Vitamin D deficiency changes the intestinal microbiome reducing B vitamin production in the gut. The resulting lack of pantothenic acid adversely affects the immune system, producing a “pro-inflammatory” state associated with atherosclerosis and autoimmunity. 
Three months of vitamin D plus B100 resulted in improved sleep, reduced pain and unexpected resolution of bowel symptoms. These results suggest that the combination of vitamin D plus B100 creates an intestinal environment that favors the return of the four specific species, Actinobacteria, Bacteroidetes, Firmicutes and Proteobacteria that make up the normal human microbiome.
Changes in the levels of certain vitamins from B group under conditions of vitamin deficiency. 1976
- Decreased serum vitamin B12 and vitamin D levels affect sleep quality in children with familial Mediterranean fever.
From the above we see a cascade starting with deficient Vitamin D
- Reduced Vitamin D
- Reduced Thiamine (B1)
- Reduced pyridoxine (B6)
- Reduced Pantothenic Acid (B5)
- eventually reduced Cobalamin (B12)
- ” affect VB12 level, indirectly, by reducing 25(OH)D level in middle aged women. ” 
- Will vitamin D supplementation ameliorate diseases characterized by chronic inflammation and fatigue?  (full text)
- A Review on the Potential Role of Vitamin D and Mineral Metabolism on Chronic Fatigue Illnesses 2016
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.
- “The patients with optimal vitamin D status [25(OH)D ≥75 nmol/l] ” 
- “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. ” 
- “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.” 
- In my posts from a decade ago, I created this chart using an image from an article from 
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
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.
Factors Influencing Vitamin D Status (2011)