In our previous blog we began a discussion about vitamin D and the wide ranging impact the steroidal hormone has on regulating a multitude of physiological functions necessary for human health. This week we will continue the conversation by describing what vitamin D is and what the recommended healthy levels of vitamin D are per the Institute of Medicine.
What is vitamin D and Why is it Important?
Vitamin D is essentially a steroidal hormone. There are two forms of vitamin D that are important to human health. The first is ergocalciferol or vitamin D2, derived from the ultraviolet exposure of mold or plant-based materials which has limited bioavailability due to its unstable chemical make-up (Houghton & Vieth, 2006). The second is calcipherol or vitamin D3, produced from the photoconversion of 7-dehdrocholesterol in the skin when exposed to UVB irradiation or, obtained through diet and supplementation (Norman, 2008). The vitamin D3 form is further metabolized by the endocrine system to produce 1α,25(OH)2D3, the steroidal hormone that binds to Vitamin D Receptor (VDR) located in our cells (Norman, 2008). These VDR’s are located throughout the cells of almost every organ in our body and according to a study in the open access journal PLOS one, may regulate the expression of up to 1250 genes in the human body, once activated (Hoessein-nezhad, Spira, & Holick, 2013). This is why vitamin D is so important to human physiological function. The expression of these genes affects a broad scope of vital biological functions from calcium homeostasis and blood pressure regulation, to immune system health and brain development. The synthesis of the metabolite 1α,25(OH)2D3 increases the bioavailability of the hormone in the bloodstream which makes the vitamin D3 form far superior than its D2 counterpart.
Recommended Amount of Vitamin D
To measure levels of available Vitamin D in the body, the Institute of Medicine recommends the following blood serum levels of 25(OH)D, to indicate status[i]:
| Table 1: Serum 25-Hydroxyvitamin D [25(OH)D] Concentrations and Health* [1] | ||
| nmol/L** | ng/mL* | Health status |
| <30 | <12 | Associated with vitamin D deficiency, leading to rickets in infants and children and osteomalacia in adults |
| 30–50 | 12–20 | Generally considered inadequate for bone and overall health in healthy individuals |
| ≥50 | ≥20 | Generally considered adequate for bone and overall health in healthy individuals |
| >125 | >50 | Emerging evidence links potential adverse effects to such high levels, particularly >150 nmol/L (>60 ng/mL) |
* Serum concentrations of 25(OH)D are reported in both nanomoles per liter (nmol/L) and nanograms per milliliter (ng/mL).
** 1 nmol/L = 0.4 ng/mL
The recommended daily intake for Vitamin D varies by age as well as environmental factors. The following is the official Recommended Dietary Allowances (RDAs) for Vitamin D as per the Food and Nutrition Board at the Institute of Medicine of The National Academies[ii]:
| Table 2: Recommended Dietary Allowances (RDAs) for Vitamin D [1] | ||||
| Age | Male | Female | Pregnancy | Lactation |
| 0–12 months* | 400 IU (10 mcg) |
400 IU (10 mcg) |
||
| 1–13 years | 600 IU (15 mcg) |
600 IU (15 mcg) |
||
| 14–18 years | 600 IU (15 mcg) |
600 IU (15 mcg) |
600 IU (15 mcg) |
600 IU (15 mcg) |
| 19–50 years | 600 IU (15 mcg) |
600 IU (15 mcg) |
600 IU (15 mcg) |
600 IU (15 mcg) |
| 51–70 years | 600 IU (15 mcg) |
600 IU (15 mcg) |
||
| >70 years | 800 IU (20 mcg) |
800 IU (20 mcg) |
||
* Adequate Intake (AI)
[i] Table taken from: http://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
[ii] Table taken from http://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
Next week we will continue our discussion on vitamin D by examining the best sources of the vital nutrient, important signs to identify vitamin D deficiency, and additional information you can use to optimize your health! Stay tuned…
References
Hoessein-nezhad, A., Spira, A., & Holick, M. F. (2013, March). (R. P. Moray Campbell, Ed.) Public Library of Science, 8(3). doi:10.1371/journal.pone.0058725
Holick, M. F., & Chen, T. C. (2008). Vitamin D deficiency: a worldwide problem with health consequences. The American Journal of Clinical Nutrition, 1080S-6S.
Houghton, L. A., & Vieth, R. (2006). The case against ergocalciferol (vitamin D2) as a vitamin supplement. American Journal of Clinical Nutrition, 694-7.
Norman, A. W. (2008). From vitamin D to hormone D: fundamentals of the vitamin D endocrine system essential for good health. American Journal of Clinical Nutrition, 491S-9S.
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