they averaged 53.1 minutes compared to 55.7 minutes without fluids. Immediately after the race, the dehydrated runners had signs of greater body stress such as heart rates six beats per minute faster and intestinal temperatures .22 degrees C higher.

Thirst is a late sign of dehydration
You won't feel thirsty during exercise until you have lost between two and four pints, or two to four pounds. Thirst is a very late sign of dehydration. You sweat during exercise, and since sweat contains much less salt than your blood, you lose far more water than salt during exercise. As blood salt levels rise higher and higher, they trip off special osmoreceptors in your brain to tell you that you are thirsty. Since it takes a long time for blood salt levels to rise high enough to tell you that you are thirsty, you will be severely dehydrated long before you feel thirst.

You need more sugar in hot weather
During long sports competitions, you need to take sugar as well as fluid because running out of sugar stored in muscles slows you down. The only mineral that you need to replace during exercise is common table salt. Water or your favorite drink plus food containing sugar and salt are just as effective as any sports drink to maintain endurance and prevent heat exhaustion. The best exercise drink is the one that tastes best to you, because that's what you will drink the most (International Journal of Sport Nutrition and Exercise Metabolism, January 2002).

Hyponatremia
Up to fifteen years ago, athletes were advised to drink as much as they could to insure that they did not lose any weight during endurance competitions. This caused a condition called HYPONATREMIA which has killed some novice cyclists, runners and athletes in other endurance sports. It occurs almost never in trained athletes because it is most likely to occur in people who slow down so much that they spend too much time drinking fluids and too little effort maintaining pace. During competitions, you work so hard to maintain pace that you have to conscientiously work just to drink enough.

How hyponatremia kills
Hyponatremia is caused by drinking too much fluid, not by excessive loss of salt in sweat or by the stress of exercising. The extra fluid expands blood volume and dilutes blood salt levels. This causes blood salt levels to drop too low, while brain salt levels remain normal. Fluid moves from an area of low salt concentration into areas with high salt levels, so fluid moves from the bloodstream into the brain, causing brain swelling. Since the brain is enclosed in the skull, which is a tight box, the brain expands and has nowhere to go, so it is squashed to cause headache, nausea, and blurred vision.

Blood tests only way to diagnose hyponatremia
Since the symptoms of hyponatremia are the same as those caused by pure dehydration with normal blood salt levels, the only way to diagnose the condition is with blood tests. As blood salt levels drop even lower, the person becomes confused, develops seizures and falls unconscious. You should suspect hyponatremia when the event takes more than four hours and the athlete has been drinking often during the event. Anyone who is confused, passes out or has seizures should be sent to a hospital immediately. Hyponatremia requires skilled management because the first impulse of an inexperienced physician is to give intravenous fluids, which dilute blood salt levels further, causing more brain swelling that can kill the patient.

How much fluid should you drink?
You will not become thirsty during exercise until you have lost between two and four pints of fluid, so you can't wait for thirst to encourage you to drink. Dehydration makes you tired and it is unlikely that you can replace the lost fluid during a race after you have become thirsty. The American College of Sports Medicine recommends a limit of 1200cc (5 cups, 2.5 pints, a little over 1 quart, or 2 average size water bottles) per hour, but for a person who is not exercising near his or her maximum, this could be too much (Clinical Journal of Sport Medicine, July-August 2005). A person exercising near his capacity and not slowed down by fatigue probably does not have to worry about limiting fluid intake. He is working so hard to maintain intensity that he doesn't have enough time to drink too much. On the other hand, people slowed down by fatigue or those who are out of shape should limit fluid intake, probably to less than two water bottles per hour.

Drink to avoid thirst
No studies show that forced drinking of fluids is any more effective than just drinking frequently to avoid thirst (Annals of Nutrition and Metabolism, November 2010). So current advice is to drink frequently, but just try to avoid feeling thirsty. You are in trouble with dehydration when you start to feel thirsty. Thirst is such a late sign of dehydration that once you feel thirsty, it is too late for you to catch up on your fluid needs during competition.

Friday, May 27, 2011

The Dangers of Fructose

An ever-increasing number of studies show that sugared drinks and foods cause fatty liver, obesity, high blood pressure, diabetes, heart attacks, kidney damage and premature death. A review of recent studies shows that fructose may be more damaging than other sugars (Journal of the American Society of Nephrology, November 29, 2010).

Fructose is found in:
• fruit juices (sucrose, which is glucose and fructose bound together in a single molecule),
• table sugar from sugar cane and beets (sucrose),
• honey (mostly glucose and fructose separate from each other), and
• drinks and foods that contain High Fructose Corn Syrup (glucose and fructose, separate from each other).
• Sucrose is also found in most fruits and many vegetables.

Sucrose contains 50 percent fructose and 50 percent glucose bound together. High Fructose Corn Syrup contains approximately a 55/45 proportion of fructose and glucose. As far as the body is concerned, the ratio of glucose to fructose is not important. The issue is whether fructose is more harmful than glucose.

