Electrolyte drinks- what to look for and avoid

An electrolyte replacement drink, powder, effervescent tablet or gel aims to replace the missing electrolytes, nutrients, or minerals that are eliminated through perspiration and muscle metabolism during intense exercise.
This is essential to prevent exercise associated hyponatremia (low  blood sodium) or other deficiencies.
There are many brands available on the market so no doubt there will be some confusion there!
So what to look for:

• Sugar: No carbohydrate intake is required in exercising less than 45 minutes, however above this, your body starts to require glucose as a source of energy.  Under 2 hours of exercise, you would need up to 30 g of carbohydrate per hour and above 2 hours, up to 60 g per hour. In iron man competitions, up to 90 g per hour is required after the 2 initial hours. Glucose is the most bioavailable form. The recommended range for glucose intake is 4-8%, or maximum 8 g per 100 mL water. More glucose or sugar than 8 g/L in a drink will generate stomach discomfort. Soft drinks such cola drinks contain about 10 g sugar per 100 mL, which is above 8g/L.
• Beware of synthetic forms such as sucralose and aspartame which have detrimental effects on the gut microbiome (healthy bacteria).
• Water: How much water should you have? As a general rule it is best to have small amounts of fluid at a time, around 150-200 mL every 5-20 minutes, depending how heavily you sweat.
• Magnesium: It is an important electrolyte in order to prevent cramping and reduce plasma lactate. The best form is magnesium citrate. If your drink contains magnesium oxide, it is certainly cheaper but it will be poorly absorbed and can cause diarrhoea, which you want to avoid at all costs during a race!
• Citrates: Another benefit in having citrates as magnesium or calcium is the fact that they bind to acid forming compounds hence reduce the acidity formed by intense exercise. They also prevent kidney stones formation.
• Sodium: Exercise associated hyponatremia (EAH) can occur when sweating heavily, or after two hours of intense training when your only source of fluid is plain water. 10-25mmol/L or  230-570 mg/L sodium would be sufficient in most cases.
  

Symptoms of hyponatremia include: 
Mild

•  Bloating
• Puffiness
• Nausea
• Vomiting
• Headache
• Lethargy
• Loss of coordination

Severe 

• Worsening cerebral oedema
• Altered mental status: confusion, disorientation, agitation
• Seizures
• Pulmonary oedema
• Coma and death

• Preservatives: Avoid preservative-containing gels, tablets or powders since they can affect your digestive system. Polyethylene glycol, a preservative found in effervescent tablets can potentially release formaldehyde, a toxic chemical.

Resources

Bergeron M. 2007 'Exertional heat cramps: Recovery and return to play.' J Sport Rehabil ; 16:190-196.

Sawka M, Burke L, Eichner R, Maughan R, Montain S, Stachenfeld N. 2007 'Exercise and Fluid Replacement.' Position Stand. Med Sci Sports Exerc ; 39:377-390.

Schwellnus MP. 2009'Cause of exercise associated muscle cramps (EAMC) — altered neuromuscular control, dehydration or electrolyte depletion?' B J Sports Med ; 43:401-408.

Walker, AF, Marakis, G, Christie, S & Byng, M 2003, ‘Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study’, Magnesium Research, vol. 16, no. 3, pp. 183-91.