After coming up low on Vitamin D on a blood test, I was once prescribed a Vitamin D supplement (Fultium-D3 20,000 IUs). This was on a rather odd basis - instead of a dose every day, it was a whacking great dose twice a week. In fact, judging by the leaflet, that was the standard way to prescribe it.
Can anybody here think of a medical reason why it would be prescribed that way, or did the manufacturers just think it was more convenient or something? (If so, they were wrong, as it only made it difficult to remember to take it.)

  • Is your possible exposure to sunshine low because Vitamin D is more effective gained from exposure to sunshine- it lasts longer? It might explain something about the dosage because they expect to have some normal sun exposure and the less frequent large dose compensates for its low residence time so the Vitamin D gives you bone enrichment. Commented Jun 14, 2020 at 10:19
  • Probably it was. I'm not sure I follow the logic? Why would something not remaining in the body as long be an argument for taking it less frequently?
    – A. B.
    Commented Jun 14, 2020 at 23:02
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    “High doses of Vitamin D3 therapy may be able to stimulate the VDR and support normal levels of activity, even if you have VDR polymorphisms (14).” Decent overview. info.dralexrinehart.com/articles/nutrition-benefits/…
    – Gordon
    Commented Jul 12, 2020 at 23:30
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    Definitely best to let a doctor manage these higher does, as you did.
    – Gordon
    Commented Jul 12, 2020 at 23:33
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    And from Vitamin D wiki: “Higher gradient (steeper slide) resulting from infrequent dosing results in more Vitamin D getting into the cells.” Again a doctor should always be in charge of these higher doses.
    – Gordon
    Commented Jul 12, 2020 at 23:38

1 Answer 1


Medication can come in not only varying doses, but also the release time can vary. For instance, if you have a painkiller and you want it to work for a long period of time, you can coat it with something so the medicine travels slowly from your GI-tract to your bloodstream. The same goes for vitamin D. What also could be the case, but I'm not sure it applies here, is that you can give a medicine which is actually a "before" molecule. That means that your body turns it into something. So for example pill --> molecule A --> vitamin D. That can take time.In the Netherlands (where I live), all women above 55 can go to their GP for a (free) prescription of a vit-D injection every three months. You can self-administer this by either putting it under your tong or the back of your mouth.


Weggemans, R. M., Kromhout, D., & van Weel, C. (2013). New dietary reference values for vitamin D in the Netherlands. European Journal of Clinical Nutrition, 67(6), 685. https://doi.org/10.1038/ejcn.2013.55

Dutch Ministry of Health. (2011). Response of the Ministry of Health, Welfare and Sport (The Netherlands) on the Discussion Paper on the setting of maximum and minimum amounts for vitamins and minerals in foodstuffs. . The Hague, The Netherlands: Dutch Government.

Traynor, K. (2011). Endocrinologists release vitamin D guidelines. American Journal of Health-System Pharmacy, 68(14), 1276–1277. https://doi.org/10.2146/news110047 Hope this answers your question ;)

  • Rather startling to hear that it's possible to make one that lasts three MONTHS! But it doesn't really answer the question - what I was asking was not how, but why? Is there any medical advantage to doing it at longer intervals, or is it just for the sake of (supposed) convenience?
    – A. B.
    Commented Jun 13, 2020 at 18:08

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