Difference between revisions of "The Science Of Hydration"

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== Effects of dehydration ==
 
== Effects of dehydration ==
Everyone knows that dehydration is bad. But how bad? Current research indicates that some level of dehydration (up to 3%) does not impact performance, or impacts performance much less than expected [7]. (Dehydration of 5% does impact performance [11].) This may be due to the fact that carbohydrate (glycogen) is stored with water, in the ratio of about 1g glycogen to 2.5g water [8]. This means that 2000 calories of glycogen depletion that are likely to occur in marathon distance runs would result in about 4lb weight loss with no reduction in hydration (2000Kcal/4=500g glycogen + 1250g water = 1750g). In practice moving from a high carbohydrate to high fat diet can see 6lb weight loss, believed to be glycogen + water depletion [8].
+
Everyone knows that dehydration is bad. But how bad? Current research indicates that some level of dehydration (up to 3%) does not impact performance, or impacts performance much less than expected <ref name="ref7"/>. (Dehydration of 5% does impact performance <ref name="ref11"/>.) This may be due to the fact that carbohydrate (glycogen) is stored with water, in the ratio of about 1g glycogen to 2.5g water <ref name="ref8"/>. This means that 2000 calories of glycogen depletion that are likely to occur in marathon distance runs would result in about 4lb weight loss with no reduction in hydration (2000Kcal/4=500g glycogen + 1250g water = 1750g). In practice moving from a high carbohydrate to high fat diet can see 6lb weight loss, believed to be glycogen + water depletion <ref name="ref8"/>.
 
   
 
   
 
== Salt loss through sweat ==
 
== Salt loss through sweat ==
The amount of salt that is lost through sweating varies a lot. It varies from individual to individual, and for an individual it will vary depending on fitness and heat acclimation [9]. This means that you may have to experiment with your salt intake, both during and after exercise. Anecdotal tip: If your skin is crusty with salt after a run, you are probably someone who sweats out a lot of salt.
+
The amount of salt that is lost through sweating varies a lot. It varies from individual to individual, and for an individual it will vary depending on fitness and heat acclimation <ref name="ref9"/>. This means that you may have to experiment with your salt intake, both during and after exercise. Anecdotal tip: If your skin is crusty with salt after a run, you are probably someone who sweats out a lot of salt.
 
   
 
   
 
== More on Hyponatremia ==
 
== More on Hyponatremia ==
Hyponatremia is where the sodium (salt) levels becomes too dilute. Initial symptoms tend to be a gain in weight and a general swelling and 'puffiness', most noticeable in the hands. More severe symptoms are caused by a swelling of the brain (cerebral edema) including nausea, vomiting, headache and malaise [10].
+
Hyponatremia is where the sodium (salt) levels becomes too dilute. Initial symptoms tend to be a gain in weight and a general swelling and 'puffiness', most noticeable in the hands. More severe symptoms are caused by a swelling of the brain (cerebral edema) including nausea, vomiting, headache and malaise <ref name="ref10"/>.
 
   
 
   
The cause of Hyponatremia is poorly understood, but believed to be related to excessive water intake [1]. (I believe that this is excessive fluid intake in the absence of sufficient electrolytes.) Hyponatremia can be common in endurance athletes. In a 1997 Ironman triathlon, almost 4% of competitors received attention for Hyponatremia [4]. In a study of the 2002 Boston Marathon, 13% of finishers had some level of Hyponatremia, and 0.6% had critical Hyponatremia [2]. The study revealed that the risk factors for Hyponatremia include a slow finish time (&gt;4 hour) and consumption of &gt;6 pints (3 liters) of water during the race; BAA suggests a 'slight build' is also a risk factor[12]. Healthy kidneys can excrete about 2 pints (1 liter) of fluid per hour, but this may be reduced by exertion or illness [3]. So drinking &gt;6 pints in 4 hours could easily exceed the kidneys capacity to cope.
+
The cause of Hyponatremia is poorly understood, but believed to be related to excessive water intake <ref name="ref1"/>. (I believe that this is excessive fluid intake in the absence of sufficient electrolytes.) Hyponatremia can be common in endurance athletes. In a 1997 Ironman triathlon, almost 4% of competitors received attention for Hyponatremia <ref name="ref4"/>. In a study of the 2002 Boston Marathon, 13% of finishers had some level of Hyponatremia, and 0.6% had critical Hyponatremia <ref name="ref2"/>. The study revealed that the risk factors for Hyponatremia include a slow finish time (&gt;4 hour) and consumption of &gt;6 pints (3 liters) of water during the race; BAA suggests a 'slight build' is also a risk factor<ref name="ref12"/>. Healthy kidneys can excrete about 2 pints (1 liter) of fluid per hour, but this may be reduced by exertion or illness <ref name="ref3"/>. So drinking &gt;6 pints in 4 hours could easily exceed the kidneys capacity to cope.
 