Glucose, but not fructose, can circulate in your bloodstream
Only single sugars can pass from your intestines into your bloodstream. The double sugars, such as sucrose in fruits or lactose in milk, have to be broken down into single sugars before they can be absorbed. Glucose is the only sugar that is allowed to circulate through your body. Fructose cannot circulate in your bloodstream. Fructose is absorbed from your intestines into the blood vessels that carry blood to your liver, where it is immediately converted to glycogen, the stored sugar in your liver, or to triglycerides, a type of fat.

When the liver's stores of glycogen are needed for energy, the glycogen is converted into glucose and released into the bloodstream. After glucose is absorbed into the bloodstream, it passes into your general circulation and is used for energy for your brain, muscles and other tissues. Glucose in your blood supplies almost 98 percent of the calories necessary for your brain to function, which is why a sudden drop in blood sugar can cause you to pass out.

How fructose causes liver damage, obesity, diabetes and death
Your liver converts excess fructose into triglycerides.
Triglycerides:
• are building blocks for the bad LDL cholesterol that forms plaques in arteries,
• can be stored in your liver to cause a fatty liver,
• can be stored in your fat cells to make you obese.

Having excess triglycerides in your liver:
• causes a condition called fatty liver which interferes with normal liver function; and
• causes fat to be stored in your belly and decreases insulin sensitivity to cause diabetes (Journal of Clinical Investigation, May 2009).

Triglycerides can pass into your bloodstream to:
• damage your kidneys to cause high blood pressure, and
• in very high amounts, can form clots in your bloodstream.

All of these side effects of excess triglycerides increase your risk for heart attacks and strokes.

Who is harmed by fructose?
Fructose appears to be safe if:
• You don't eat large amounts. You have to take in a lot of fructose to raise your triglycerides and become insulin insensitive. Small amounts will not harm you.

• You are not overweight. The fatter you are, the more likely you are to become diabetic. Full fat cells send out hormones of inflammation that block insulin receptors to increase risk for diabetes.

• You do not store fat primarily in your belly. Storing fat primarily in your belly means that you are already insulin insensitive and have high blood insulin and sugar levels. High levels of insulin cause fat to be stored specifically in the liver and belly.

• You exercise regularly. Contracting muscles draw sugar so rapidly from the bloodstream that there is less fructose available to be turned into triglycerides.

• You get your fructose from fruit, not fruit juice. Fructose in fruit is absorbed far more slowly than fructose in fruit juice. The fiber in fruit can keep fruit in your stomach for up to five hours and markedly slows absorption to reduce blood sugar levels. On the other hand, the sugar in fruit juice passes directly into the intestines to be absorbed immediately and cause a high rise in blood sugar. A high rise in blood sugar causes sugar to stick to cell membranes that causes irreversible damage.

Fructose helps athletes and exercisers
Fructose can be an athlete's best friend. When you exercise, your muscles and brain constantly draw sugar from your bloodstream as a source of energy. The energy for your brain is supplied by sugar in your bloodstream. There is only enough sugar in your bloodstream to last 3 minutes. So your liver has to constantly release sugar from its cells into your bloodstream. However, there is only enough sugar in your liver to last 12 hours at rest, and far less than that during exercise. Your liver can run out of its stored sugar and your blood sugar level can drop, you feel dizzy, lose all muscle strength and can pass out and suffer seizures. Cyclists call this "bonking." Bonking is common in bicycle racers who do not eat frequently during long races, but it is rare in long distance runners. When you run, your leg muscles are damaged from the constant pounding on the roads and you must slow down. However, you pedal in a smooth rotary motion which does not damage your muscles, so you can continue to pedal at a rapid cadence for many hours, until you run out of sugar.

Fructose is the best and most efficient sugar to keep up liver glycogen during competition and to replenish liver stored after an intense workout (Medicine & Science in Sports & Exercise, March 2011). Bicycle racers who ingest drinks that contain fructose can replace lost liver glycogen four times as fast as those who take drinks containing only glucose.

Glucose plus fructose is better than just fructose
If you exercise for more than a couple hours, you can use up almost all of your (stored liver glycogen. Taking drinks that contain both fructose and glucose will keep you going far more efficiently than if you take only one of these sugars (International Journal of Sport Nutrition and Exercise Metabolism, April 2010; Scandinavian Journal of Medicine & Science in Sports, February 2010). Most bottled sports drinks and sugared soft drinks in North America are sweetened with high-fructose corn syrup, containing glucose and fructose in close to equal portions.

No fructose when you are not exercising
Loading with sugared drinks and foods is safe only for people exercising intensely for more than two hours at a time. Low intensity exercise or exercising for less than two hours will not protect you from the potential damage caused by sugared drinks.

How exercise prevents fatty liver and prolongs life
Any exercise that you do will help to protect you from the ravages of sugared foods and drinks. It is usually safe to take sugared drinks while you exercise because blood sugar levels rarely rise too high during exercise or for up to an hour afterward. Contracting muscles draw sugar so rapidly from the bloodstream that there is no sharp rise in blood sugar.

