Low blood sugar in  endurance athletes
By Artour Rakhimov

	This paper describes symptoms, effects, and causes of low blood sugar (hypoglycaemia) in active endurance athletes. Recommendations to improve the situation are provided. The paper can be useful for those who have problems with low blood sugar and for those who are interested in own physiology and influence of exercise. 
Blood sugar values
	Let us imagine that there are no other health concerns and we are interested only in the influence of blood glucose level on the well-being of the person.  
A healthy individual has fasting blood glucose level (e.g., in the morning) 4-6 mMol (mmol/l). These values correspond to clear mind, feelings of energy and optimisation of many physiological parameters (lowest values of pulse, minimum blood pressure and lowest volume of lungs' ventilation). The person can be happy and even intriguingly smiling (as La Giakonda, or Mona Lisa, who, probably, knew how to be in this state during long hours of Leonardo’s drawing).
When levels are 2-3 mMol (hypoglycaemia), feelings of hunger, irritability, forgetfulness, and muscle weakness (usually calves) develop. Further decrease in blood sugar is additionally accompanied by decline in short term-memory (that leads to inability to concentrate since most recent events and facts are forgotten), feeling drowsy, cold skin (especially extremities), pale face, trembling, sweating, heart palpitations, and craving for sweets. Some of these symptoms are caused by adrenalin release in order to raise blood sugar back to normal since glucose is the brain's fuel. This bodily response is normal in order to prevent unconsciousness, seizure-like activity and/or other neurological manifestations in those rare cases when the level is below 1 mMol. The symptoms can vary from person to person.
If blood sugar is too high (that is very rare among serious athletes), then starting from 9-15 mMol kidneys begin to eliminate excessive sugar from blood into urine in order to prevent cell poisoning. That leads to frequent urination, dehydration, thirst, blurry vision, fruity breath, nausea, vomiting, laboured breathing, weak and fast pulse. Repetitive diabetic attacks can cause damage to kidneys, eyes, nerves and blood vessels.
Factors affecting blood glucose
There are many factors that define daily blood glucose fluctuations. Most significant are the precision of the response of pancreas to secrete insulin (so that cells can, obeying the order, take glucose from blood and use it) after meals, meals pattern, exercise and stress. All job of blood sugar regulation is done through the hormonal influence.
Main hormones affecting blood sugar
	There are two glands and five main hormones which directly influence blood glucose concentration.
1.	The islets of Langerhans in pancreas can secrete insulin and glucagon in response to blood sugar variations according to the given diagram (Fig.1).

Islets of Langerhans

Insulin

Glucagon

Blood glucose concentration

			       Stimulates			   Depresses

                Lowers			Raises

					Fig.1.

 As one can see, insulin secretion is based on positive feedback regulation mechanism. When blood sugar level rises, the islets produce more insulin. When it falls, less. A negative feedback mechanism can be found for the rate of the glucagon secretion. Since blood glucose concentration is so important for the whole organism, we have two independent mechanisms to control it. The insulin's job is to transport fuel to cells, so that they can function normally and to store sugar excess in liver in the form of glycogen. Glucagon stimulates liver to release glucose into blood and increases formation of glucose from lactic acid and certain amino acids also in the liver. Although both these hormones are constantly present in the blood and working, insulin's role becomes especially important after meals in order to store energy, whereas glycagon's role is to release energy, for example, during exercise.
2.	 Adrenal glands can secrete three other glucose-affecting hormones: cortisol, adrenalin and nor-adrenalin.
Cortisol stimulates the conversion of fats and proteins into glucose and its release is controlled by corticotrophin (also called ACTH) from the pituitary gland (also called master gland). Corticotrophin is released in response to stress. Apart from anti-inflammatory properties, cortisol increases alertness of body organs to stress (it supplies ATP in conditions of fright, temperature extremes, high altitude, surgery, exercise, etc.). Thus, as soon as there is something unusual (either from the organism or perceived by individual senses as life-threatening), the blood level of cortisol raises. This hormone has strong circadian cycle. It is low during the night, lowest in the early morning hours, and high during the daytime.					
Adrenalin and nor-adrenalin are also released as a response to stress either of perceptual nature or low glucose supply for the brain. The role of these hormones is more global. They do not only raise blood sugar (by stimulating liver to convert glycogen into glucose), but also influence almost every organ according to sympathetic activation.
Many other hormones are capable, in lesser degree, to influence blood glucose concentration usually by changing the levels of the above-mentioned hormonal substances.
After-meal fluctuations
A healthy person after consumption of 100 g diluted glucose (50 and 75 g are also used in different countries) and consequent rest for several hours during prolonged glucose tolerance test (GTT) has a following blood glucose curve (curve 1 on Fig.2). Nearly the same reaction would be observed after eating, for example, 200 g white bread or 400 g mashed potatoes.		 

