Hey Andy,
Good question. The standard loading dose is based on survey data for the average baseline 25(OH)D serum concentration of 23 ng/mL (57.5 nmol/L) before starting the anti-inflammatory regimen. The following two charts illustrate the normal distribution of 25(OH)D lab results taken before start of regimen and after 30 days from start of regimen including the loading schedule.
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The average 25(OH)D response to a total loading dose of 600,000 IU of vitamin D3 is 60 ng/mL (150 nmol/L) on top of the baseline serum concentration. This figure has been proven by several studies of a single oral loading dose of 600,000 IU of vitamin D3.
Accordingly, that totals per the following... 23 + 60 = 83 ng/mL (207.5 nmol/L), which is also the target serum concentration for a therapeutic response to vitamin D3, i.e., a CH pain free response per the chart above.
Over the last few years, this standard loading dose of 600,000 IU of vitamin D3 spread over 12 days at 50,000 IU/day has worked effectively for most CHers. It also turns out that over time (1 to 3 months) a vitamin D3 dose of 10,000 IU/day results in a stable 25(OH)D serum concentration around 80 ng/mL (200 nmol/L)... The online survey data confirms this figure.
So... for the CHer new to this regimen, see your PCP/GP for a blood draw for the 25(OH)D lab test then start this regimen with the accelerated vitamin D3 loading dose of 50,000 IU/day for 12 days then drop back to the initial maintenance dose of 10,000 IU/day.
Assuming a pain free response or at least a significant reduction in the frequency, severity and duration of CH, the CHer will stay at this maintenance dose for 30 days the go back to his or her PCP/GP for lab tests for serum 25(OH)D, calcium and PTH (Parathyroid Hormone). As long as serum calcium remains within its normal reference range and PTH is in the lower third of its normal reference range, you're good to go at the present maintenance dose and the actual 25(OH)D serum concentration doesn't really matter except as a reference value for a favorable/pain free response.
The answer to why start this regimen with a 12-Day loading schedule is illustrated in the following graphic.
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As you can see, it can take 3 to 4 months for the time course 25(OH)D serum response to a dose of 10,000 IU/day to reach a stable 25(OH)D serum concentration of 80 ng/mL where most of us experience a favorable response to this regimen. As all of us want a pain free response as fast as possible, you can also see that the 12-Day loading schedule elevates serum 25(OH)D to 80 ng/mL in 12 days taking 50,000 IU/day (Total loading dose of 600,000 IU of vitamin D3).
The initial loading schedules were based on spreading the 600,000 IU of vitamin D3 over 2 weeks and 4 weeks. I did this to give our bodies time to respond to these doses by generating the capacity to produce the needed enzymes to hydroxylate vitamin D3 all the way to 1,25(OH)2D3, the genetically active metabolite we need for genetic expression and the down-regulation of CGRP. Both worked very well but took longer than the 12-Day loading schedule... which is equally effective in achieving a CH pain free response. So there's the reason why we need to do the 12-Day vitamin D3 loading schedule.
The above discussion assumes an average response to dose... As you can see that response has a wide variation. This is why some CHers will need to stay on the loading schedule a day or more longer and adjust their maintenance dose upward to 15,000 IU/day.
We've also found that allergic reactions play heck with this regimen's capacity to prevent CH. Accordingly if one is present or suspected, we need a week to 10 day course of a first-generation antihistamine like Benadryl (Diphenhydramine HCL) and a higher vitamin D3 maintenance dose to achieve a favorable response.
Kids and adults under 115 lbs may need a lower vitamin D3 maintenance dose. If the 25(OH)D lab test after 30 days at a stable dose of 10,000 IU/day results in a pain free response, but a 25(OH)D serum concentration above 100 ng/mL (250 nmol/L), then the following rule of thumb dosing guide may be indicated. In this case these CHers need a vitamin D3 dose based on 50 IU of vitamin D3 per pound of body weight per day. Doing the math, a 100 lb adult would need a vitamin D3 maintenance dose of 5,000 IU/day.
This isn't rocket science... If the CH return after lowering the vitamin D3 dose to 5,000 IU/day, bump the dose back up to 10,000 IU/day and make sure to get these lab tests annually.
Of course we need to take all the cofactors and start a healthy diet free of all sugars, wheat products and drink at least 2.5 liters of water a day to ensure that favorable response.
Hope that answers your questions...
Take care and please keep us posted.
V/R, Batch