   
 
   
The recent rise in Hyponatremia may be due to earlier advice to athletes to "drink as much as possible" [13], combined with a general concern about salt intake.
+
The recent rise in Hyponatremia may be due to earlier advice to athletes to "drink as much as possible" <ref name="ref13"/>, combined with a general concern about salt intake.
 
   
 
   
 
== HypERnatremia - the opposite of HypOnatremia ==
 
== HypERnatremia - the opposite of HypOnatremia ==
Generally, Hypernatremia (too much sodium in the blood) seems to be a result of dehydration rather than excessive salt intake [17]. It should be noted that taking electrolyte capsules bypasses the body's taste. This sense of taste seems to reflect our body's internal sensors; our desire for salty foods reflects our salt requirements.
+
Generally, Hypernatremia (too much sodium in the blood) seems to be a result of dehydration rather than excessive salt intake <ref name="ref17"/>. It should be noted that taking electrolyte capsules bypasses the body's taste. This sense of taste seems to reflect our body's internal sensors; our desire for salty foods reflects our salt requirements.
 
   
 
   
 
== Salt and High Blood Pressure ==
 
== Salt and High Blood Pressure ==
If you have high blood pressure, you may need to be careful with your salt intake. There is evidence that increased salt intake can increase blood pressure [4]. If you have high blood pressure, discuss these issues with your doctor. If your doctor is not an athlete, I would highly recommend changing to one that is. If you don't know what your blood pressure is, get it checked. (As an aside, if you have low blood pressure, which I do, increasing your salt intake can really help.)
+
If you have high blood pressure, you may need to be careful with your salt intake. There is evidence that increased salt intake can increase blood pressure <ref name="ref4"/>. If you have high blood pressure, discuss these issues with your doctor. If your doctor is not an athlete, I would highly recommend changing to one that is. If you don't know what your blood pressure is, get it checked. (As an aside, if you have low blood pressure, which I do, increasing your salt intake can really help.)
 
   
 
   
 
== Caffeine and Alcohol ==
 
== Caffeine and Alcohol ==
The scientific evidence shows that caffeine is generally not a diuretic [5, 14, 15]. Previous studies have shown that if you don't normally take caffeine and then get a large dose, there is some diuretic effect. However normal intakes of caffeine by non-users and use by regular users is not a diuretic [16]. (If you urinate more because you drink a 20oz Latte, it is because of the 20oz of fluid, not the caffeine.)
+
The scientific evidence shows that caffeine is generally not a diuretic <ref name="ref5"/><ref name="ref14"/><ref name="ref15"/>. Previous studies have shown that if you don't normally take caffeine and then get a large dose, there is some diuretic effect. However normal intakes of caffeine by non-users and use by regular users is not a diuretic <ref name="ref16"/>. (If you urinate more because you drink a 20oz Latte, it is because of the 20oz of fluid, not the caffeine.)
Alcohol is another story; drinking anything stronger than 2% will cause dehydration. Because alcohol takes 36 hours to clear the body, it should be avoided for 48 hours before you wish to avoid impaired performance [5].
+
Alcohol is another story; drinking anything stronger than 2% will cause dehydration. Because alcohol takes 36 hours to clear the body, it should be avoided for 48 hours before you wish to avoid impaired performance <ref name="ref5"/>.
 
   
 
   
 
== Muscle Cramps ==
 
== Muscle Cramps ==
The common wisdom that muscle cramps are caused by lack of electrolytes or dehydration does not appear to be supported by science [6].
+
The common wisdom that muscle cramps are caused by lack of electrolytes or dehydration does not appear to be supported by science <ref name="ref6"/>.
 
