Thyroid Hormone and Vitamin A Protect Against Vitamin D Toxicity in Cows

I recently came across several papers published in The Veterinary Record in the 1960s documenting the efficacy and risks of injecting cows with a mega-dose of vitamin D just before calving to prevent “milk fever,” which isn’t a fever at all, but is a mix of clinical symptoms including weakness, loss of appetite, and in the extreme case heart failure. It results from low blood levels of calcium, which sometimes occur in the first few days of lactation, before the cow can adequately adjust its calcium balance to meet the new demands for this mineral. It may be a relatively recent disease resulting from the excessive demand for lactation placed on modern dairy cows. In this post, I will review these papers, which provide evidence that thyroid hormone and vitamin A protect against the harmful effects of the vitamin D injections.

In 1963, JB Tutt published an uncontrolled study showing that nine out of ten cows that had previously developed milk fever remained free of clinical symptoms when injected with ten million IU of vitamin D just prior to calving (Vet Rec. 1963;75:469-70). Tutt did not report the weight of the cows, but we should keep in mind that the body weight of cows can run ten or more times the weight of a typical human, so this dose is very high but not as extreme as it sounds, and its human equivalent is probably close to a single dose of one million IU.

JM Payne soon responded (Vet Rec. 1963;75:848-9) by publishing the results of his own department’s study wherein this dose of vitamin D was not without harm. In this study, the investigators injected cows with either 2.5 million IU, 10 million IU, or 40 million IU. The highest dose produced symptoms of vitamin D toxicity such as excessive urination and loss of appetite, but the cows recovered within seven days. Apart from this, all cows appeared healthy until they were slaughtered seven months later.

Post-mortem examination revealed the cows that received 10 million and 40 million IU were not so healthy after all. Untreated cows and cows given 2.5 million IU appeared normal in these examinations, but those receiving higher doses of vitamin D had extensive lesions in the heart, the aorta and other arteries, and the kidneys. These included pitting and corrugation of the walls of the arteries, widespread calcification, and blood clots at the bifurcations in the arteries and in the heart. The medulla and the tubules of the kidneys were also calcified, with large stones lodged in the renal pelvices, which are the funnel-shaped cavities through which urine exits the kidney into the ureter.

A few years later, Payne published a second report with R Manston showing that vitamin A and thyroid hormone both protect against these effects (Vet Rec. 1967;81:215-6). As in the experiment previously mentioned, while the cows given 40 million IU experienced clinical signs of toxicity including loss of appetite, excessive urination, and even death, those given 10 million IU were free of symptoms. Despite this, 83 percent of them developed extensive calcification of the cardiovascular system and kidneys.

If the cows were also given 100 milligrams of thyroxine (the “T4” form of thyroid hormone) or 5 million IU of vitamin A, the occurrence of these lesions dropped to zero.

Payne’s group also injected cows with 5 million or 7.5 million IU of vitamin D. Two-thirds of them suffered from pathological calcification. Untreated cows and those receiving 2.5 million IU vitamin D did not, but this low dose of vitamin D did nothing to prevent low blood levels of calcium. It was safe, but not effective.

The authors included in the same report several later experiments they conducted using diets that contained less calcium, more phosphorus, and slightly more magnesium. In these experiments, the dose of vitamin D required to produce pathological calcification increased to 20 million IU. Thyroid hormone still proved effective at preventing the calcification, although the investigators did not report additional experiments with vitamin A at this dose of vitamin D. When they experimentally manipulated the mineral content of the diet and the timing of the injections, they found that either increasing magnesium and phosphorus or dividing the dose of vitamin D into several injections could reduce, but not eliminate, the incidence of pathological calcification.

Even though the only treatments that reliably and completely eliminated the pathological calcification were the co-administration of either vitamin A or thyroxine, Payne and Manston concluded that “there seemed to be little point in pursuing this line of work if a ‘natural’ factor was already available awaiting discovery,” by which they meant manipulating the mineral intake of the cows.

As I wrote about in my recent article, “Nutritional Adjuncts to the Fat-Soluble Vitamins,” thyroid hormone directly regulates the expression of matrix Gla protein (MGP), a vitamin K-dependent protein that protects against soft tissue calcification. Normal levels of thyroid hormone also protect rats from blood vessel calcification that would otherwise occur spontaneously in the absence of this hormone. These studies in cows show that greater-than-normal levels of thyroid hormone also protect against soft tissue calcification induced by vitamin D.

In order for MGP to fulfill its protective function, vitamin K must activate the protein by adding carbon dioxide to it. The fact that normal levels of thyroid hormone protect rats from blood vessel calcification suggests that normal levels of this hormone increase the production of MGP in its active form, since inactive MGP would not be protective. The study in question, however, did not measure this directly.

