Isotonic drinks are drinks whose osmotic concentration (osmolarity) is similar to that of human blood. By presenting a similar osmolarity, these drinks favor a correct rehydration and for this reason they are widely used in sports circles. They are usually composed of water, mineral salts and simple carbohydratesmainly glucose, so they not only rehydrate but also replenish electrolytes lost during physical activity and provide highly available energy to help the athlete recover.
The osmolarity of human blood plasma is approximately 290 mOsm/L, the same as that obtained in a solution of 9 grams of NaCl (common salt) in one liter of water. Beverages with a higher osmotic concentration would be hypertonic beverages and beverages with a lower osmotic concentration would be hypotonic beverages.
When the osmolarity on both sides of a cell membrane is the same, there will be the same osmotic pressure outside and inside the cell. In this case, the cell is said to be in a isotonic medium. When a cell is located in a medium with a higher osmolarity than its interior, it is said to be in a hypertonic medium. In this case there is a higher osmotic pressure on the outside and the water will flow towards the outside of the cell until the osmolarity equalizes. The cell will be dehydrated. In hypotonic media the opposite would happen, the osmotic pressure inside the cell is greater and the water would flow inward. If the difference in osmolarity is high enough, the cell could burst.
When there is a situation of loss of fluids and mineral salts, for example after physical exercise, isotonic drinks favor the correct recovery of water and electrolyte levels Hypertonic drinks would be counterproductive as they could worsen dehydration by causing the exit of water to the intestine due to its greater osmotic pressure (similar to what happens when you drink sea water). Hypotonic drinks could serve to replace lost water but could be inefficient to recover mineral saltsthey could even trigger a greater loss of electrolytes.
Most commercial isotonic drinks are known as sport drinks since they are specifically designed to replenish the water and mineral salts that are lost with sweat when intense physical activity is carried out. But isotonic sports drinks are actually slightly hypotonic and, in addition to water and mineral salts, they also contain glucose or other simple sugars that provide quickly available energy. The sugar content is responsible for sports drinks also helping to improve performance if consumed during exercise by avoiding sudden drops in blood sugar.
In addition to sports, isotonic drinks are used in any state with a risk of dehydration. For example, isotonic drinks are often prescribed patients suffering from diarrhea or vomiting. With both diarrhea and vomiting, large amounts of water are lost and there is a risk of dehydration that isotonic drinks help prevent.
homemade preparation
There are numerous recipes to prepare isotonic drinks with properties and characteristics similar to those of commercial isotonic drinks. The most common are known as alkaline lemonade and oral rehydration salts.
alkaline lemonade
- 1 liter of water
- juice of 2 – 3 lemons
- 1 pinch of salt (half a teaspoon of dessert)
- 1 pinch of baking soda (half a teaspoon of dessert)
- 2 tablespoons of sugar
Oral rehydration salts
Oral rehydration salts is an isotonic formula that is usually available in pharmacies and has been promoted by the WHO as a rehydration formula. Its composition is:
- 1 liter of water
- 2.9 g of potassium chloride
- 3.5 g sodium chloride
- 2.5g baking soda
- 20g of glucose
Not to be confused with energy drinks
Isotonic or sports drinks should not be confused with energy drinks. Energy drinks contain stimulating substances, such as caffeine or ginseng, and are not indicated for rehydration. In fact, energy drinks are often hypertonic and could worsen a dehydrated state.