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Nakahara et al write in Identification of Vitamin L1 (Anthranilic Acid):

In 1934, we demonstrated for the first time the existance of a specific dietary factor of lactation, since designated vitamin L1, and the progress made in our investigation on the subject has been communicated to the Imperial Academy from time to time.

Thus in 1936 we reported that there exists in addition to vitamin L1 a second factor necessary for lactation (vitamin L2), and later showed that yeast nucleic acid has the action of this second factor.

Is the claim that L1 and L2 are necessary for lactation and thus vitamins true? Wikipedia says there's evidence that it isn't. Wikipedia cites an article by Michael W. Davidson of the Florida State University that itself itself lacks sources.

  • This seems non-trivial to find a good answer for. My guess as to why is because of how old it is. So far I've mostly seen things like the article you linked to that just says "Later studies have confirmed that neither of these factors are essential to lactation either in rats or in humans." – Rob Watts Apr 6 '16 at 20:49
  • @RobWatts : Its not simply that it's old. A bunch of relevant literature seems to be in Japanese. But you are right that it seems non-trival. That's why I put the bounty on it ;) – Christian Apr 6 '16 at 21:41
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The work of Nakahara et al. concerning vitamins L1 and L2 being essential for lactation is considered refuted in the sense that others found multiple generations could be bred living on diets that are deficient of vitamins L1 and L2.

See Milk: the Mammary Gland and Its Secretion, volume II at page 171 which cites to the following article as an example:

Lactation and Reproduction on Highly Purified Diets Nature volume 150, page 318 (12 September 1942)

NAKAHARA et al.[reference 1] have claimed the existence of specific lactation vitamins, factors L1 and L2 ; they state that, if these are missing from the diet, rats will reproduce but not lactate. We [reference 2] used a diet which was unlikely to contain these factors, but failed to confirm the finding of the Japanese workers. The recent report, by Rogers et al. [reference 3], of the successful rearing of two generations of mice on a highly purified diet is of obvious interest in this connexion. We therefore think it opportune to report on experiments of our own in which three generations of rats have so far been born and reared on highly purified diets.

So both Folley et al. and Rogers et al. reported that rats can lactate enough for generations to reproduce without vitamins L1 and L2.

  • Perhaps I don't understand correctly, but a diet deficient in "L vitamins" is not necessarily evidence that they are not necessary nutrients. It could mean that the body can synthesize them on its own, making them hormones or something, much like cholesterol, or like how we all thought Vit D was a vitamin at first, but we now know it is actually a hormone. Shouldn't the gold standard here be "L vitamin" blood tests on rats that produce milk successfully and rats that do not then make a comparison of the results? – fredsbend Apr 7 '16 at 21:09
  • @fredsbend if you take the Wikipedia definition of "vitamin" which is "An organic chemical compound (or related set of compounds) is called a vitamin when the organism cannot synthesize the compound in sufficient quantities, and it must be obtained through the diet" then vitamin D "is not strictly a vitamin" (unless there is no sunlight). en.wikipedia.org/wiki/Vitamin_D and in that sense the deficient diet shows L1 and L2 are not vitamins by that definition of vitamin en.wikipedia.org/wiki/Vitamin – DavePhD Apr 7 '16 at 21:28
  • The question is not about how to categorize these compounds but whether they are necessary for rats to lactate, whether they are proper vitamins or not. The reason we call Vitamin D a vitamin is because medicine didn't realize that we synthesize it until decades after its discovery. I don't know anything about L1 and L2, but saying they are not needed for lactation just because they are not present in the diet is a false conclusion. The rats may be able to synthesize them, so a proper test to see the impact of L1 and L2 on lactation should include blood tests. – fredsbend Apr 7 '16 at 21:37
  • Or, what first needs to be done is testing to show that rats do not synthesize L1 and L2. A control group, an L1 L2 diet deficient group, and an L1 L2 diet rich group, then blood or urine testing. – fredsbend Apr 7 '16 at 21:42
  • @fredsbend I only answered the "and thus vitamins" question in the body of the claim. I didn't answer whether or not rats need to synthesize L1 and L2 themselves in order to lactate. – DavePhD Apr 7 '16 at 21:45

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