Vitamin D and Gut Flora

GutThere may be a double-trouble issue for us when it comes to Vitamin D.  First is that we are all extremely deficient. The current recommendations to have babies and children take 800 or 1000 IU a day falls short by a long shot for most and will never allow for adequate levels.  Vitamin D3 is the active form, and is really a hormone, not a vitamin at all.  It is formed from cholesterol like many other hormones, and has at least 5 critical functions:

1.  1,25-Dihydroxy D3 (Vit D3) enhances the formation of the enzyme G6PD (glucose-6-phosphate dehydrogenase) which puts a Hydrogen on NADP making the critical anti-oxidant cofactor NADPH. We need NADPH to recycle oxidized glutathione to the useful GSH glutathione.  Glutathione is our most important molecule for oxidative stress.

2.  Vit D3 enhances crystathionine which then forms cysteine.  Cysteine is essential for numerous critical biochemical reactions involving glutathione, taurine, sulfate, metallothionein, oxytocin, or G6PD.

3.  Vit D3 modulates calcium binding and transport proteins that hold calcium in neurons and interneurons, where GABA is a neighbor. These are important functions for network synchrony and proper brain development.

4.  Vit D3 has been shown to have immunomodulatory and anti-inflammatory properties. 

5.  The role of Vit D3 for calcium and bone mineralization is the most known action of this vital hormone / vitamin.

There is a critical vitamin D receptor (VDR) in the intestinal lining. The second issue regarding Vitamin D beyond our typical deficiency involves VDR.  If the intestinal lining is injured (vit D receptors are in the microvilla) the loss of Vit D receptors affects the entire body. The study below shows the relationship between intestinal bacteria and the VDR receptor.


Dr. Paul


  • Angela Gunther

    If the baby can’t take a vit d supplement (she throws it up every time), doesn’t she get vit d through the breast milk? And what is your recommendation for a nursing mother? Does that change by season? Thank you!

    • Paul Thomas, M.D.

      For a baby that throws up the Vit D, I would wonder if a different brand might help. It’s one drop with the brand we carry. If baby somehow still throws up after one drop, then wait and put it in the solid food when the baby starts eating solids around 4 months. No, the breast milk has very little vit D and most moms are severely deficient so they should be taking 5000 IU a day. While someone who is in the sun a lot with clothes off (in bathing suit) in the sumer would not need Vitamin D in the summer, very few of us are actually in the sun that much, so my recommendations do not change by season.
      Dr. Paul

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