With heart disease and stroke accounting for over a quarter of deaths each year in Canada, it’s no surprise that a lot of emphasis has been placed on what constitutes a good diet for a healthy heart and circulation. We’ve all heard the advice to reduce our salt intake; many of us who are health conscious have dispensed with a salt shaker and try to cook from scratch as much as we can. However, while this avoidance of salt is beneficial to most people, owing to its potential to lower blood pressure, for those of us who take part in intense and prolonged exercise, being overly cautious with salt could actually do more harm than good. Sodium is lost in sweat, along with smaller quantities of potassium, magnesium, calcium, and urea which we obviously produce more of when we really push ourselves during exercise or take part in endurance activities such as distance running, cycling, and triathlons. If our sodium levels – or indeed levels of any other electrolytes - become depleted, this can be detrimental to our health. Here we consider why a little salt can actually be beneficial when participating in endurance activities.
Sodium as an important electrolyte
Salt is composed of sodium and chloride ions, both of which play an important role in maintaining conditions within the body to promote good health. Sodium is found within all body fluids and not only is sodium crucial to maintain fluid balance, but along with other electrolytes it also preserves nerve and muscle function.
To retain the correct amount of fluid within the body, sodium helps to control the loss of fluid as urine. Specific cells within the kidneys are able to detect if blood pressure changes, which occurs when the amount of fluid in the blood alters. When a drop in blood pressure is detected, a hormone known as aldosterone is secreted. This triggers increased reuptake of sodium, drawing in more water to restore the circulating blood volume.
Body functions and movement are controlled by the nervous system through the conduction of electrical impulses along nerve fibres. The exchange of sodium and potassium ions through the cell membranes of nerves allows the electrical impulses to be produced and to travel to the target area of the body.
Sodium loss through physical activity
During prolonged exercise, if sodium losses are not replaced,
the fall of sodium within the body causes water to move into our cells. As a result, blood volume decreases, compounding water loss through sweating, leading to a fall in blood pressure; this can be accompanied by tiredness, feeling dizzy, an irregular heartbeat, a blurring of vision or fainting. On top of affecting performance, these signs can put your safety on the line. Progression of low sodium results in hyponatremia, where sodium levels drop to critically low levels. When this occurs, the increase of water in body cells causes swelling, which is especially an issue if this happens within the brain; loss of consciousness and seizures are not uncommon and in the worst instances it could be fatal. In the sporting world this is often referred to as "Bonking" or "Hitting the Wall". Muscle weakness is another sign of hyponatremia and not only affects skeletal muscle, but those of the organs, so a cardiac arrest may occur.
If
detected early by means of recognizing symptoms and seeking medical attention,confirmation
of low sodium level through a blood test allows prompt treatment and
a good outcome. However, prevention remains better than cure.
Rehydration to prevent hyponatremia
When you head out to a training session for whichever sport you participate in, you may just take water, as naturally it seems the best way to top up your fluid levels. However, water is not a good choice when taking part in prolonged intense physical activity ( + 90mins), as it has a low content of electrolytes including sodium. If you rely on water in such instances, rehydration won’t be complete and if you drink more water than you require, this can further dilute the sodium in your body. Drinking solely water can therefore increase your risk of developing hyponatremia. The amount and type of fluids used for rehydration purposes remains crucial.
The Dietitians of Canada have provided some guidance on the amount of fluids that endurance athletes should consume before, during and after participation in physical activity. The guidelines state that two hours prior to exercise you should drink 400 to 600ml and then for each 20 minutes of participation to have a further 150 to 350ml of fluid. To determine fluid needs after activity, weigh yourself before and afterwards, taking 450 to 675ml of fluid on board for each pound of fluid lost. However, taking a less scientific approach, if you drink according to thirst, you will ensure that your body receives as much liquid as it needs without over-hydrating.
If you are working out for less than an hour, then you can certainly rehydrate safely using water. However, for longer exercise sessions when you exert yourself more, a sport drink is an appropriate rehydration aid. Don’t forget that you will also lose more sodium in warmer weather, so even though the temperatures in Vancouver may typically be around 22°C in summer, don’t underestimate how much salt you can lose during training. A sport drink usually contains sodium and potassium along with a source of carbohydrate, though other electrolytes such as magnesium and calcium may also be present. It is easy to create a homemade sport drink using water, fruit juice and a pinch of salt rather than relying on commercial products.
While this isn’t an excuse to start being generous with the salt shaker again, if you take part in extended exercise, particularly if it’s warmer than usual, there’s no harm to add a pinch of salt to a meal beforehand or afterwards.
Thanks Eve Pearse for another very informative article.
CH
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