Curve 1

   6

Curve 2

   4

Curve 3

								

  2   

					Fig. 2.
The blood sugar level slightly drops at the beginning (stomach started to work) and then raises by 1-2 mMol in 1-2 hours. During this time islets of Langerhans in pancreas secrete more insulin than during previous fasting due to both natural physiological programming and learning which took place during digestion of previous meals (digestive system has its own brain and orchestrates all its organs together with the types and amounts of digestive juices secreted by the same pancreas and other organs, like mouth and stomach). As a result, the level after reaching its maximum (that is still below 7) gradually declines to the initial fasting level. That indicates precise pancreatic regulation, continuous mental alertness, feeling of well-being and even the possible intriguing smile.
When the response of pancreas is not that accurate or when the problem develops, we have either a delay in the appearance of the adequate insulin levels or less effective insulin. In both cases, the sugar level can go up to 7-9 (or more in case of diabetes). Such high values cause alarming situation for the islets and too large amounts of insulin can be found in the blood. Now glucose is urgently driven into cells and liver and its blood glucose level sharply goes down reaching its minimum which can be 0.5 - 2 mMol lower than the initial fasting level (curve 2 in Fig 2). The appearance of this hole with the USUAL depth of 0.5 – 2 mMol is called reactive hypoglycaemia since the low blood sugar level here is the reaction to the meal.  Organic hypoglycaemia is associated with low fasting (initial) sugar level. It is also possible to have both of them (low initial level and even lower post-meal minimum values). Such response is presented by the curve 3 in Fig.2. This graph is even less smooth near the bottom due to the influence of stress hormones which are usually released when the level is about 2.5 or less.
Let us look at the influence of the amount of eaten food. Curve 2 (Fig.3) is taken as a base from the previous graph. Larger meals with the same type of food cause even higher maximum values and lower minimum values (curve 4 in Fig.3), whereas for smaller meals the fluctuations are more smooth (curve 5 in Fig.3). These graphs are approximately received by either expansion or shrinking of the initial curve in horizontal and vertical directions. 

					Curve 4

			   Curve2
   6
		    Curve 5

   4

  2   

					Fig. 3.

Better reaction is observed for foods which carbohydrates and other nutrients are absorbed into blood slower. In order to reflect this phenomenon of different absorption rate, scientists introduced GI (glycaemic index). Those foods mentioned above have nearly maximum GI 100%. There are many foods with lower GI (e.g., fruits, most vegetables, nuts, seeds, lentils, sprouts, fish, meat, dairy products, fats and their combinations). The law of proportions can be applied in order to define the GI of combined foods whereas some books and internet sites can provide GI tables.
Fig.4 reflects the influence of meals with different GI. A meal with same calorie intake but with GI about 50% can approximately produce the sugar level increase (curve 6 in Fig.4) which is approximately twice less then the increase for 100% GI meal (curve 2) and which is about two times later in time. The depth of the hole is likely to be about twice smaller as well, as it is shown on the graph. Here, the effect of the GI is obtained by vertical shrinking and horizontal expansion.

	      Curve2			
   6						  Curve 6

   4

  2   

					Fig. 4.

The important principle for reactive hypoglycaemia to remember is that the higher the maximum the lower the minimum.
The glucose fluctuation is different if the same meal is eaten in different hours of the day. The first meal after fasting (hence the name “breakfast”) gives worst curves. Consequent meals are better tolerated and corresponding blood sugar graphs are smoother.
Continuous exercise
	If the person, without any preparation, starts some steady low-intensity physical activity (e.g., slow running or cycling), his blood sugar falls within first several minutes (curve 1, Fig.5). At that moment more cortisol and glucagon (and less insulin) are secreted into the bloodstream stimulating the liver to release more glucose into blood. That leads to blood glucose stabilisation. Note, that the glucose concentration can be quite low (1.5-2 mMol), but the main stress hormones (adrenalin and nor-adrenalin) are not released because the rate of the fuel supply for the brain remains nearly normal due to increased cardiac output. 
	In the intensity of this steady activity is higher, then some amount of stress hormones can be released near the minimum point (curve 2 in Fig.5). Later, after the head is happy, their levels return back to normal. As a result, in some 10-20 minutes, after initial discomfort, the person feels better and can even enjoy his activity.

