Essential Transport Channel - To supply sugar you need sodium, how ironic. Did you know that sodium is the active transport channel for glucose molecule ? Yes insulin lets it in the cells but sodium pumps the molecule physically from the intestinal lumen into the blood. Without adequate sodium there is no primary energy source to begin with for the body. Sodium channels are present where glucose molecule needs to be actively (with help of extra energy and not osmosis) transported into a cell or tissue. While working out or exercising we are recommended a sugar - salt solution for this same reason to aid the immediate uptake of energy and water into the blood.
Rehydration Must have - Thirst is the bad indicator for dehydration and thats because when we feel thirsty our body is actually 3 times more dehydrated than the amount of water that quenches our thirst. When exercising for above an hour or 5 hours like in case of a marathon rehydration should be done every 15- 20 min with a electrolyte - carbohydrate isotonic solution for normal to mildly cold temperature (if the weather is hot & dry / humid). The rehydration solution should have 1.5 gm of sodium per litre water and 1.5 - 6 % of carbohydrate. Simply put for every litre of water add 1/2 tsp of salt and 2 1/2 tsp of sugar or glucose. This solution in 1- 2 glasses (300 - 600 ml) should be ingested 2 hours before a prolonged exercise and sips every 15 min during exercise. Post exercise rehydrate with the solution of at least 500 - 600 ml within first 15 min followed by a carbs- protein meal. Everyone has a misconception that water is immediately absorbed from the intestine into the blood but that is not true. Water is absorbed as per the gastric emptying and the quantity, quality, temperature of the water as well as the activity of the body. If the body is warmed up for exercise or any stress activity gastric emptying will be slowed. What sodium does here is it pulls the water and the glucose from the lumen of the intestine into the blood as its uptake is faster. Of course that does not imply that sodium (salt) should be loaded into a drink as it will hold the water in the lumen causing abdominal cramps. Sodium is a very minor component of water loss due to sweat unlike popular belief and mostly is needed to build up the blood volume and restrict water loss through excretion which is the case if plain water is ingested during and before exercise.
Brain and other vital activity - Sodium is also important for normal neuromuscular transmission and activity. It has a major role to play in the alertness of the brain and muscular tone. The sodium channels present in the axon (nerve ending) of the brain cells are responsible to transmit the nerve charge to conduct the impulse to the muscle or other organ. Same is the case with the muscular contraction and relaxation. Sodium balance extracellularly also controls the brain volume and keeps it maintained at all times. When there is a disturbance in extracellular sodium levels there can be minor to severe neurological problems ranging from headache to disorders. Sodium channels are responsible for all muscular activity along with the calcium channels this includes the vital organ muscles like heart etc.
Blood Pressure & More - Sodium is the major cation of extracellular fluid (water outside each cell) this makes it important for the dehydration and rehydration of every cell in the body. The normal level in blood is 135 - 145 mEq / L. Any change in this range can have massive impact on the entire body primarily the brain. When the level is low it is termed as hyponatremia and the blood volume and therefore pressure decreases due to this as sodium pulls water wherever it goes. When the level is high there is excess of blood volume causing the pressure to rise. The pressure receptors in the blood vessels monitors the levels as well as the receptors in the brain (hypothalamus) that causes the sensation of thirst when the blood volume goes down. Besides the blood pressure & volume changes in sodium levels extracellularly can cause cell damage due to shriveling (dehydration) when sodium level outside the cell is high and pulls the cell water out causing oedema or water retention. If the sodium level extracellularly is less it may swell the cell with excess water thus damaging its normal functions and in case of brain cells causing headaches. Sodium levels in the body are monitored by the Renin- Angiotensin system in the kidney that causes diuretic effect or leads to reabsorption of sodium and water. The kidneys however have a solute threshold of 1400 mOsm/ kg in an adult. If the sodium levels are high enough then the adequate excretion of sodium won't be possible and hence adding up concentration in the blood & thereby kidneys. The nutritional recommendation of sodium through food is 1.7 - 3 gm for an adult which is around 3 - 6 gm of salt. However the western population consumes at least 10 - 15 gm of salt daily and the Asian population around 15 - 20 gm which is beyond the acceptable levels for our body.
FITNESS EXTREME - People give up on salt completely due to medical condition like blood pressure but it is always advisable to monitor your salt intake before stopping it without professional recommendation. There are some who give up on salt for the sake of fitness for eg women to reduce weight and men to reduce water weight for lean cut abs and muscle tone. Male models and actors are known to starve themselves of salt or any food with sodium just before the shoot to show their extremely well chiseled abs but this is highly not recommended practice and instead a low salt intake is a must and replacing raw and natural food to processed food. Women who suffer from weight problems give up on salt completely but the advisable thing to do is cut back on excess added salt and stick to low sodium food which is natural and not processed.
Sodium and salt form a very integral part of our health and fitness but only if used well and not sacrificed or over used.
Wish you wellness.
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