Right, except what if you add salt to your food? Then what? Do you weigh out how many mg of salt you used and then add that to the total? Not exactly. In fact, when was the last time you weighed your salt? It’s more likely that you used a teaspoon or some fraction such as an eighth of a teaspoon to measure your salt.
So how do you know how much sodium is in a teaspoon of salt? I’m going to answer that question using the periodic table of the elements and a little math. If chemistry and math are not your thing, you can skip ahead to the end to find the answer.
First, you have to be aware that sodium and salt are not the same thing. Sodium is in salt, but sodium is not the only thing in salt. Salt is made of two elements, sodium (Na) and chlorine (Cl), and both are present in equal amounts as sodium cholride (NaCl).
Does that mean that 50% of salt is sodium? Well, yes and no. Yes, in that 50% of the atoms in salt are sodium atoms. No, in terms of weight. Why do we care about weight? Because our dietary concerns are with milligrams of sodium, which is a measure of weight, just like pounds or kilograms.
In order to determine the milligrams of sodium in a teaspoon of salt, we need to know how much a sodium atom weighs, how much a chlorine atom weighs, and how much a salt molecule weighs. Then we can figure out what percentage of the weight of salt comes from sodium. Once we know that, and we know how much a teaspoon of salt weighs, we can calculate how many milligrams of sodium are in a teaspoon of salt.
A sodium atom weighs 23 atomic mass units (amu) and a chlorine atom weighs 35 amu. Adding those two together gives you the weight of a salt molecule, which is 58 amu (23 amu + 35 amu = 58 amu). The percentage of sodium by weight in the salt molecule is: (23 amu/58 amu) x 100% = 40%.
If you weigh one teaspoon of salt, you will find that it weighs about 6 grams, which equals 6,000 mg (1 gram = 1,000 mg). Since sodium is 40% by weight of salt, the amount of sodium in one teaspoon of salt is 40% of 6,000 mg, or 0.4 x 6,000 mg = 2,400 mg sodium.
So there are 2,400 mg of sodium in a teaspoon of salt. If you’re limiting your sodium intake to 1,500 mg, as recommended by the American Heart Association, and salt is your only source of sodium, how much does that add up to in terms of teaspoons? If 2,400 mg = 1 teaspoon of salt, then dividing by 8 tells us that 300 mg = 1/8 teaspoon, a convenient and smaller measure. So 5 of those 1/8 teaspoons of salt (5 x 300 mg) is 1,500 mg.
If you’re also having processed packaged foods, use the label to keep track of how much sodium you're getting from those foods and reduce the amount of salt you add accordingly.