Hey Amy,

There can be several reasons why your husband's 25(OH)D response to vitamin D3 dose is low...  At 15,000 IU/day vitamin D3 plus the conutrients: Magnesium, zinc, boron, vitamin A (retinol), Vitamin B complex and vitamin K2 complex your husband should have a serum 25(OH)D up around 90 to 95 ng/mL.

The major factors affecting 25(OH)D response to vitamin D3 dose are:

A chronic inflammatory condition that consumes vitamin D3 as fast as possible will compete for available serum 25(OH)D.

A chronic allergic reaction...  These can be sub-clinical, i.e., no outward or obvious symptoms...

Body mass/weight - The rule of thumb dose is 50 IU/lb body weight/day for normal BMI.

Body Mass Index (BMI) - A high BMI >25 requires 20% to 30% more vitamin D3 than a person with a normal BMI.

Absorption in the GI tract.  There are several GI tract disorders that limit the absorption of vitamin D3.    IBS, Crohn's disease or ulcerative colitis will limit vitamin D3 absorption in the GI tract.

The best course of action if any of these conditions are present or suspected is to have your husband see his doctor for a checkup...

Then take the vitamin D3 using a sublingual application.  In short have your husband pop 20,000 IU worth of vitamin D3 softgel capsules between his back teeth then swirl the contents under his tongue and between his gums and cheeks without swallowing for 3 to 4 minutes.  I do this frequently.  The contents of the gelcaps taste slightly sweet and the gelcaps take on a gummy bear consistency then dissolve completely.

The sublingual application allows vitamin D3 to enter the bloodstream directly through mucus membraines in the mouth.  As this method of vitamin D3 application bypasses the GI tract, giving this a try for a week or two should result in a gain in serum 25(OH)D.  Going in for another lab test of serum 25(OH)D after a couple weeks of sublingual application of vitamin D3 and seeing a gain in its serum concentration will confirm a possible GI tract absorption problem.

The alternative is to take a 50,000 IU/day loading dose for 8 to 10 days.  That should add ~ 30 to 40 ng/mL to his existing serum 25(OH)D concentration, then go in for the 25(OH)D lab test.

As a happy gut is a healthy gut, starting your husband on a course of probiotics might be a great idea...  I take Nature's Bounty Probiotic 10...

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The probiotics will help repopulate friendly colonies of symbiotic bacteria and biota in the gut called the microbiome...  Doing this may help absorption of vitamin D3.

Hope this helps.  Please keep us posted.

V/R, Batch