   4

  2   					Curve 1

					Curve2
					Curve3

					Fig. 5.

	Only if the activity is too intensive (e.g., near maximum possible) and blood sugar level is about 1 mMol or less (curve 3 in Fig.5), then the urgent messages from the brain will require presence of large amounts of adrenalin and nor-adrenalin blood in order to keep blood glucose from being too low for the brain to adequately function.
Other factors
Different other factors (stress and inner processes) create particular levels of different hormones. Stressful events without physical activity lead to pancreatic response deterioration. Although adrenalin and non-adrenalin temporarily raise blood sugar, they do not usually present in the body for a long time (unless the person has sympathetic stress) and after their levels drop the total hormonal profile is worse than the initial one if there is no physical outlet for the emergency situation. Such response is another normal physiological reaction. Indeed, although textbooks often describe "fight or flight" response in animal kingdom and for humans, the reaction is not always so. Many animals adopted another response which can be called "hide-response" or passive reaction. It is, indeed, of survival value for many animals to be de-mobilised in holes, dens and nests for hours if there are dangerous predators around. 
Although humans do not need to follow "fight or flight" choice (they can, for example, look surprised, shrug shoulders or walk away from the unpleasant situation), it would be wise to have daily physical workouts in order to restore active hormonal balance since stress is a part of human perception (in the absence of real outside stressors, the head can invent them). Thus, improvements in glucose tolerance are observed after exercise (with gradual reduction of the effect in 1-2 days). More detailed hormonal profile for active and passive responses can be found in textbooks on human physiology.
Practical symptoms
In practice, a person feeling hungry, when the level start to drop below about 3-3.5, has a snack or the next meal. An athlete can have a workout. It also prevents his brain's fuel supply from falling too low. As a result, in both cases the problem may not be noticed. But there is another effect caused by hypoglycaemia and which may not go unnoticed. It can be called morning hypo crisis. Let us look at its gradual development. 
A healthy person soundly sleeps till 6-8 a.m. without interruptions and awakes refreshed and full of energy with no hunger (in fact, he should feel even less hungry than when going to bed last night). When glucose tolerance worsens, the person starts to awake about 1-2 hours earlier than usually with possible hunger. He opens eyes, looks at the clock, close eyes, look again a moment later only to realize that about 1 hours has passed. With further deterioration, he awakes at 4-5 a.m. and can not sleep for 10-20 minutes (at that moment his blood sugar level is likely to be less than 3). 
When the level drops below 2-2.5, he awakes with cold sweats, racing heart (pulse can be 10-20 beats more than normal) and other symptoms of adrenalin rush. Unless a small snack is consumed (100-200 kCal), he can not sleep for 1-2 hours. Such sleep interruptions affect organism's cycles together with mental and physical recovery.
Use of exercise as a stress
Now how different types of training and sport experience come into the play. If a person does some active physical work, then more glucosteroids (especially, cortisol) from adrenal glands are released in response to this physical activity. The effect of this hormone lasts for several hours. That explains why people feel refreshed after light exercise.
If the physical activity is anticipated than the chain of hormonal events (similar to "fight or flight" response) raising blood sugar in advance can take place. But unexpected physical exercise can produce hypoglycaemia when there is no time for stress hormones and cortisol to do their job.
As a result, hypo athletes usually do not have problems with blood sugar during important competitions. Even if they skip their breakfast (or it is small), the situation of competitions with numerous triggers activates the sympathetic nervous system, with corresponding stress hormones and sufficient blood sugar. Similar chain of events usually can take place before the training workout provided that the athlete is motivated to perform, but after such workouts (without meals), the problem can be very serious.
Why is there different response to low blood sugar in two following situations?  During the morning hypo crisis or after large high GI breakfasts (or during the GTT) the main hormones raising blood sugar are stress hormones, whereas during monotonous exercise the same problem of low blood sugar is mainly solved by glucagon.
Stress hormones are released either in response to perceptual stimuli (stress from outside) or to inadequate supply of energy to the brain, as during the morning hypo crisis or GTT. Glucagon also contributes to the process.
During continuous aerobic exercise, although the concentration of blood sugar can be low (e.g., 1.5-2 mMol), the brain fuel supply is normal due to increased cardiac output. So, no stress hormones are necessary. Thus, in this case only or mainly glucagon corrects the problem and raises or keeps general blood sugar level.
