Updated: Oct 31
An interesting study across hospital psychiatric patients and dosing. Also alludes to the amount of Vitamin D produced through our skins exposure to sunlight during one day is 25,000 IU :).
"Vitamin D3 is a secosteroid hormone produced in the skin in amounts estimated up to 25,000 international units (IUs) a day by the action of UVB radiation on 7-dehydrocholesterol. Vitamin D deficiency is common due to both lack of adequate sun exposure to the skin, and because vitamin D is present in very few food sources. Deficiency is strongly linked to increased risk for a multitude of diseases, several of which have historically been shown to improve dramatically with either adequate UVB exposure to the skin, or to oral or topical supplementation with vitamin D. These diseases include asthma, psoriasis, rheumatoid arthritis, rickets and tuberculosis. All patients in our hospital have been routinely screened on admission for vitamin D deficiency since July 2011, and offered supplementation to either correct or prevent deficiency. During this time, we have admitted over 4700 patients, the vast majority of whom agreed to supplementation with either 5000 or 10,000 IUs/day. Due to disease concerns, a few agreed to larger amounts, ranging from 20,000 to 50,000 IUs/day. There have been no cases of vitamin D3 induced hypercalcemia or any adverse events attributable to vitamin D3 supplementation in any patient. Three patients with psoriasis showed marked clinical improvement in their skin using 20,000 to 50,000 IUs/day. Analysis of 777 recently tested patients (new and long-term) not on D3 revealed 28.7% with 25-hydroxyvitaminD3 (25OHD3) blood levels < 20 ng/ml, 64.1% < 30 ng/ml, a mean 25OHD3 level of 27.1 ng/ml, with a range from 4.9 to 74.8 ng/ml. Analysis of 418 inpatients on D3 long enough to develop 25OHD3 blood levels > 74.4 ng/ml showed a mean 25OHD3 level of 118.9 ng/ml, with a range from 74.4 to 384.8 ng/ml. The average serum calcium level in these 2 groups was 9.5 (no D3) vs 9.6 (D3), with ranges of 8.4 to 10.7 (no D3) vs 8.6 to 10.7 mg/dl (D3), after excluding patients with other causes of hypercalcemia. The average intact parathyroid hormone levels were 24.2 pg/ml (D3) vs. 30.2 pg/ml (no D3). In summary, long-term supplementation with vitamin D3 in doses ranging from 5000 to 50,000 IUs/day appears to be safe."
My favorite Vitamin D supplement is Quicksilver Scientific Liposomal K2/D3 to ensure excellent absorption along with Magnesium orally, topically, or through epsom salt baths.
A few additional things to consider, the para thyroid regulates magnesium and calcium levels. It needs D, Calcium, B6, Zn, Cu, and Magnesium. [2,3]
 Daily oral dosing of vitamin D3 using 5000 TO 50,000 international units a day in long-term hospitalized patients: Insights from a seven year experience" Patrick J McCullough 1, et. al. Journal Steroid Biochem Mol Biology . 2019 May:189:228-239. doi: 10.1016/j.jsbmb.2018.12.010.Epub 2019 Jan 4. PMID: 30611908; DOI: 10.1016/j.jsbmb.2018.12.010
 Association between serum vitamin B6 concentration and risk of osteoporosis in the middle-aged and older people in China: a cross-sectional study. Jing Wang, et al. BMJ Open. 2019; 9(7): e028129. Published online 2019 Jul 4. doi: 10.1136/bmjopen-2018-028129. PMCID: PMC6615830. PMID: 31278103
 Zinc copper levels in patients with primary hyperparathyroidism. Baylan, et al. Department of Biochemistry, Kahramanmaraş Sütçü İmam University Faculty of Medicine Kahramanmaraş, Turkey. 2 Department of İnternal Medicine, University of Health Sciences Adana City Training and Research Hospital, Adana, Turkey. 3 Department of Endocrinology and Metabolic Diseases, University of Health Sciences, Adana Health Practices and Research Center, Adana, Turkey