Q+A: Hot-weather salt loss - how should I cope?

Q I’m fortunate enough to spend a lot of my time working, and therefore running, in hot and humid countries. Recently though I’ve noticed that I appear to be losing excessive amounts of salt (evidenced by stains on kit/trainers). I usually take an isotonic drink immediately after exercise. Is this enough, or do I need additional replenishment, and could the loss of salt affect my performance?

A Combining very high temperatures with strenuous exercise obviously means a great deal of sweating, resulting in high salt losses. The good news is that your body is able to adapt to running in very high temperatures – sweat becomes more dilute and less salt is lost – but large electrolyte losses can still occur. This is the reason why many manual workers in warm climes (or in hot working conditions in the UK) are still provided with salt tablets.

For most runners, however, a sports drink should be adequate. I’d suggest 200ml of an isotonic drink just prior to running and 200ml every 15-20 minutes during your run. It would be useful to measure your nude weight before and after runs to see how much liquid you’re actually losing. Each pound in weight you lose while running equates to roughly 450ml of lost liquid, and any loss that occurs needs to be replenished.

To re-hydrate you’ll have to drink one-and-a-half times the fluid you’ve lost. Lose 1lb (454g/450ml) in weight during a run, and you’ll have to drink roughly 700ml of isotonic drink to replace it. Try to eat plenty of bananas, fruit juices, vegetables and fresh foods to ensure adequate mineral intake. Also do not completely eliminate salty foods from your diet. These will help to ensure you have adequate electrolytes to balance fluid losses each day.

Joe Beer, sports scientist and level two triathlon coach