Sodium
Optimal dose — supplementation not needed.
Although we may not think of salt as a nutrient, it is essential to life.
Sodium is present in sodium chloride (table salt), and is necessary for regulation of blood and body fluids, transmission of nerve impulses, heart activity, and certain metabolic functions. Interestingly, although sodium is needed by animals, it is not needed by plants, and is generally toxic to plants. A completely plant-based diet, therefore, will be very low in sodium.
Sodium ions play a diverse and important role in many physiological processes. It is important for central nervous system function, which depends on the sodium ion motion across the nerve cell membranes. Sodium is the primary cation in extracellular fluids in animals and humans. These fluids, such as blood plasma and extracellular fluids in other tissues, bathe cells and carry out transport functions for nutrients and wastes. Relative loss of body water will cause sodium concentration to rise higher than normal, a condition known as hypernatremia. This ordinarily results in thirst. Conversely, an excess of body water caused by drinking will result in too little sodium in the blood (hyponatremia). The hypothalamus usually works well to cause drinking or urination to restore the body’s sodium concentrations to normal.
In humans, high salt intake has been demonstrated to attenuate nitric oxide production. Nitric oxide (NO) contributes to vessel homeostasis by inhibiting vascular smooth muscle contraction and growth, platelet aggregation, and leukocyte adhesion to the endothelium. Despite this, we forget that salt is supposed to have many of the other minerals present in sea salt. But most salt has had all of the minerals besides sodium and chloride removed. Iodized salt (rarely used in food processing) has a bit of iodine added back in. For home use, we recommend that sea salt be used. I like the Celtic Sea Salt (by Selena Naturally), Hawaiian sea salts, and even the sea salts found at Costco (go for the pink ones).
As an aside, the concept that high salt intake is harmful has been proven to be wrong (except in conditions like heart failure where low salt is needed). Repeated studies have shown that the more salt people eat, the longer they live. A recent large meta analysis in JAMA showed that those who limited salt intake to the government recommended limits were twice as likely to die during the study period than those who exceeded the government limits!
More Information Online
Nutritional primer
We have a 20,000 word primer on nutrition at our website that provides more detail with study references on each nutrient. Click here to visit the "Sodium" section of our primer.