As you probably know, humans are among the minority of animals that require Vitamin C and don't produce it ourselves. For whatever reason (multiple theories exist), we lost the ability. Meanwhile, the vast majority of animals out there that require Vitamin C simply produce it internally, so they have no need for food choices that contain it. Had it not been for the discovery of scurvy as Vitamin C deficiency, we likely wouldn't have ever known that Vitamin C exists at all as a requirement for human health.

Are there known to be cases in other animals of dependence on food containing vitamins that we humans produce ourselves?

  • 2
    $\begingroup$ what a cool question! $\endgroup$
    – uhoh
    Apr 26, 2020 at 8:27

2 Answers 2


The best example I can think of is taurine, which is a non-proteinogenic amino acid.

Taurine is "conditionally essential" for humans1, but essential for cats2,3.


1: Stapleton, P. P., Charles, R. P., Redmond, H. P., & Bouchier-Hayes, D. J. (1997). Taurine and human nutrition. Clinical nutrition, 16(3), 103-108.

2: Knopf, K., Sturman, J. A., Armstrong, M., & Hayes, K. C. (1978). Taurine: an essential nutrient for the cat. The Journal of nutrition, 108(5), 773-778.

3: Markwell, P. J., & Earle, K. E. (1995). Taurine: an essential nutrient for the cat. A brief review of the biochemistry of its requirement and the clinical consequences of deficiency. Nutrition research, 15(1), 53-58.

  • $\begingroup$ @user1136 — Yes and No. Depends on there being a formal accepted definition of vitamin that would exclude taurine. Can you supply one? $\endgroup$
    – David
    Apr 26, 2020 at 9:57
  • $\begingroup$ @user1136 — No. There is an obvious difference between "essential amino acids", which are needed in stoichiometric amounts as components of proteins, and taurine, which although chemically an amino acid is not a constituent of proteins. I don't actually know what taurine is needed for in the body, and a quick glance at the summaries of the papers cited doesn't make this clear, but it does not appear to be an energy factor in nutrition. A key criterion would be the quantities needed in the diet. My impression is that the definition of vitamin is something of a post hoc fudge. $\endgroup$
    – David
    Apr 26, 2020 at 16:54
  • 1
    $\begingroup$ Could you flesh out your answer a little to address the points made by @user1136. I imagine you have a strong case, but it would be good to have it in the open. $\endgroup$
    – David
    Apr 27, 2020 at 17:53

Historically, the vitamin concept arose out of nutritional studies that demonstrated the dietary requirements of additional factors not supplied by a diet of protein, carbohydrate and fats. These substances are 'specific in function' and are required by the body in very small amounts, and were termed vitamins by Casimir Funk (see Hopkins' Nobel Lecture).

One substance that comes very close to being a vitamin for another organism but not for humans is biopterin, although I suspect that the term 'essential growth factor' is more appropriate than 'vitamin', given the current state of biochemical knowledge.

The organism is the protozoan Crithidia fasciculata, which requires the unconjugated pteridine biopterin as growth factor (Patterson et al).

Despite this requirement, and despite the fact that this metabolic need is the basis of an assay for unconjugated pteridines (Dewer and Kidder), no one knows the molecular basis (although there are some suggestions that is it required in pyrimidine biosynthesis) (see Kaufman)

Dewer and Kidder go further and state that "the only organisms at present known to have a dietary requirement for an unconjugated pteridine are members of the flagellate order Kinetoplastida (trypanosomids)" although personally I have never been able to confirm this except for Crithidia. Trypanosomes (the causative agent of sleeping sickness), for example, have never been shown, as far as I am aware, to require an unconjugated pteridine.

Humans, of course, do require an unconjugated pteridine (in the form of tetrahydrobiopterin, or BH4): it is the cofactor for phenylalanine hydroxylase, tyrosine hydroxylase, trytophan hydroxylase, for an enzyme involved in the oxidation of glyceryl ethers, and for nitric oxide synthase (among other roles).

However, it is not a vitamin! We can synthesis it (from GTP, as it so happens). This aspect is discussed in detail by Kaufman, as is the essential role of BH4 in neurotransmitter biosynthesis.

None of the above enzymic systems are known to occur in Crithidia (Kaufman). This organism, for example, cannot convert Phe to Tyr: the only enzymic system, or enzymic systems, capable of converting Phe to Tyr require an unconjugated pteridine (no cytochrome P450 system, for example, is capable of this transformation).

Both plants and E.coli are also of interest.

The evidence for any BH4-requireing enzyme in plants is scant. Plants can synthesise Phe and Tyr (they have the enzymes of the shikimate pathway) but they cannot convert Phe to Tyr. Phenylalanine hydroxylase, for example, has never been isolated from a plant source.

The same applies to E.coli. This organism has no requirement for an unconjugated pteridine and cannot convert Phe to Tyr (see Miller and Simmonds and Kaufman).

But this is not the case for all bacteria. Those, such as Chromobacterium species (ref), that are capable of using Phe as a carbon source have phenylalanine hydroxylase, which requires BH4 (or a closely related pteridine) as cofactor. In these cases, too, the pteridine (BH4?) is not a vitamin but is synthesized de novo from GTP.

Thus, to summarize. The only organism known to require an unconjugated pteridine as a dietary growth factor is Crithidia fasciculata but no one knows why. You and I (as humans) require BH4 as cofactor for key hydroxylation reactions, including the conversion of Phe to Tyr, but it is not a vitamin: we synthesis it. Plants and E.coli have no known requirement for biopterin (or any unconjugated pteridine) and cannot convert Phe to Tyr. Some bacteria, however, do require BH4 (or a closely related pteridine) as cofactor for hydroxylation reactions but these organisms also synthesis it.

  • $\begingroup$ Could you clarify? Is your answer “none”, or just “not pteridine”? $\endgroup$
    – David
    Apr 26, 2020 at 19:22
  • $\begingroup$ OK. That is interesting. I have no specialist knowledge in this area, only a wish to clarify and improve answers to help raise the standard of this site. I feel that we should give a fair consideration to the answer given by @tyresome. It may need expanding, but I don’t think it should be dismissed in a perfunctory manner. $\endgroup$
    – David
    Apr 26, 2020 at 20:28
  • $\begingroup$ This is exactly the type of thing I was looking for! How fascinating that a single species requires a "vitamin" (essential growth factor? tomato, potato) which is either synthesized or unnecessary in every other known organism. Good argument as well $\endgroup$ May 1, 2020 at 15:32

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