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Vit D3 levels/measurement


Some useful information here on different measurements used for assessing D3 status. Understanding the difference between nmol/L and ng/ml is important... see the link below for a conversation factor.


If appropriate, doctors can test the levels of Vitamin D (or 25(OH)D), in the blood. When receiving results, knowing which unit of measurement, ng/mL or nmol/L, the blood levels have been measured in is important. In most countries, vitamin D levels are measured using units called nanomoles per litre or nmol/L. In the US and a handful of other countries, levels are measured using nanograms per millilitre or ng/mL.

The two differing units of measurement are much like metric vs imperial and this can lead to confusion about the results. To convert ng/ml to nmol/L multiply the ng/ml by 2.5 for example 50 ng/ml is equivalent to 125 nmol/L."

Hi Sandy,

Thanks for posting this;it is very useful and perhaps very timely as winter is approaching and we have much less UV light to take in outdoors.

At the beginning of the year I was found to be deficient in Vitamin D but due to supplements and lots of sun my present score is up to 60 nmol/ L which apparently is the bottom end of the sufficient range-my specialist advised me yesterday  to double my intake as it is winter;he said that in a Covid era  a score between 70 and 100 is an ideal level for me.My bloods printout has a note saying if your score is over 200 nmol/L consider reducing the dose.

Another measure that did use to confuse me in terms of dosing is the relationship between IU:international units and ug or mcg:micrograms . I try to think in IUs but for reference on my package of pills it says each tablet of VitaminD (as D3 1000 IU) is equivalent to 25ug/mcg. I believe for someone over 70 the RDA -recommended daily allowance is at least 800 IU.I am going to take from now on 2000 IU each day as per medical advice.

It is surprising how so many foods even meat and chicken and lots of fruit and veg do not contain very much Vitamin D or none at all;apart from the pills and a few foods like fish ,some mushrooms and dairy products, cod liver oil has the highest concentration of D if you can swallow it!

Am I correct that Vitamin K and Vitamin C either as supplements or as foods  help us to absorb D better?

With best wishes


Hi John,

I maintain my vitamin D level around 170 nmol/L. - which is equivalent to 70 ng/ml.

60 nmol/L is insufficient for viral and cancer protection. Here is a handy conversion tool:

To get to my target range I take 5,000 IU's vitamin D3 every day in summer and 7500 IU's every day in winter (5,000/10,000 alternating).

Vitamin D requires fat metabolism to absorb. Best to take a vitamin D supplement while eating food which has some fat (avocado, cheese, etc.).

Vitamin K2 (not to be confused with K1) works with vitamin D in calcium mobilization and overall health of the immune system as well.