   
 
   
 
== Blisters and black toe nails ==
 
== Blisters and black toe nails ==
Line 36: Line 36:
 
   
 
   
 
== References ==
 
== References ==
[1]Exercise-Associated Hyponatremia
+
<references>
 +
<ref name="ref1">Exercise-Associated Hyponatremia
 
[http://cjasn.asnjournals.org/cgi/content/abstract/2/1/151 http://cjasn.asnjournals.org/cgi/content/abstract/2/1/151]
 
[http://cjasn.asnjournals.org/cgi/content/abstract/2/1/151 http://cjasn.asnjournals.org/cgi/content/abstract/2/1/151]
 +
</ref>
  
[2]Hyponatremia among Runners in the Boston Marathon
+
<ref name="ref2">Hyponatremia among Runners in the Boston Marathon
 
[http://content.nejm.org/cgi/content/abstract/352/15/1550 http://content.nejm.org/cgi/content/abstract/352/15/1550]
 
[http://content.nejm.org/cgi/content/abstract/352/15/1550 http://content.nejm.org/cgi/content/abstract/352/15/1550]
 +
</ref>
  
[3]Water Intoxication
+
<ref name="ref3">Water Intoxication
 
[http://en.wikipedia.org/wiki/Water_intoxication http://en.wikipedia.org/wiki/Water_intoxication]
 
[http://en.wikipedia.org/wiki/Water_intoxication http://en.wikipedia.org/wiki/Water_intoxication]
 +
</ref>
  
[4]Micronutrient Information Center - Sodium
+
<ref name="ref4">Micronutrient Information Center - Sodium
 
[http://lpi.oregonstate.edu/infocenter/minerals/sodium/ http://lpi.oregonstate.edu/infocenter/minerals/sodium/]
 
[http://lpi.oregonstate.edu/infocenter/minerals/sodium/ http://lpi.oregonstate.edu/infocenter/minerals/sodium/]
 +
</ref>
  
[5]Caffeine dehydration : Caffeine and alcohol - just how dehydrating are they?
+
<ref name="ref5">Caffeine dehydration : Caffeine and alcohol - just how dehydrating are they?
 
[http://www.pponline.co.uk/encyc/caffeine-dehydration.htm http://www.pponline.co.uk/encyc/caffeine-dehydration.htm]
 
[http://www.pponline.co.uk/encyc/caffeine-dehydration.htm http://www.pponline.co.uk/encyc/caffeine-dehydration.htm]
 +
</ref>
  
[6]Muscle Cramps : No link between hydration and cramps
+
<ref name="ref6">Muscle Cramps : No link between hydration and cramps
 
[http://www.pponline.co.uk/encyc/muscle-cramps.htm http://www.pponline.co.uk/encyc/muscle-cramps.htm]
 
[http://www.pponline.co.uk/encyc/muscle-cramps.htm http://www.pponline.co.uk/encyc/muscle-cramps.htm]
 +
</ref>
  
[7]Hydration - fluid intake advice and tips
+
<ref name="ref7">Hydration - fluid intake advice and tips
 
[http://www.pponline.co.uk/encyc/hydration-fluid-intake-advice-and-tips-40789 http://www.pponline.co.uk/encyc/hydration-fluid-intake-advice-and-tips-40789]
 
[http://www.pponline.co.uk/encyc/hydration-fluid-intake-advice-and-tips-40789 http://www.pponline.co.uk/encyc/hydration-fluid-intake-advice-and-tips-40789]
 +
</ref>
  
[8]The Relation Of Glycogen To Water Storage In The Liver
+
<ref name="ref8">The Relation Of Glycogen To Water Storage In The Liver
 
[http://www.jbc.org/cgi/reprint/96/2/367.pdf http://www.jbc.org/cgi/reprint/96/2/367.pdf]
 
[http://www.jbc.org/cgi/reprint/96/2/367.pdf http://www.jbc.org/cgi/reprint/96/2/367.pdf]
 +
</ref>
  
[9]Cracking the Code on Hydration
+
<ref name="ref9">Cracking the Code on Hydration
 
[http://www.active.com/cycling/Articles/Cracking-the-Code-on-Hydration.htm http://www.active.com/cycling/Articles/Cracking-the-Code-on-Hydration.htm]
 
[http://www.active.com/cycling/Articles/Cracking-the-Code-on-Hydration.htm http://www.active.com/cycling/Articles/Cracking-the-Code-on-Hydration.htm]
 +
</ref>
  
[10]Hyponatremia
+
<ref name="ref10">Hyponatremia
 
[http://en.wikipedia.org/wiki/Hyponatremia http://en.wikipedia.org/wiki/Hyponatremia]
 
[http://en.wikipedia.org/wiki/Hyponatremia http://en.wikipedia.org/wiki/Hyponatremia]
 +
</ref>
  