If, as I have hypothesized, vitamin D toxicity leads to soft tissue calcification at least in part because it results in the production of defective vitamin K-dependent proteins, it seems unlikely that thyroid hormone could prove protective simply by increasing the production of MGP. Toxic doses of vitamin D increase the production of MGP between six-fold (cartilage) and 100-fold (lung), depending on the tissue. Research from Tufts University confirmed a critical part of my hypothesis, that calcitriol, the active form of vitamin D, increases the production of MGP in kidney beyond the capacity for vitamin K and its associated enzyme and cofactors to activate it, leading to the production of defective MGP.

If thyroid hormone does nothing more than increase the production of MGP, then extra thyroid hormone should aggravate this situation, yet it is protective. This suggests to me that thyroid hormone also either increases the production of the vitamin K-dependent activation enzyme, increases the production of the enzyme that recycles vitamin K, or that it increases the ability of vitamin K and its associated enzyme to activate the protein by increasing the supply of carbon dioxide.

That vitamin A is protective in cows is consistent with results from mice, rats, turkeys, and chickens, as well a study comparing cod liver oil to vitamin D2 in humans, as I have discussed elsewhere.

Unfortunately, Payne’s group did not report blood levels of calcium, but the fact that the vitamin D was used to improve low blood levels of calcium would seem to suggest that the cows did not have clinical hypercalcemia. If so, this would contradict the common claim that vitamin D must cause hypercalcemia in order to cause soft tissue calcification, but it would be consistent with studies in chickens and hyperparathyroidectomized rats showing that vitamin D causes soft tissue calcification even in the absence of hypercalcemia.

Perhaps the most remarkable point we can take from this study is that the therapeutic dose overlaps with the toxic dose when vitamin D is given alone. While 2.5 million IU was safe, it did not effectively prevent hypocalcemia. Effective doses were toxic.

Such overlap may also be present in human populations, as suggested by a major clinical trial published in 2006 showing that 400 IU of vitamin D and 1000 milligrams of calcium had no effect on the risk of fracture but increased the risk of kidney stones by 17 percent. The population was elderly, and perhaps following recommendations to avoid intakes of vitamin A above the RDA because of research suggesting that vitamin A can aggravate the risk of fracture. The trial, of course, was unable to tease apart the effect of calcium from the effect of vitamin D, but the fact that renal calcification appears to be the most sensitive sign of vitamin D toxicity should give us pause.

If the critical point is the dose of vitamin D, it makes no sense that the therapeutic and toxic windows overlap. If the point is that vitamin D must cooperate with other nutrients, such as vitamin A, and metabolic factors, such as thyroid hormone, such an overlap in the absence of these synergistic partners makes perfect sense.

Read more about the author, Chris Masterjohn, PhD, here.

15 Responses to Thyroid Hormone and Vitamin A Protect Against Vitamin D Toxicity in Cows

  1. Awesome as usual! We may have to look twice regarding the vitamin D hype and be sure to back up any supplementation with blood work. Do you think the usual toxicity threshold for blood vitamin D (around 100 ng/mL) is safe? Or is it possible that the calcification process occurs at lower dose?

    • Hi Laurent,

      Thanks! I think the risk of harm begins at much lower levels than that. I’ve never suggested any such level as a threshold and I can’t understand on what basis anyone would do that.


      • Thanks for your answer Chris! In France, when you ask for a lab test on your serum vitamine D, the optimal “zone” is set between 30 ng/mL and 100 ng/mL, hence my question.

        • Hi Laurent,

          I think having the upper limit that high is pretty reckless. I think harms from vitamin D can come at almost any level of 25(OH)D, in part because the point isn’t how much vitamin D one has in one’s system, but it’s interaction with these other factors, and in part because 25(OH)D is not a specific marker of vitamin D status. I plan to write a blog series on that latter point soon. All that said, I think the risk of harm becomes much higher when you get past 50 ng/mL, which is where you start to see some specific ill effects in the epidemiological literature, such as bone resorption. Total mortality is lowest at a considerably lower 25(OH)D as well. So I think the main focus should on getting all the synergistic partners. As a secondary point, I think 30-50 ng/mL is a much safer range than 30-100. I see no reason to push25(OH)D above 50 ng/mL unless someone has a genetic resistance to vitamin D of some sort.


  2. Norm Haight says:

    Thanks so much for providing us all with a front row seat to your cutting-edge research. Just from observing the people close to me, it sure appears that vitamin D supplementation is becoming imbalanced.

    I’m interested in how a person can have access to better nutrition in a cost-effective way and have been making sauerkraut and raw milk kefir, mainly for their probiotic benefits. I’d like to quantify and possibly enhance my efforts from a vitamin K2 standpoint and am wondering if you think it’s practical, cost wise, to have some individual foods tested. If so, please recommend a lab.

    I’ve been involved with market gardening for several years and would enjoy seeing firsthand the affects that changing soil fertility, season and various fermentation processes have on nutrition, particularly the various isoforms of vitamin K2.


    • Hi Norm,

      I’m glad you’ve found the writings helpful. Setting something up “in-house” for testing fat-soluble vitamins in foods is a major goal for WAPF right now, but I anticipate that taking another year or two to get going. Currently I don’t have a specific lab to recommend, but I would recommend using a lab that is very upfront and open about their methods/testing protocol.