With years of training the pancreas secrete less and less glucagon in response to exercise due to adaptation. But it is possible to have more glucagon and stress hormones in blood by doing more intensive, especially interval, exercise. For example, during interval training the pulse during periods of rest drops significantly. In this case, the fuel supply for the brain becomes insufficient and the pituitary gland sounds alarm. Stress-hormones are released; profuse sweating and slight disorientation can be noticed, as a result of a short (1-2 minutes) hypo crisis which is normal for healthy athletes as well. If this pattern is repeated many times, the final level of adrenalin and nor-adrenalin responsible for feeling energised (not just fresh as after light work) can be very high. That causes more active state of the sympathetic nervous system after interval training. Also, the whole sporadic or periodic structure of such exercise contributes to sympathetic activation.
Hence, if an experienced athlete has a problem with low blood sugar, he is going to favour intensive interval workouts because they help him to keep normal blood sugar values for about a day. Such situation improves his well-being, including sleep pattern. Low intensity workouts and monotonous training (especially with low pulse, without pulse variation, and parasympathetic over-activation) does not improve his problem. In addition, very long workouts deplete body carbohydrates. Larger calorie intake further exhausts pancreas and can resonate blood glucose swings. When the weather is cold, the athlete becomes very prone to colds, since post-exercise hypoglycaemia does not allow muscles to shiver and can lead to hypothermia. First symptoms of illness can appear in the matter of hours making him sick for at least a day.
Thus, the training of such athlete may be dictated by poor blood sugar regulation instead of seasonal needs although such type of training can be normal for players, sprinters and other athletes.
Why the problem develops
People developing blood sugar problems generally have low chromium and zinc levels. Numerous studies indicate that chromium deficiency makes insulin less efficient, whereas chromium supplementation helps to even out glucose levels by decreasing insulin requirements. Chromium is now considered not essential for human health and is the most likely next candidate for the "promotion" (it is surprising that nobody on the Earth knows the work of the single cell and the roles of hundreds of body chemicals are not understood, but there are people who assert that some nutrients are essential, while others are not). Zinc is needed for release of insulin by the pancreas. Marginal deficiencies in magnesium, vitamins C and B-complex can also contribute to the problem.
Quick silver
There is now mounting scientific evidence that one of the problems created or worsened by silver amalgams (which are banned for all people in some countries or can not be used for the pregnant and with kidney problems in others) is poor glucose tolerance. It can appear even for people with relatively healthy eating patterns. Such amalgams are 50% mercury gradually leaching in its elemental form out of the fillings especially when their owners chew, brush teeth, or sit in front of computers. Since mercury is the most toxic element on the Earth, amounts measured in nanograms can cause, after years of accumulation in organs (especially, the pituitary gland), different health problems, including games with blood sugar.  
Other causes of the problem
Large changes in the average Western diet and lifestyle have taken place during last century.
1.	Larger amounts of food in terms of calories are consumed (larger meals more work for pancreas), while the lifestyle became more passive (for those who are not much involved in physical activity) or more sporadic (e.g., for athletes). People often eat when upset, angry, anxious, sick; overuse spices; have irregular meal times; drink with meals in order to swallow; do not properly chew food; eat too fast. All these factors overburden gastric organs for extra-digestive juice secretion causing stomach over-acidity (that, in turn, exerts more demands on liver and pancreas to neutralise too acidic chime).
2. The amount of fibre intake decreased about 3-5 times while less raw food is eaten  (less fibre- higher GI, cooked food – generally higher GI).
3. Wholemeal bread was substituted with white one (40-50 times less chromium, 3-4 times less zinc, 5-6 times less magnesium) and brown rice with polished one (3-4 times less chromium, twice - zinc, 5-6 times magnesium).
4. Intake of saturated fats increased more than 2 times, hydrogenated fat isomers 10 times as substitutes for other nutritious foods (hence, less important nutrients are provided).
5. Sugar intake increased many tens-hundreds times (no minerals, higher GI, extra-work for pancreas and leaching of chromium).
6. Widespread use of soil fertilisers decreased the amount of minerals in the soil and produce (zinc up to 2 times according to many sources).
Now, try to imagine what would happen with a car after years or running which is provided with several times less engine oil (or transmission oil) then it was designed, tested and required by engineers.
Before contests