[11]Dehydration reduces cardiac output and increases systemic and cutaneous vascular resistance during exercise
+
<ref name="ref11">Dehydration reduces cardiac output and increases systemic and cutaneous vascular resistance during exercise
 
[http://www.edb.utexas.edu/coyle/pdf%20library/%286329%20Dehydration%20reduces%20cardiac%20output%20&%20increases%20systemic%20&%20cutaneous%20vascular%20resistance%20during%20exercise,%20J%20Appl%20Physiol%2079,%201487-96,%201995.pdf http://www.edb.utexas.edu/coyle/pdf%20library/%2863%29%20Dehydration%20reduces%20cardiac%20output%20&%20increases%20systemic%20&%20cutaneous%20vascular%20resistance%20during%20exercise,%20J%20Appl%20Physiol%2079,%201487-96,%201995.pdf]
 
[http://www.edb.utexas.edu/coyle/pdf%20library/%286329%20Dehydration%20reduces%20cardiac%20output%20&%20increases%20systemic%20&%20cutaneous%20vascular%20resistance%20during%20exercise,%20J%20Appl%20Physiol%2079,%201487-96,%201995.pdf http://www.edb.utexas.edu/coyle/pdf%20library/%2863%29%20Dehydration%20reduces%20cardiac%20output%20&%20increases%20systemic%20&%20cutaneous%20vascular%20resistance%20during%20exercise,%20J%20Appl%20Physiol%2079,%201487-96,%201995.pdf]
 +
</ref>
  
[12]BAA - HYDRATION, DEHYDRATION AND HYPONATREMIA
+
<ref name="ref12">BAA - HYDRATION, DEHYDRATION AND HYPONATREMIA
 
[http://www.bostonmarathon.org/BostonMarathon/WelcomeBooklet.asp#hydration http://www.bostonmarathon.org/BostonMarathon/WelcomeBooklet.asp#hydration]
 
[http://www.bostonmarathon.org/BostonMarathon/WelcomeBooklet.asp#hydration http://www.bostonmarathon.org/BostonMarathon/WelcomeBooklet.asp#hydration]
 +
</ref>
  
[13]USATF Announces Major Changes in Hydration Guidelines for Long Distance Runners
+
<ref name="ref13">USATF Announces Major Changes in Hydration Guidelines for Long Distance Runners
 
[http://www.rrm.com/archive03/042803n2.htm http://www.rrm.com/archive03/042803n2.htm]
 
[http://www.rrm.com/archive03/042803n2.htm http://www.rrm.com/archive03/042803n2.htm]
 +
</ref>
  
[14]Metabolic and exercise endurance effects of coffee and caffeine ingestion
+
<ref name="ref14">Metabolic and exercise endurance effects of coffee and caffeine ingestion
 
[http://jap.physiology.org/cgi/content/full/85/3/883 http://jap.physiology.org/cgi/content/full/85/3/883]
 
[http://jap.physiology.org/cgi/content/full/85/3/883 http://jap.physiology.org/cgi/content/full/85/3/883]
 +
</ref>
  
[15]Effects of caffeine ingestion on body fluid balance and thermoregulation during exercise
+
<ref name="ref15">Effects of caffeine ingestion on body fluid balance and thermoregulation during exercise
 
[http://www.ncbi.nlm.nih.gov/pubmed/2383801 http://www.ncbi.nlm.nih.gov/pubmed/2383801]
 
[http://www.ncbi.nlm.nih.gov/pubmed/2383801 http://www.ncbi.nlm.nih.gov/pubmed/2383801]
 +
</ref>
  
[16]Caffeine ingestion and fluid balance: a review.
+
<ref name="ref16">Caffeine ingestion and fluid balance: a review.
 
[http://pt.wkhealth.com/pt/re/jhnd/abstract.00009862-200312000-00004.htm;jsessionid=KNhWhGQSZnXhY11p2f7qnnmn1Q7z376shvhsK7hTWDLVGQhWpGGJ%21811725889%21181195628%218091%21-1 http://pt.wkhealth.com/pt/re/jhnd/abstract.00009862-200312000-00004.htm;jsessionid=KNhWhGQSZnXhY11p2f7qnnmn1Q7z376shvhsK7hTWDLVGQhWpGGJ!811725889!181195628!8091!-1]
 
