The US government’s single nutrient requirement for each essential nutrient, with no more variation in the recommended amount other than by age, sex, and body size, and their mistaken idea that all non-essential nutrients have no nutritional requirements (amount required = 0 for all of them) for the maintenance of good health is too narrowly conceived, if not downright erroneous.
Example vitamin C. There are at least three separate nutritional requirements.
Requirement No 1 – the minimum requirement, the amount necessary to avoid scurvy. Roughly 10 mg per day will do, perhaps less.
Requirement No. 2 – the RDA, about 100 mg per day, the amount required to support basic immune and antioxidant functions, and enough to maintain bodily pools at these levels.
Requirement No. 3 – the optimal amount, approximately the amount the body is trying to absorb, which depends on conditions, more when we are sick (such as colds and flus), and much more when we are very sick (such as cancer cachexia). This is the amount needed to keep the body’s mucus flowing smoothly, by thinning the body’s entire lining of mucus, and it is grams per day. It will not prevent a cold, but if you get a cold, you will find considerably more relief from about 3-6 grams of vitamin C a day, as per Requirement No. 3, than from the 100 mg of Requirement No. 2.
Similarly for all other nutrients, both non-essential and essential. If the body makes specific receptors for any nutrient, it is important to health, even if the body already makes a make-do amount. Some adverse consequence, perhaps psychiatric (who notices these, given that moderns are rather crazy to begin with?), and perhaps only distantly related to the shortfall, will ensue, if one does not give the body what it is looking for, and that includes cholesterol, choline, taurine, and non-essential fats.
At least two levels, sometimes three or more, with the optimal level often close to what the body is trying to absorb. An obvious exception: the body is trying to absorb considerably more of certain nutrients like Na+, Cl-, and I-, and the explanation may be in the deep evolutionary past. We must give the body at least the first level of these nutrients, although the body will clearly take up to at least the third level of these nutrients. The optimal level is somewhat short of what the body is trying to absorb.
Similarly for iodine/iodide. While the US RDA of 150 micrograms of iodide is generally enough to keep the thyroid gland functioning properly, it is not enough for breast health, and probably not enough to meet the requirements for brain health and oral health. The body is trying to absorb milligrams of Iodide, and that is nearer the optimum amount. Some experiments of Dr. Guy Abraham suggest that the body will readily absorb nearly 50 mg of an iodide/iodine mixture (since about 45 mg per day is excreted in a 24 hour urine), even when its thyroid is well-supplied with iodide.
As noted above: with NaCl, the body goes after iodide with abandon. No doubt the system evolved under stresses of rather severe deprivation, and this aggressiveness in the absorption of these nutrients is not really necessary when there is such abundance available to us that we have to be sensible in the amount of Na+, Cl-, and I- we give to our bodies.
When 150 micrograms of iodide a day is not enough for thyroid: when a person is overdosed with goitrogens, like F-, Br-, SCN-, ClO4-. For example, some people consume so much bromated white flour products that they have to be dosed with milligrams of iodide a day to compete with Br- for uptake at the sodium iodide symporter and to compete with Br- for oxidation by thyroid peroxidase in the thyroid follicle lumen, along with about 10 grams of NaCl per diem to drive the excess Br- into the urine, as in the protocol of Dr. Guy Abraham. He also uses 3 grams of vitamin C a day to help prevent oxidation of the halide binding site in the sodium iodide symporter (more of a problem when F- and ClO4- are also present at levels that interfere with normal thyroid function).
Note: with Na, Cl, I, and vitamin C, the body is probably not trying to absorb a certain amount or an optimal amount. It is trying to absorb whatever we give it – likely, in a state of nature, we did not give ourselves enough. Now that all of these are readily available, we must be careful not to overdose ourselves.