Hey Hoppy,
Good question. Taking one D3-50/week works out to an average of 7,100 IU/day. A number of studies found little difference in 25(OH)D3 response to either daily doses of 10,000 IU/day or weekly dosing at 70,000 IU once a week.
A number of us have found the Bio-Tech D3-50 50,000 IU water soluble vitamin D3 has a higher bioequivalence in elevating serum 25(OH)D3 than the same dose of the oil-based liquid softgel vitamin D3 formulations.
No matter the vitamin D3 dose, the time course 25(OH)D3 serum concentration curves all follow the same pattern eventually leveling off as illustrated in the following graphic from a study by Dr. Robert Heaney, MD.
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The reason 25(OH)D3 levels off and doesn't continue to rise is due to a function of calcium homeostasis where cells start expressing 24-Hydroxylase vitamin D3. Calcium homeostaysis is a complex set of mechanisms that control serum calcium concentrations and keep them in a very narrow range.
The 24-Hydorxylase enzyme adds a hydroxyl group [OH] to the 24th position on the vitamin D3 molecule and its metabolites resulting in 24-Hydroxy vitamin D3 a.k.a., 24(OH)D3, 24,25(OH)2D3 and in a few cases 1,24,25(OH)3D3.
The interesting thing about 24-Hdroxylation is these 24-Hydroxylated vitamin D3 metabolites break down rapidly and are either filtered out by the kidneys and dumped over the side in urine or they're filtered by the liver and passed through the GI tract.
Ultimately, the level of 24-Hydroxylation consumes equal amounts of vitamin D3 taken causing an equilibrium in 25(OH)D3, i.e., flattening of the serum concentration curve as illustrated in the above chart.
An example of the higher D3-50 bioequivalence follows. 10,000 IU/day (70,000 IU/week) of the oil-based liquid softgel vitamin D3 results in a mean 25(OH)D3 response of 80 ng/mL while 50,000 IU/week of the Bio-Tech D3-50 results in a mean 25(OH)D3 response of 80 ng/mL.
Here is where the boron in the Kirkland Adult 50+ Mature Multi comes into play. Boron down-regulates the genes that express 24-Hydroxylase. Less 24-Hydroxylase means a higher 25(OH)D3 response. The 150 µg of boron in the Mature Multi is worth an additional 3 to 5 ng/mL response taking one Bio-Tech D3-50 a week. However, if you take 3 mg/day boron with the one Bio-Tech D3-50 a week, the 25(OH)D3 response nearly doubles to 150 ng/mL.
The following chart illustrates lab results of my serum 25(OH(D3, calcium and PTH over the last three years.
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My PCP is very familiar with my vitamin D3 intake and 25(OH)D3 response and has no problem with my 25(OH)D3 this high as long as my serum calcium remains within its normal reference range. As you can see it has.
The other thing to note is I've been taking the Bio-Tech D3-50 at one a week since January of 2019. I've also taken 3 mg Boron at least once a week along with the rest of this regimen daily. As you can see my 25(OH)D3 response has been steady at 150 ng/mL.
I've updated the supplements to include the Methyl Folate + (B complex) in place of the vitamin B 50/100 complex. Rationale: The methylated forms of vitamin B have a higher bioequivalence. I've found this combination gets me through the heavy pollen season without needing to increase my vitamin D3 intake.
Finally make sure you add 3 grams/day vitamin C (1g three times a day) and 30 to 50 mg/day zinc as this is the best immune-boosting strategy we can take to help fight off SARS-C0V-2 virus and the COVID-19 infection. Adding Resveratrol or better yet, the Resveratrol analog, Pterostilbene. It helps zinc enter cells to stop the SARS-C0V-2 virus from replicating.
See my Coronavirus PSA thread for more details.
Take care and please keep us posted.
V/R, Batch