[http://pt.wkhealth.com/pt/re/jhnd/abstract.00009862-200312000-00004.htm;jsessionid=KNhWhGQSZnXhY11p2f7qnnmn1Q7z376shvhsK7hTWDLVGQhWpGGJ%21811725889%21181195628%218091%21-1 http://pt.wkhealth.com/pt/re/jhnd/abstract.00009862-200312000-00004.htm;jsessionid=KNhWhGQSZnXhY11p2f7qnnmn1Q7z376shvhsK7hTWDLVGQhWpGGJ!811725889!181195628!8091!-1]
 +
</ref>
  
[17]Sodium Status of Collapsed Marathon Runners
+
<ref name="ref17">Sodium Status of Collapsed Marathon Runners
 
[http://arpa.allenpress.com/arpaonline/?request=get-document&doi=10.1043%2F1543-2165%282005%29129%3C227:SSOCMR%3E2.0.CO%3B2 http://arpa.allenpress.com/arpaonline/?request=get-document&doi=10.1043%2F1543-2165%282005%29129%3C227:SSOCMR%3E2.0.CO%3B2]
 
[http://arpa.allenpress.com/arpaonline/?request=get-document&doi=10.1043%2F1543-2165%282005%29129%3C227:SSOCMR%3E2.0.CO%3B2 http://arpa.allenpress.com/arpaonline/?request=get-document&doi=10.1043%2F1543-2165%282005%29129%3C227:SSOCMR%3E2.0.CO%3B2]
 +
</ref>
 +
 +
</references>

Revision as of 16:41, 25 April 2010

1 Introduction

The advice given to runners on hydration has changed over time and looks set to continue to change. There are competing forces at work - sports drink manufacturers, event organizers (often sponsored by the manufacturers) and scientists (some also sponsored by the manufacturers). One thing is clear about hydration - it is important. Incorrect hydration can lead to impaired performance, and in extreme cases, death.

A condition related to dehydration is Hyponatremia, which is where the sodium (salt) level in the blood becomes too dilute. This is a dangerous condition that has killed a number of runners. More on this later.

This blog entry is a follow on to Practical Hydration which should be read first.

2 Effects of dehydration

Everyone knows that dehydration is bad. But how bad? Current research indicates that some level of dehydration (up to 3%) does not impact performance, or impacts performance much less than expected [1]. (Dehydration of 5% does impact performance [2].) This may be due to the fact that carbohydrate (glycogen) is stored with water, in the ratio of about 1g glycogen to 2.5g water [3]. This means that 2000 calories of glycogen depletion that are likely to occur in marathon distance runs would result in about 4lb weight loss with no reduction in hydration (2000Kcal/4=500g glycogen + 1250g water = 1750g). In practice moving from a high carbohydrate to high fat diet can see 6lb weight loss, believed to be glycogen + water depletion [3].

3 Salt loss through sweat

The amount of salt that is lost through sweating varies a lot. It varies from individual to individual, and for an individual it will vary depending on fitness and heat acclimation [4]. This means that you may have to experiment with your salt intake, both during and after exercise. Anecdotal tip: If your skin is crusty with salt after a run, you are probably someone who sweats out a lot of salt.

4 More on Hyponatremia

Hyponatremia is where the sodium (salt) levels becomes too dilute. Initial symptoms tend to be a gain in weight and a general swelling and 'puffiness', most noticeable in the hands. More severe symptoms are caused by a swelling of the brain (cerebral edema) including nausea, vomiting, headache and malaise [5].

The cause of Hyponatremia is poorly understood, but believed to be related to excessive water intake [6]. (I believe that this is excessive fluid intake in the absence of sufficient electrolytes.) Hyponatremia can be common in endurance athletes. In a 1997 Ironman triathlon, almost 4% of competitors received attention for Hyponatremia [7]. In a study of the 2002 Boston Marathon, 13% of finishers had some level of Hyponatremia, and 0.6% had critical Hyponatremia [8]. The study revealed that the risk factors for Hyponatremia include a slow finish time (>4 hour) and consumption of >6 pints (3 liters) of water during the race; BAA suggests a 'slight build' is also a risk factor[9]. Healthy kidneys can excrete about 2 pints (1 liter) of fluid per hour, but this may be reduced by exertion or illness [10]. So drinking >6 pints in 4 hours could easily exceed the kidneys capacity to cope.

The recent rise in Hyponatremia may be due to earlier advice to athletes to "drink as much as possible" [11], combined with a general concern about salt intake.

5 HypERnatremia - the opposite of HypOnatremia

Generally, Hypernatremia (too much sodium in the blood) seems to be a result of dehydration rather than excessive salt intake [12]. It should be noted that taking electrolyte capsules bypasses the body's taste. This sense of taste seems to reflect our body's internal sensors; our desire for salty foods reflects our salt requirements.

