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Thyroid UK
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Vitamin D3 vs D2 advice please?


So it seems my Vit D is chronically low:

VITAMIN D: 17.69 nmol/L - (Range 50.000 - 200.000)

Doc has prescribed Ergoral D2 50,000IU (1,250 micrograms) at one a day for first month then retest. Chemist has had to order these in special as in his words they are "A colossal dose" lol :o

Anyway, I have bought some D3 tablets whilst waiting as have been told far more effective than D2 (I am sure you guys will all agree?)

My question is, should I replicate at same dose or is D3 higher potency so should use less than 50,000IU ?

Many thanks :)

7 Replies


When my vitD was <10 I was prescribed 40,000iu D3 (cholecalciferol) for 14 days followed by 2,000iu D3 daily x 8 weeks and vitD rose to 107. Endo recently checked that I continue to supplement D3 cholecalciferol.

...A review by Houghton and Vieth[13] estimated that cholecalciferol is more than 3 times as effective as ergocalciferol in elevating 25-hydroxyvitamin D and maintaining those levels for a longer time. These authors also note that cholecalciferol metabolites have superior affinity for vitamin D-binding proteins in plasma, relative to ergocalciferol.

In conclusion, ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3) are not bioequivalent and should not be considered interchangeable. Although few head-to-head trials exist, based on pharmacokinetic studies and limited clinical evidence, cholecalciferol is preferred over ergocalciferol. Because of its shorter half-life and decreased potency, this is especially relevant in the setting of severe deficiency, where high-dose ergocalciferol is often only given once weekly. Health professionals should encourage use of cholecalciferol over ergocalciferol in all patients without severe renal failure, either as a general supplement or as a treatment for vitamin D deficiency.



A consultant some years ago told me it should be D3, as D2 didn't do much.

1 like

Hi Davy,

D2 is useless! Why did your GP prescribe this?!?

I take a daily fultium D3 tablet, from prescription, which contains 800mcg of D3.



Hi, no idea but guess as he just a GP knows little about the specifics of Vit D2/D3 :(

I am seeing him again this week, as the tablets/strength he prescribed the chemist cant get lol I can suggest the fultium to him as sure he will be fine with that suggestion.

In the mean time I picked up some Ultra Vit D3 tabs from chemist (only 1000IU/25 microgram) but am throwing them down me like smarties :D


It's a daily dose, on prescription, but one I've been fine on.

You can only absorb so much, so a consistent, & effective dose is best. Take it with fat containing food for best absorption. I have mine with Brazils for selenium, & other nuts. Also a bit of sunshine. (#)


1 like

Pretty useless to give you D2 as it is poorly absorbed and what you need is D3. I use a liquid D3 (oil emulsion - Bio mulsion D forte) which costs about 20 for a year if you are not severely deficient, so you might want to consider that when you are into the Ok range.


Thank you :)


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