  3. Travis Culp says:

    Thanks for the work, as always.

    I’ve found that, for myself at least, 2-3000IUs of D3 maintains my sun-induced summer 25(OH)D level of 40-50ng/mL. It would appear that the body uses about that much per day. If my cursory research is correct, the body also uses about 4-5000IUs of vitamin A per day, so I’m fairly certain this dose would maintain a desirable serum level.

    The only problem is that I have no idea what a desirable serum level is. If we move vitamin D higher in the acceptable range, do we then need to do the same to A? I wonder if something like 80µg/dL is desirable in that case. Have you ever come across anything that might indicate what an optimum level is?

    As far as I can tell from the cancer incidence studies, around that level appears to be desirable without much in the way of vitamin D. It would seem that in the absence of vitamin D sufficiency, one has to choose between cancer and fracture.

    • Hi Travis,

      Vitamin A blood levels seem to be less related to vitamin A status outside of extreme deficiency or excess than 25(OH)D is to D status. I’ll try to write more about this in the future though.

      Thanks for your comments,

  4. Wilfrid says:

    Hi Chris,

    Why don’t using vitamin A/D/K on skin rather than by mouth?
    It should at least minimize largely the toxicity.
    I think that the work of Sobel and Al on transdermal vitamin therapy could justify that kind of utilisation for liposoluble vitamins.

  5. Wilfrid says:

    I would like to add that of course absorption would be less efficient….
    But using around 50000 UI of A with 20000 UI of D and around 5mg of K will probably be a safe bet and more safe in the long run.


  6. Count Iblis says:

    The question is then how high calcidiol levels would interfere with the processes that are regulated by calcitriol, which are tightly controlled. If I read this paper:

    I don’t get a lot concerned with my intake of about 7000 IU/day and my calcidiol level of around 200 nmol/l. It could be that problems start to occur on the long term in the gray area between 250 nmol/l and 750 nmol/l, but I find it difficult to understand how natural levels of 250 nmol/l or lower could be dangerous.

    We have to also consider that until very recently not a lot was known about natural calcidiol levels. While one could have known that the 10,000 IU/day that you can naturally get from the Sun suggests that 150 nmol/l is more natural than, say, 50 nmol/l, the medical establishment was still surprised by this result:

    And later the same team performed more such measurement, they even found a pregnant women with a calcidiol level of 263 nmol/l.

    Thing is, after her baby is born, her baby gets enough vitamin D via her breast milk, while here in the West, we need to give our babies vitamin D supplements.

    • The epidemiological evidence suggests that harm, such as bone resorption, kidney stones, and heart disease, might occur at levels considerably and in some cases far less than 250 nmol/L. Same for total mortality. The sun does not provide 10,000 IU/day. It may for a single dose for the first day in an unexposed person with light skin, but long-term studies suggest that people with very high sun exposure have levels closer to what someone would get from supplementing with something closer to 3,000 IU for the coldest six months of the year in a temperate area. I’ll be blogging about this a bit more in the future. In any case, thank you for your comments.

  7. Spokes says:

    Interesting article. I use vitamin D3 supplementation, it’s been very effective in managing some of my mental health issues (I can’t rule out placebo, but it’s worked better than other things I also believed would work). It’s not like I get a lot of sun, but I became more cautious of it’s use because of headaches. I will remain cautious of its use, especially after this examination of the stuff, but I will also consider it in more in the context of other factors. I did try a cod liver oil purported to contain A and D in good ratios, but I didn’t get on well with that at all.

  8. Alex Lorin says:

    I have recently been diagnosed as having hypothyroidism as well as a vitamin D deficiency (as well as an iron deficiency). Since I have been on supplements and Synthroid I can say that my mood and general state have improved. I will be sure to stay up on blood testing and watch for other changes. Thanks for the interesting (and maybe a little above me) read.

  9. Peter K. says:

    Great synopsis and discussion. Thanks! There has been some really good Published reports by Dr Bruce Ames that show how Vitamin D deficiency is linked directly to Autism, ADHD, and many other Psylogocal conditions.

    Please See: Vitamin D hormone regulates serotonin synthesis. Part 1: relevance for autism
    By Dr. Bruce Ames

    Part 2: Vitamin D and the omega-3 fatty acids control serotonin synthesis and action, part 2: relevance for ADHD, bipolar disorder, schizophrenia, and impulsive behavior.
    By Dr. Bruce Ames

    There was also a fascinating study at the Linus Pauling Institute at the University of Oregon about How Vitamin D along with Pterodtilbene or Resveratrol dramatically activated the immune System more than 444 other compounds.

    Here is a page with almost everything you could want to know about Vitamin D from The Linus Pauling Institute:

    My Question is what would be the most balanced way to take 2000-5000 IUs of Vitamin D3 per day? With Vitamin A, Calcium, Magnesium, and Vitamin K?

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