6 Salt and High Blood Pressure

If you have high blood pressure, you may need to be careful with your salt intake. There is evidence that increased salt intake can increase blood pressure [7]. If you have high blood pressure, discuss these issues with your doctor. If your doctor is not an athlete, I would highly recommend changing to one that is. If you don't know what your blood pressure is, get it checked. (As an aside, if you have low blood pressure, which I do, increasing your salt intake can really help.)

7 Caffeine and Alcohol

The scientific evidence shows that caffeine is generally not a diuretic [13][14][15]. Previous studies have shown that if you don't normally take caffeine and then get a large dose, there is some diuretic effect. However normal intakes of caffeine by non-users and use by regular users is not a diuretic [16]. (If you urinate more because you drink a 20oz Latte, it is because of the 20oz of fluid, not the caffeine.) Alcohol is another story; drinking anything stronger than 2% will cause dehydration. Because alcohol takes 36 hours to clear the body, it should be avoided for 48 hours before you wish to avoid impaired performance [13].

8 Muscle Cramps

The common wisdom that muscle cramps are caused by lack of electrolytes or dehydration does not appear to be supported by science [17].

9 Blisters and black toe nails

Dehydration reduces body weight, which can reduce the size of your feet. This in turn changes the fit of your shoes, causing blisters. Hyponatremia can cause swelling, which increases the size of your feet and can cause blisters. Both conditions can also increase the chance of black toe nails.

10 References

  1. Hydration - fluid intake advice and tips http://www.pponline.co.uk/encyc/hydration-fluid-intake-advice-and-tips-40789
  2. Dehydration reduces cardiac output and increases systemic and cutaneous vascular resistance during exercise http://www.edb.utexas.edu/coyle/pdf%20library/%2863%29%20Dehydration%20reduces%20cardiac%20output%20&%20increases%20systemic%20&%20cutaneous%20vascular%20resistance%20during%20exercise,%20J%20Appl%20Physiol%2079,%201487-96,%201995.pdf
  3. 3.0 3.1 The Relation Of Glycogen To Water Storage In The Liver http://www.jbc.org/cgi/reprint/96/2/367.pdf
  4. Cracking the Code on Hydration http://www.active.com/cycling/Articles/Cracking-the-Code-on-Hydration.htm
  5. Hyponatremia http://en.wikipedia.org/wiki/Hyponatremia
  6. Exercise-Associated Hyponatremia http://cjasn.asnjournals.org/cgi/content/abstract/2/1/151
  7. 7.0 7.1 Micronutrient Information Center - Sodium http://lpi.oregonstate.edu/infocenter/minerals/sodium/
  8. Hyponatremia among Runners in the Boston Marathon http://content.nejm.org/cgi/content/abstract/352/15/1550
  9. BAA - HYDRATION, DEHYDRATION AND HYPONATREMIA http://www.bostonmarathon.org/BostonMarathon/WelcomeBooklet.asp#hydration
  10. Water Intoxication http://en.wikipedia.org/wiki/Water_intoxication
  11. USATF Announces Major Changes in Hydration Guidelines for Long Distance Runners http://www.rrm.com/archive03/042803n2.htm
  12. Sodium Status of Collapsed Marathon Runners http://arpa.allenpress.com/arpaonline/?request=get-document&doi=10.1043%2F1543-2165%282005%29129%3C227:SSOCMR%3E2.0.CO%3B2
  13. 13.0 13.1 Caffeine dehydration : Caffeine and alcohol - just how dehydrating are they? http://www.pponline.co.uk/encyc/caffeine-dehydration.htm
  14. Metabolic and exercise endurance effects of coffee and caffeine ingestion http://jap.physiology.org/cgi/content/full/85/3/883
  15. Effects of caffeine ingestion on body fluid balance and thermoregulation during exercise http://www.ncbi.nlm.nih.gov/pubmed/2383801
  16. Caffeine ingestion and fluid balance: a review. http://pt.wkhealth.com/pt/re/jhnd/abstract.00009862-200312000-00004.htm;jsessionid=KNhWhGQSZnXhY11p2f7qnnmn1Q7z376shvhsK7hTWDLVGQhWpGGJ!811725889!181195628!8091!-1
  17. Muscle Cramps : No link between hydration and cramps http://www.pponline.co.uk/encyc/muscle-cramps.htm