Vitamin D, again

When this paper was published Cholecalciferol the basic form of vitamin d3 was thought to be inert inactive and the active forms were calcidiol (the storage form and Calcitriol the hormonal form were the most important.
Circulating Vitamin D3 and 25-hydroxyvitamin D in Humans

We now know better.

Dietary Vitamin D and Its Metabolites Non-Genomically Stabilize the Endothelium
This paper shows cholecalciferol in that basic form is NOT INERT but stabilizes the endothelium and enables the signalling modality that inhibits the production of excess proinflammatory cytokines which only happens optimally when 25(OH)D is at/above 50ng/ml 125nmol/l.

this article explains the way vitamin d inhibits inflammation.
How vitamin D inhibits inflammation — ScienceDaily
and for the nerds here is the science
Vitamin D Inhibits Monocyte/macrophage Pro-inflammatory Cytokine Production by Targeting Mitogen-Activated Protein Kinase Phosphatase 1

the most important thing to note here is that the inhibition of proinflammatory cytokines responsible for excess inflammation only happens optimally when 25(OH)D is at/above 50ng/ml 125nmol/l.

We can only expect our mobile phones to work is the signalling required is present.
Cholecalciferol when in serum in significant measurable amounts enables the required signalling for inhibition of excess inflammatory cytokines.

Unfortunately living modern urban lifestyles, wearing clothes and sunscreen, living in polluted atmospheres within 10km of airports or busy roads prevents sufficient uvb reaching ground level and most people will struggle to get 25(OH)D above 40ng/ml 100 nmol/l
Vitamin D Serum Level by Amount of Sun Exposure

People living at the latitude of the UK usually require in the region of 6000-8000iu extra vitamin d3 daily to get over that 40ng/ml 100nmol/l threshold.
Evaluation of vitamin D3 intakes up to 15,000 international units/day and serum 25-hydroxyvitamin D concentrations

To achieve serum 25(OH)D levels >100 nmol/L on average, required vitamin D intakes of 6,000 IU/d for normal Body Mass Index (BMI), 7,000 IU/d for overweight and 8,000 IU/d for obese.

and that is in Calgary Alberta where they have 1000 hours more sunshine annually than the UK.

Normal vitamin d levels in the UK are shown here.

75nmol/l our peak UK levels at the end of summer is about 30ng/ml in the first image here and at the end of winter our levels are down to just around 35 nmol/l = 14ng/ml

Thanks to the Courtesy of :

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