Potassium and hydration
There are two potential mechanisms that reduce the effectiveness of a sports drink for hydration when the ratio of potassium to sodium is not correct.
1) Drinks with too much potassium will cause the kidneys to start removing that potassium from the bloodstream. The way they do this is by extracting the potassium and then excreting it in urine. When the kidneys do this, there is a removal of potassium, a small loss of water through the excreted urine, and because the kidneys are not perfect, they will also include some sodium in that urine. So, too much potassium causes the loss of fluid and sodium, effectively achieving the opposite of what was intended when the athlete hydrated.
2) The potassium that is not removed by the kidneys will be absorbed into tissues. This will create an osmotic pressure for water and sodium to be drawn out of the blood plasma and into tissues. Again, this is not what athletes want, as maintaining blood volume is important for sustaining their performance level.
These two mechanisms mean that potassium in a sports drink is more likely to reduce its effectiveness for hydration, which is not what we want.
What about potassium in sweat?
Yes, we do lose some potassium in sweat, but it's close to negligible. The loss of potassium is approximately 250 mg/L compared to sodium losses which can range from 400 mg/L to 2600 mg/L. As these losses are minimal, the body has enough potassium stores, making it unnecessary to replace it during exercise.
What about potassium and cramping?
Unfortunately, cramping is a problem that doesn't have a clear cause and is often just a function of performing at an intensity that is greater than the athlete is prepared for. Many of the "solutions" for cramping rely on different mechanisms rather than being related to potassium intake.
For example, bananas contain potassium, but it is probably the carbohydrates that provide fuel and help meet the demands of exercise. Similarly, tart juices, mustard, or pickle juice work through different mechanisms that affect brain-muscle communication rather than being effective because they contain potassium.
What is the key takeaway here?
The simple answer is that you don't need potassium in your sports nutrition. Keep it simple and stick with carbohydrates and sodium.
