I was in a local sport-related establishment recently when I overheard one of the staff members tell a patron that magnesium, and not sodium is the electrolyte to pay close attention to in a sport supplement. I stopped in my tracks thinking – no, that’s not correct. What is she saying? Then I thought, have I missed something in some recent literature? So, I went back to the literature and reviewed the information available.
Before I attempt tackling electrolytes, I want first to note that it comes as no surprise that athletes are confused by nutrition information and for that matter, training, although perhaps less so. There are products professing to be the one thing that will work for the athlete. There are studies released regularly that highlight information about the next magic bullet that will revolutionize one’s training, performance, recovery, life. Let me first say that there are no such magic bullets. There are advances however in research looking at all of these things and studies are being released regularly. Beware of making a decision based on a study of 20-30 subjects (or less). Look for position statements by organizations like the American College of Sport Medicine (ACSM), Dietitians of Canada rather that what someone at the Health Food store told you. These are worth looking at. They boil down and find the nuggets in the multitude of studies that have been published. They rank the studies and proof based on the quality of research and provide solid guidelines that anyone can understand and utilize.
Now, the electrolytes. In endurance sports like marathon, ultramarathon, triathlon, ironman and stage races, it’s important to pay attention to electrolytes. These types of events go beyond drinking water to stay hydrated. In fact, it can become dangerous to drink plain water in copious amounts for hours on end. The longer the event, the hotter the event, the more we need to be paying attention to the electrolytes.
Here’s what the research and the position statements suggests:
Concentration in mmol/L of the major electrolytes present, humans. (Maughan, 1994)
| Plasma (mmol/L | Sweat (mmol/L) | Intracellular (mmol/L) | |
| Sodium | 137-144 | 40-80 | 10 |
| Potassium | 3.5-4.9 | 4-8 | 148 |
| Calcium | 4.4-5.2 | 3-4 | 0-2 |
| Magnesium | 1.5-2.1 | 1-4 | 30-40 |
| Chloride | 100-108 | 30-70 | 2 |
The big losses in sweat are from sodium and chloride. Relative to the content both in the plasma (blood) and intracellularly, potassium, calcium and magnesium are also quite significant but if you look at the intracellular amounts of magnesium and potassium, one could say that there’s plenty in reserve.
Where does the emphasis on magnesium come from? One sport drink maker claims that 70-80% of Americans aren’t getting enough. Hm. The micronutrient magnesium can be found readily in foods such as nuts, whole grains, vegetables and fruit, tea, instant coffee, cocoa powder. Are athletes likely to have these items in their diets? You tell me.
The recommendations from the ACSM in their position stand for Exercise and Fluid Replacement include the following for electrolytes. Direct quotes are included from the journal Medicine & Science in Sport & Exercise, 2007.
Pre-exercise – “consume beverages with small amounts of sodium (20-50 mEq/L) and/or small amounts of salted snacks or sodium containing food at meals will stimulate thirst and retain the consumed fluids”.
During exercise (prolonged activity in hot weather) – “consume a sport drink containing ~20-30mEq/L sodium (chloride as the anion) and 2-5mEq/L potassium and 5-10% carbohydrate.” The amounts will vary depending on many factors including the amount of electrolytes lost in sweat (individual needs), sweat rate and heat, and acclimatization state.
Post-exercise – recovery fluids should amount to 150% of losses and include sodium either through the beverage itself or through a combination of water and salty foods. “Consuming beverages and snacks with sodium will help expedite rapid and complete recovery by stimulating thirst and fluid retention.”
No discussion of magnesium. I maintain that athletes are more likely than the average person – to consume good quality food and more of it. The likelihood of becoming magnesium depleted is slim. The big losses in sweat during exercise continue to be sodium, chloride and potassium. Don’t be fooled.
LiveSplendidly!
Homemade sport drink recipe (modified from Nancy Clark’s Sport Nutrition Guidebook, 3rd Edition.)
4 tablespoons sugar (try maple syrup if you prefer: potassium 46mg/tablespoon and 14g carbs)
¼ tsp salt (sodium 580g)
¼ cup boiling water
¼ cup orange juice (125mg potassium and 6.5g carbohydrate) or 2 tablespoons lemon juice (16g potassium and 1g carbohydrate)
3 ¾ cups of cold water
Instructions:
Dissolve the sugar and salt in the hot water. Add the juice and remaining water. Chill. Drink.