In a strikingly clear and comprehensive manner, the paper entitled "Central regulation of sodium appetite ," by Joel Geerling and Arthur Loewy of the Department of Anatomy and Neurobiology, Washington University School of Medicine in St Louis, MO, elaborates the mechanisms responsible for our appetite for salt. The physiological apparatus we have evolved over the eons to maintain a fully operational cardiovascular system is largely dependant upon maintaining both a balance and sufficient quantities of the two nutrients most essential to life, water and salt. This fundamental system is can be found in fish, reptiles and all mammals. Life depend on it.
In order for us to survive, our circulatory system must have an adequate volume of blood that is under sufficient pressure to supply all our tissues with the nutrients they need and to remove all the toxic byproducts of metabolism. It is a finely tuned balance of water and salt that allows this to happen. Any amount of water or salt that is consumed in excess of our needs is quickly eliminated through our kidneys. However, an equally important issue is ensuring that we have ingested enough water and salt to make up for any losses we experience. This is where the incredible mechanism controlling the thirst for water and the appetite for salt comes in.
This latest publication shows that this multi-factorial system is so robust and includes so many failsafe mechanisms that it continues to fully function even after large sections of its system are shut down. Employing a complex cascade of physiological functions from powerful hormones, such as aldosterone, to pressure sensitive receptors in the brain, this water thirst and salt appetite mechanism moderates our behavior so that we are driven to quickly replenish the volume and ionic balance of our blood, so that it is pressurized sufficiently for our heart to circulate it through our bodies. When fluids and electrolytes are lost, such as with sweating, physical exertion, diarrhea or other circumstances, we immediately get a water thirst signal. So we drink water to make up the loss. After a delay, our salt appetite kicks in to ensure that the ion levels are replaced. If we don't respond on time to the salt appetite, we die - a situation which was described in an earlier article where a young woman died in a water-holding contest.
It has been repeatedly suggested that policies must be developed to reduce the amount of salt in processed foods. In fact, some countries already have or are in the process of considering policies to effect this. Will these policies be effective? What indication is there that people who are provided with a lower-salt food supply will actually reduce their intake of salt? Based upon this latest publication on salt appetite, individuals faced with foods that are mandated to be low in salt may make up for this in other ways. They may eat considerably more food in order to get more salt or they may simply pick up the salt shaker and add more voluntarily.
The recent publication by as described in a recent article legitimately brings up the question of minimum levels of salt intake. Based upon their data, we can justifiably ask whether the current recommended daily values are prudent. Should the 2,300mg daily upper limit for sodium be reconsidered? Should the Institute of Medicine recommended daily adequate intake of 1,500mg sodium be reconsidered?
Our thirst for water is a basic mechanism we have evolved in our fight for survival. So is our appetite for salt. It is time we realize that the two mechanisms are interdependent and basic to our survival. Any policies promulgated to regulate our consumption of salt must bear this in mind and be based on the most rigorous science. If not, harm will be done.
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