30-40 years ago, as well as before that, an empty stomach was considered a necessary condition for optimum performance, be it a mental test or a sport event (from sprint to marathon). Moreover, some professional marathoners and coaches believed that no solid food could be taken during last 8 hours before important races. That means not only empty stomach, but almost the whole small intestine as well. The reasoning behind those ideas was simple. Since digestion takes about third of total calorie intake (three muscle layers in stomach, two in the small intestine, and small sporadic movements in the colon), it would be sensible to give it a rest. That is possible only when the stomach and the intestine are empty, since peristalsis starts there as soon as there is something to digest or move. Energy can be taken from drinking juices or specially prepared drinks before the event (so that they leave the digestive system before the beginning of the contest); liver, muscles and fat provide fuel during the contest. Normal glucose level should be supported by stress and exercise hormones. Those experimental results generally agreed with such advice (at least empty stomach even for mental tests).
Modern results are different and that can be expected since changes in the diet produced changes in the glucose levels. If a large part of experimental subjects have low fasting or initial glucose level or it falls too significantly during the test, it would be necessary for them to have outer nutritional support in order to perform better.
Whatever the way that is chosen by the athlete, the root of the problem is to have normal glucose response and normal fasting levels. Otherwise, temporary solutions (like sugary or glucose drinks before and during contests) can worsen the main problem.
What can be done?
1.	Remove all mercury from the head. Check your stool for parasites (another "contributors").
2.	Follow the chosen eating pattern (in terms of chewing, glycaemic index and amounts of food, intervals between meals, activities in between, etc.). That especially relates to the breakfast when the ability to regulate blood sugar is lowest. 
3.	It may be beneficial to restrict the consumption of following foods for a while: bananas, barley, cabbage, garlic, lettuce, oats, olives, onions, papaya, turnip, and sweet potatoes. As reported, they encourage pancreas to produce more insulin and are good for diabetics (so called functional foods).
4.	Take daily supplements for about 1-2 months to observe changes. Essential (daily): Cr - 200-400 mcg, Zn  15-30 mg (both only in organic or amino-acid chelated form, not oxides or inorganic salts), high strength vitamins C and B-complex. Provisional: Ca, Mg, Mn, and K.
5.	Essential fatty acids: Omega 6 oils (in many nuts, seeds, or starflower and evening primrose oils) help insulin to work, whereas Omega 3 oils (found mainly in fish) can help to reduce possible pancreatic inflammation due to increased production of series 1 and 3 prostaglandins. Such long-term strategy can be effective even for sport injuries (problems with ligaments, tendons, bones, etc), especially with simultaneous restriction of animal fats (no butter, no meat, skinless poultry, low fat yoghurt, low fat milk, low fat cheeses, etc.) 
6.	Exercise: Days of total rest usually worsen hypoglycaemic attacks. Thus, do some easy but exciting activity (e.g., games) for about 40-60 minutes. Make aerobic workouts more variable in terms of pulse. Often even slim athletes loose 1-2 kg weight during their basic period and recover back during competitions. That is normal and should not be feared.
7.	GTT: Arrange glucose tolerance test done by medical personnel or do it yourself using a blood glucose monitor.
8.	Check your pulse 2-3 hours after meals with high GI and early in the morning if you suspect a hypo attack. In case of food allergies the pulse increases by at least 5-10 beats per minute after 30-60 minutes, whereas hypoglycaemia can be observed about 2-3 h after the meal (the resting sitting pulse increase can be 10-20 beats or higher). Early in the morning, in case of hypo attack, the lying pulse can be only 10-15 beats higher, while the standing pulse can increase by as much as 20-30 beats. Standing position requires about 60% more energy. As a result, it is more sensitive to low blood sugar.
9.	In case of early morning activities (e.g., 2-5 a.m.), do not rush immediately after awakening since memory problems, poor coordination and other symptoms of low blood sugar are normal at that time even for healthy people. Drink a glass of juice and wait for 5-10 minutes in order for fructose to be absorbed.
10.	Water fasting, for about 5-7 days or juice fasting for 10-12 days, can solve the problem completely. But such treatment must not be taken without supervision of a health professional who have experience and training in this area. For example, inappropriate breaking of such long fasts can seriously damage digestive organs or very low level of some blood electrolites can create big problems. Also note that it would take weeks to restore previous fitness and normal weight.

November 1998

2010 Update. It is beyond any doubt, that when one of the simplest and easiest ways to normalize blood sugar control is to normalize one’s breathing pattern or to breathe slower and lighter (reduced minute ventilation and breathing frequency). The explanation and details of breathing retraining can be found on the website www.NormalBreathing.com