There exists a very weird and unnecessary myth around vitamin C. I have explained this many times in the comments, but I would like to get it right in the post. Vitamin C is L-ascorbic acid. The letter “L” stands for the isomer with the relative configuration L. Naming it “levorotatory vitamin C” probably derives from the fact that L denotation comes from a Latin word “laevus”, which means “left”. However, this is not a sufficient reason to name it levorotatory vitamin C! It constitutes a jumble of notions – relative configuration and optical rotation.
Additionally, differentiation between levorotatory and dextrorotatory vitamin C makes no sense at all. Indeed, ascorbic acid may occur in the form of D-ascorbic acid, however, it is not vitamin C. It stems from the fact, that a different spatial cell structure causes that it does not match the enzymes, transporters, protein receptors, etc. in our body (and at the same time, all other living creatures on this planet). For this reason, it only has a fraction of vitamin C activity, mainly antioxidant functions – free radicals react with ascorbic acid regardless of its spatial structure. It means that D-ascorbic acid is not vitamin C, but it is an anti-oxidant.
All these complicated notions and questions, however, have a very small practical value from a nutritional point of view – at least until somebody starts preaching the supposed superiority of one vitamin C over another. No vitamin C is better or worse, as there is only one vitamin C – L-ascorbic acid (+ its certain derivatives), which may be found in food and supplements. It is not true that there is some “worse, cheap, industrial ascorbic acid”, as the majority of ascorbic acid is produced by means of the Reichstein-Grüssner method from D-glucose (the natural one, as in a sugar bowl) and it is L-ascorbic acid. Theoretically it is possible to produce D-ascorbic acid using the same method from L-glucose, but this glucose isomer does not occur naturally and for this reason it is very expensive to obtain. In other words, synthetically obtained vitamin C is the same as the “natural and real” vitamin C from fruit or vegetables. Yet, it is more beneficial to eat vitamin C with food rather than supplements, as fruit and vegetables also contain a range of other, favorable compounds.
To make this funnier, L-ascorbic acid turns the polarized light (not laser light!)... right. Therefore, in fact, real vitamin C is dextrorotary, which has been experimentally proven. D-ascorbic acid, on the other hand, turns the light left. There is no such vitamin C that turns the polarized light right. In short, the term “levorotary vitamin C” is a nonsense, derived from ignorance, which has been skillfully turned into an empty marketing slogan without any background in the basics of organic chemistry.
In one sentence: There is no such a thing as levorotary vitamin C.
Source: John McMurry, Chemia Organiczna, Polskie Wydawnictwo Naukowe PWN