What is Vitamin D?
Vitamin D is a fat-soluble Vitamin. It is naturally present in just a few foods. But it can be added to others thus creating fortified foods. It is also available as a dietary supplement. Additionally, Vitamin D is produced when ultraviolet rays from sunlight strike the skin and trigger Vitamin D synthesis. Vitamin D that is obtained from sun exposure, food, and supplements is biologically inert. It must undergo two processes in the body for activation.
The first process occurs in the liver and converts Vitamin D to 25-hydroxy Vitamin D, also known as calcidiol. The second process occurs primarily in the kidneys and forms the physiologically active 1,25-dihydroxy Vitamin D, also known as calcitriol.
| Molecular Formula | C27H44O |
| Chemical Name | (5Z,7E)-9,10-secocholesta-5,7,10(19)-trien-3ß-ol |
| Molecular Weight | 384.64 |
*Source – Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press, 2010.
Why You Need Vitamin D
Without sufficient Vitamin D, bones can become thin, brittle, or deformed. Vitamin D sufficiency prevents rickets in children and osteomalacia in adults. Together with calcium, Vitamin D also helps protect older adults from osteoporosis.
Vitamin D plays various other important roles within the body.They include modulation of cell growth, neuromuscular and immune function as well as the reduction of inflammation. Many gene encoding proteins that regulate cell proliferation, differentiation, and apoptosis are modulated in part by Vitamin D.
Many cells have Vitamin D receptors, and some convert calcidiol to calcitriol.
Am I Getting Enough?
The best indicator of Vitamin D status within the body is serum concentration of calcidiol . It reflects Vitamin D produced cutaneously and also that which is obtained from food and supplements. Moreover, it has a fairly long circulating half-life of 15 days.
In contrast to calcidiol , circulating calcitriol is generally not a good indicator of Vitamin D status because it has a short half-life of 15 hours and serum concentrations are closely regulated by parathyroid hormone, calcium, and phosphate. Levels of calcitriol do not typically decrease until Vitamin D deficiency is severe.
| Serum 25-HydroxyVitamin D [25(OH)D] Concentrations and Health* | ||
| 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) |
*Source – Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press, 2010.
* 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
| Recommended Dietary Allowances (RDAs) for Vitamin D | ||||
| 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) | ||
*Source – Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press, 2010.
* Adequate Intake (AI)
| Tolerable Upper Intake Levels (ULs) for Vitamin D | ||||
| Age | Male | Female | Pregnancy | Lactation |
|---|---|---|---|---|
| 0–6 months | 1,000 IU(25 mcg) | 1,000 IU(25 mcg) | ||
| 7–12 months | 1,500 IU(38 mcg) | 1,500 IU(38 mcg) | ||
| 1–3 years | 2,500 IU(63 mcg) | 2,500 IU(63 mcg) | ||
| 4–8 years | 3,000 IU(75 mcg) | 3,000 IU(75 mcg) | ||
| ≥9 years | 4,000 IU(100 mcg) | 4,000 IU(100 mcg) | 4,000 IU(100 mcg) | 4,000 IU(100 mcg) |
*Source – Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press, 2010.