How much vitamin D should you take for a healthy microbiome?

The last post, we found that research had found the vitamin D was the key component for a cascade that influenced B Vitamins, sleep and some digestive issues. This post will try to address the issue of vitamin D dosage.

On my old web site, I had done several posts on Vitamin D (from 2005-2006) – with links to PubMed articles.

In this post, I will jump to the bottom line fast (if you want more detail, see above).

Target Level

  • “The patients with optimal vitamin D status [25(OH)D ≥75 nmol/l]  ” [2016]
  • “Serum iPTH held a stable plateau level at 36 pg/ml as long as serum 25(OH)D values were higher than 78 nmol/l (31 ng/ml), but increased when the serum 25(OH)D value fell below this. ” [1997]
  • “Evidence is reviewed that shows that serum 25(OH)D3 concentrations of < 80 nmol/L are associated with reduced calcium absorption, osteoporosis, and increased fracture risk.” [2004]
  • In my posts from a decade ago, I created this chart using an image from an article from [2004]
Functional indices of vitamin D status and ramifications of vitamin D deficiency.

My suggested target level is 120 nmol/l. 50% above the level that issues start.

How much to take?

This is easy if you know your current level due to a chart from 2004,


Connie M Weaver and James C Fleet, Vitamin D requirements: current and future  
Am J Clin Nutr 2004;80(suppl):1735S–9S

Find the best match in the chart. I will take the high lighted one:

  • Actual reading: 66 nmol/l
  • Chart target: 80 nmol/l
  • Difference: 14 nmol/l
  • Amount to take: 1371 IU
  • So: 1371 IU/14 = 100 IU for each number below. Since our goal is 120 nmol/l, (120-66) * 100 = 5,400 IU/day

A reader indicated their level was 18 nmol/l. this becomes (120-18) * 100 = 12,000 IU/day.

Bottom Line

The numbers above are from the literature assuming no complicating factors such as those listed below. 

In these cases the dosages may need to be up to 10x more.

Any process resulting in malabsorption of intestinal fat may impair the absorption of vitamin D. In one study, absorption of tritium-labeled (3H)-vitamin D in normal subjects ranged from 62.4% to 91.3% of the initial oral dose (10). In patients with celiac disease, biliary obstruction absorption and chronic pancreatitis, absorption fell to 50%, < 28% and < 18% of the oral dose, respectively. In each case, impaired vitamin D absorption correlated with the degree of steatorrhea. Other conditions in which vitamin D absorption is impaired include liver failure (see below), cystic fibrosis, Crohn’s disease, and gastric bypass. Individuals taking bile acid-binding medications (such as colestyramine and colestipol for hypercholesterolemia) will also have impaired vitamin D absorption

Factors Influencing Vitamin D Status (2011)

The proper process is simple: Get your base line, do the computed amount above for 3 months, measure again. According to the literature you should be at the desired level by then. If you are 10% below, increase the dosage by 10%. This is the only way to estimate the degree of malabsorption.