The Salt Story
by: Fiona Pelly
I thought it would be worthwhile discussing sodium requirements for athletes. Most Australians do consume too much salt or sodium , but does this apply to those who exercise?
Sodium is needed to balance the amount of water within the cells of our body. The level of sodium in our body is carefully maintained by the kidneys. If we eat salty foods more sodium is excreted, while a diet low in salt results in reabsorption of sodium back into the blood. Sodium is also lost via sweat, however athletes and those who live in hot climates are more efficient at diluting their sweat. Athletes are also better at reducing loss of sodium through the kidneys. As most athletes eat more food than the average non-exerciser, they also tend to consume higher levels of sodium. For this reason most athletes do not require additional salt in their diet.
Loss of sodium through sweat can become a problem during ultra-endurance events (or continuous exercise that lasts over 4 hours). Risk groups are:
- Those who sweat profusely and only partially replace this loss with water or a low sodium drink (otherwise known as hyponatraemic dehydration)
- Those who have a low sweat rate who consume excess amounts of water in effect diluting their sweat (water intoxication).
Both situations can easily be rectified by substituting water with sports drinks. To make sure adequate sodium and fluid is obtain, drink a sports drink with a concentration of 20-30 mmol sodium. (46mg-69mg per 100mls) This should be stated on the label. Note that although most sports drinks contain some sodium, not all contain this higher concentration.
The first sports drinks introduced in the 1970's contained high levels of sodium to mimic the composition of sweat. It was originally thought that significant levels of sodium were lost in sweat and must be replaced, which we now know is not true (except in the extreme cases mentioned above.) Why then are sodium and other minerals added to sports drinks ?
The reasons are outlined below:
- Sodium increases the speed at which fluid and glucose is absorbed into the body. This means that we are less suseptible to dehydration and thus can exercise for longer or at a higher intensity.
- Sodium improves palatibility as it offsets the sweetness of the added sugars. There is also some evidence that after exercise and when dehydrated most people have a preference for a slightly salty tasting beverage
- Sodium and other electrolytes do need replacing in ultra endurance events over 4 hours.
The most common problem arises in those who sweat profusely, as they are at risk of both dehydration and sodium depletion. Many athletes don't drink enough on a day to day basis and often go into events already partially dehydrated. Fluid is absorbed faster if small amounts are drunk regularly. If already dehydrated, fluid will be absorbed slowly and may sit in your stomach or cause a stitch during running. This often results in the athlete drinking less due to discomfort, which of course exacerbates the problem! Dehydration can also cause gastric upset, so runner's diarrhoea can be caused by lack of fluid as much as by the food you eat beforehand. Loss of as little as 2% of body weight can decrease exercise performance even at low intensities . Dehydration can also affect mental functioning and co-ordination. Most seriously, a loss of 5-6% body weight due to dehydration becomes dangerous and can result in heat stroke and death.
Start by drinking regularily throughout the day. Don't save up until training. Check the colour of your urine. This should be vertually clear (unless taking vitamin supplements!). During exercise fluid losses should be matched to sweat rate. Obviously, the more you sweat, the more you lose.
Sweat rate is determined by:
- Sex - males sweat more than females;
- Fitness level - sweating mechanisms are better in the very fit;
- Exercise intensity and duration;
- Temperature and humidity;
- Body surface area (the bigger you are, the more sweat you lose);
- Genetics - thank your parents for this one!
On average most people will sweat at a rate of 1 Litre/hour. Fluid replacement should match the rate of sweating which can be measured by loss of body weight during exercise ie. 1 kilogram of weight loss = 1 litre of fluid that needs replacing. Remember, thirst is NOT a good indication of fluid needs.
Latest research indicates that extra salt will not reduce cramping. Cramping has more to do with poor posture, shortened muscle length, very intense exercie and exercise to fatigue, although the exact cause is still not known.
A low sodium intake won't prevent fluid absorption, but consuming sodium in combination with fluid can speed it up. This may be the saving grace against dehydration in those that struggle to meet fluid losses. For ultras and other events over 4 hours, YES, sodium replacement is vital as large amounts will be lost in sweat especially in hot climates (such as ours here in Australia.)
I have outlined below a strategy for those who compete in long distance runs:
- Make sure you're fully hydrated BEFORE the race;
- Check the type of sports drink on offer at drink stations - does it contain sufficient sodium? (and carbohydrate);
- Consume sports drink from early in the race - don't wait until already dehydrated.
- Match your own sweat rates as mentioned above (practise in training first). Remember the hotter the day, the more you will need. This may mean more than one cup per drink station;
- If possible, make up your own drinks. This way you ensure the right concentration. Always make to instructions on the container. Altering concentrations can affect the carbohydrate concentration which will slow down the rate of fluid absorption possibly leading to dehydration.
- If you can stomach it and feel hungry, eat solid food towards end of race. (eg. Sports bar) This will provide sodium and carbohydrate, but remember you MUST drink as well.
- Practice using sports drinks in training .
Fiona Pelly, Cool Running Australia, 11.07.97