It is probably the greatest fear of every endurance runner: Don’t get dehydrated! Many ambitious hobby runners therefore drink liters of water in advance during longer sessions. Can’t hurt. Or is it?
“You shouldn’t drink at every opportunity during a long running session – for example a marathon,” says Juliane Heydenreich, junior professor for nutrition and sport at the Johannes Gutenberg University in Mainz. Because if you drink too much, you not only carry unnecessary ballast with you, but also endanger your own performance.
This has to do with one substance in particular: sodium. It plays an important role in regulating fluid balance in the body and blood pressure. If you run for a long time, you will sweat a lot over time. It contains a lot of sodium (in the form of sodium chloride, i.e. salt).
The problem: Most mineral waters contain hardly any sodium. And not without reason. In the normal diet, sodium and salt consumption should be kept low if possible, otherwise there is a risk of high blood pressure in the long term. However, if the sodium level in the blood drops too much while running, there is a risk of a deficiency that can lead to dizziness and weakness up to and including collapse – also known as “water intoxication”. “That’s why it’s important not only to compensate for the loss of fluids, but above all for the loss of sodium,” says Heydenreich.
Ambitious endurance runners should make sure they drink mineral water with a higher sodium content or use isotonic drinks during their sport. The ratio of electrolytes to liquid in these drinks is roughly the same as in human blood, which is why they are particularly well absorbed.
They should also determine their own drinking needs precisely: “It is best to weigh yourself immediately before and after running units under different conditions in order to determine the weight loss caused by sweat.” Don’t forget: also calculate the water consumed. “A loss of two to three percent of body weight is tolerable, anything more than that should be compensated for with suitable drinks,” recommends expert Heydenreich.
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