“Non-essential” nutrients means nutrients that the body can make. Nothing more.
People -even some scientists- take “non-essential” to mean “unimportant.”
Wrong – if we are synthesizing sub-optimal levels of any nutrient, then by definition that nutrient is conditionally essential and must be supplied by the diet or supplementation or medical intervention.
Since there are thousands of nutrients in the body, at thousands of locations throughout the body, most of which are made by the body from other nutrients, including other non-essential nutrients, it is mathematically impossible, impossible, to have optimal levels of thousands of nutrients at all of the thousands of locations within the body. Some will necessarily be in excess here and there and some will necessarily be deficient there and here.
For those in excess, we need to consume less, or more of the nutrients involved in their proper metabolism and excretion. For those in deficiency, we need to consume more, or more of other nutrients involved in their proper absorption and distribution.
Therefore, non-essential nutrients are anything but unimportant.
Re proper location: recall the example of copper deficiency in cytochrome oxidase in the mitochondria of motor neurons (one of many possible routes to ALS?). Motor neurons take up copper considerably more slowly than other cells. Therefore, motor neurons need slow and steady, 24×7, uptake of a proper level of circulatory copper. When copper is deficient in the circulation, these motor neurons can become deficient far more quickly than say liver, which stores copper. Because the chaperone that loads copper onto superoxide dismutase binds copper more avidly than the chaperone that loads copper onto cytochrome oxidase, when copper is deficient in motor neurons, mitochondrial cytochrome oxidase activity suffers more than superoxide dismutase, and cytochrome oxidase deficiency likely increases oxidative stress, which induces superoxide dismutase in a vicious cycle. Whenever superoxide dismutase is induced, the situation becomes even more perilous. So the liver can be replete with copper, the bloodstream can be average to below average in copper for long periods of time, and a single species of enzyme in the mitochondria of a single cell type under the burden of a vicious cycle of oxidative stress can still be deficient in copper, and getting worse as time passes.
This is why the problem of conditionally essential nutrients, in excess or in deficiency in various locals throughout the body, is so vast and so important to health: it is thousands of nutrients times thousands of locations throughout the body. No chance that all of these millions of values are optimal. No chance that all of these millions of numbers are within an acceptable range, for those who are satisfied with mediocre health.