Dr Rajan Ravichandran, head, The MIOT Institute of Nephrology
Everybody is aware that there is a connection of salt to the kidneys. The word Salt refers to a substance produced by the reaction between an acid and base. But practically refers to Sodium Chloride which we also call as common salt. Salt was discovered 7000 years ago as a preservative. Food would last only if salted. Even now the best preservative for packed food is salt. It can prolong the shelf life for more than 6 months. The offshoot of the original discovery is the use of salt as a taste enhancer. The habit can be addicting and will require to increase the consumption over a period of time to get the same taste. The salt we eat is predominantly removed by the kidneys. Only a small quantity is lost in sweat or stools. As a matter of fact the gold standard test to find out a person's salt intake is to check the 24 hours urine for sodium excretion. Several hundred years back in Chinese medical writing, it was mentioned that high salt intake is associated with thickening of the blood vessels. The association of blood pressure to salt is well known. In tribal people unexposed to salt, the average blood pressure is 90/60. Over generations of salt intake the present normal BP is 120/80. Since kidneys are the end organ to remove salt they get affected in due course. Almost 10% of the adult population have reduced kidney function if sensitive tests are used.
The excess salt not only raises the blood pressure, but also leads to endothelial dysfunction. Endothelial cells line the blood vessels and make up the filtration units in the kidneys. Interestingly, this also leads to increased protein loss in the urine. Higher the protein loss, faster the kidney damage. Almost in any form of kidney disease it is wise to reduce the salt intake. But it is not true that greater the reduction of salt intake better the kidney function. It is necessary to find the optimal intake to preserve the kidney function. Often it is via trial and error method. Increasing the salt intake can increase protein loss in the urine. Some patients with massive protein leak called nephrotic syndrome do very well with complete salt reduction in diet.
Another problem with high salt intake is the formation of kidney stones. Stones normally compose of calcium, oxalate and uric acid. How does sodium
relate to stone formation? The excess sodium while going in the urine drags the calcium leading to stone formation .Of course no topic is now complete without referring to the corona virus. An interesting research paper from Germany recently published showed a correlation of salt intake to the immune system. Higher intake was associated with poor functioning of lymphocytes which is very important to fight the viral disease.
How much salt should we take? The WHO gives a figure of 5gms from all sources -natural, what is added while cooking and what is present in preserved food. This is almost impractical to achieve. People only tend to get disheartened. Other organisations recommend 6 gms, which is a little better.
Then what is a practical answer? Do not assume that you are taking less salt. It is not possible to judge since cultural practices vary and no point in comparing with others. Best solution is to cut down whatever salt you are taking by 25% or at least 10%. This can done by deliberately reducing the salt quantity while cooking, using other spices to enhance the taste, cutting down the intake of packed and processed foods from shelves, eating fresh food when possible and getting rid of the salt shaker from the table. You will be surprised after 2 weeks of trial you will appreciate your food better and start disliking extra salt. Your kidneys are going to be preserved better with this simple tip. The younger you are better is the outcome over years. Children should specially develop the habit of low salt intake.