• Contracting muscles help to prevent the high rise in blood sugar that follows eating refined carbohydrates during rest (American Journal of Clinical Nutrition, July 2008).
• Unlike resting muscles, contracting muscles do not require insulin to move sugar inside their cells (Journal of Applied Physiology, July 2005).
• Contracting muscles remove sugar maximally from the bloodstream, without needing insulin, during & up to one hour after exercise. The effect tapers off to zero at about 17 hours (Journal of Applied Physiology, February 2010).

You should avoid sugared drinks at rest
I recommend that you avoid all sugared drinks (sugared sodas and fruit juices) and foods with added sugars except during vigorous exercise.

What to drink during sports that require intense exercise for more than an hour:
Drink any sugared drinks. Ordinary beverages containing both glucose and fructose are probably best; there is no need to seek out special sugars or sugar combinations.

Wednesday, May 11, 2011

Caffeine: Good When You Exercise, Bad When You Rest

Caffeine increases sugar absorption from the gut. Taking caffeine when you eat carbohydrate-containing foods can double your rise in blood sugar (Journal of Caffeine Research, April 16, 2011). Since more than 35 percent of North Americans will become diabetic and have high rises in blood sugar levels after meals, most people should not take caffeinated drinks with meals that contain carbohydrates: bread, spaghetti, or sugared foods and drinks. If you are already diabetic, your blood sugar levels rise even higher and you suffer cell damage. A high rise in blood sugar causes all the horrible side effects of diabetes: blindness, deafness, heart attacks, strokes and so forth. However, during exercise, caffeine can increase endurance (Medicine & Science in Sports & Exercise, July, 2010) by increasing the absorption of sugar from your intestines and by increasing the uptake of sugar by your exercising muscles by as much as 26 percent (Journal of Applied Physiology, June 2006). Caffeine is found in coffee, tea, chocolate, and cocoa.

Sugared drinks cause higher rises in blood sugar than sugared foods.
No solid food is allowed to pass into your intestines. After food enters your stomach, the pyloric sphincter closes. Food is kept in the stomach until it is turned into a liquid soup. Then the stomach muscles squeeze the soup through the pyloric sphincter into the intestines. An orange can be kept in your stomach for up to five hours before it passes into your intestines. Since fruit juice is a liquid, it passes into your intestines immediately. So orange juice causes an immediate high rise in blood sugar, while an orange does not. Studies show that fruits decrease diabetes risk, while fruit juices increase risk (Diabetes Care, July 2008).

Caffeine drives blood sugar levels even higher.
Adding caffeine to sugar in a drink causes blood sugar levels to rise even higher than drinks that have only sugar.

Fruit juice is as damaging as high fructose corn syrup or table sugar.
High Fructose Corn Syrup (HFCS) has been blamed for the ever-increasing rates of obesity and diabetes in North America over the last forty years. However, HFCS appears to be no more damaging than fruit juice or drinks sweetened with table sugar. Most soft drinks are sweetened with HFCS. Both HFCS and conventional sugar (sucrose) contain a mixture of two sugars, glucose and fructose, in nearly the same concentrations: HFCS has 55 percent fructose/42 percent glucose, while sucrose is a 50/50 mixture. These numbers are so close that most researchers feel that the slight increase in the concentration of fructose is not important enough to cause disease in itself. The fructose in orange juice, table sugar and HFCS are equally damaging to your health.

How fructose harms:
Fructose is far more damaging to the liver than glucose and is thought by many physicians to be the main cause of the fatty liver that causes insulin insensitivity and type II diabetes. When your blood sugar rises too high, the pancreas releases large amounts of insulin. Insulin converts sugar to triglycerides. Since high levels of blood triglycerides increase risk for clots, your good HDL cholesterol carries the triglycerides from your blood to your liver to fill up the liver with fat to cause a fatty liver. Fructose causes far higher blood and liver levels of triglycerides than glucose does, so fructose is a more potent cause of a fatty liver. Having a fatty liver prevents the body from responding to insulin and blood sugar levels rise to increase diabetes risk.

During exercise, muscles protect you.
Resting muscles are inactive. They need insulin to remove sugar from your bloodstream. On the other hand, contracting muscles can remove sugar from your bloodstream without even needing insulin (American Journal of Clinical Nutrition, July 2008). The maximum effect is during exercise and continues maximally for up to one hour afterward and disappears at around 17 hours (Journal of Applied Physiology, February 2010).

How caffeine and sugar help you during exercise:
Caffeine increases endurance by helping the body use more sugar from drinks that you take during exercise (Journal of Applied Physiology, June, 2005). The limiting factor to how fast you can move over distance is the time it takes to get oxygen into muscles. Since sugar requires less oxygen than fat or protein do, muscles move faster with more power when they burn sugar. Those who took sugared drinks with caffeine were able to absorb and use 26 percent more of the ingested sugar than those who took the same drinks without caffeine. Caffeine-laced drinks help improve endurance even more in hot weather (International Journal of Sport Nutrition and Exercise Metabolism, February 2011).

Caution!
You should take caffeinated sugared drinks only when you exercise and for up to an hour after you finish. Taking sugared drinks, with or without caffeine, when you are not exercising causes higher rises in blood sugars that increase risk for diabetes and cell damage.