Shine Light on Vitamin D

Written by Stephanie Alvarez, Student Dietitian

The sun has always symbolized Vitamin D. Also known as the Sunshine Vitamin, it stands out to be the only nutrient in the vitamin world chemically produced by humans. Vitamin D comes in two major forms – Vitamin D2 (ergocalciferol) and Vitamin D3 (cholecalciferol). Vitamin D2 is primarily found in plant based and fortified foods. Vitamin D3 is synthesized by our skin when exposed to UV-B rays, and found in animal foods, such as egg yolk, liver, and oily fish. Commercial supplements of vitamin D contain either form.1 These compounds are similar in function, but slightly differ in chemical structure. Although called a vitamin, it is more accurate to identify vitamin D as a prohormone. After dermal synthesis from the sun’s UV-B rays, our liver and kidneys convert vitamin D to its active hormone form – calcitriol, a compound similar in chemical structure to that of hormones. Once available, calcitriol aids in calcium and phosphorus absorption. Increasing and maintaining these levels is critical for bone growth and health. Research has found other vitamin D receptors (VDR) in the cell membranes of the immune system, brain, heart and muscle suggesting it plays multiple roles in human health. Multiple studies have concluded vitamin D may play a role in fighting infections, supporting muscular function, preventing the development of cancer, and reducing the risk of autoimmune disorders, such as diabetes or multiple sclerosis (MS).2

Because of its nature, dietitians among other professionalsrealize achieving adequate levels is a challenge. Reports indicate that vitaminD deficiency and insufficiency affect about 1 billion people worldwide.High-risk groups of vitamin D deficiency include age, pregnant women, breastfedinfants, dark skin color people, and those who live in latitudes greater than37° during the winter months when UV-B rays are poor. 3 The classicexample of vitamin D deficiency is rickets. Most commonly diagnosed inchildren, rickets occurs due to an insufficient mineralization of growing bone.This deficiency is characterized by skeletal deformities in the lower limbs. Otherdeficiencies that may result with low vitamin D levels are osteomalacia and anincrease risk of fractures.

The Dietary Reference Intake for those from 1-70 is 600 IU to promote good bone health.4,5 Dietitians and other health professionals should recommend that clients meet their Vitamin D goals by eating food high in Vitamin D such as fortified milk, other dairy products and egg yolks with supplementation, if blood VItamin D level is below normal limits. In terms of sun exposure, 10-15 minutes of midday sun is recommended, however, the amount depends on age, skin pigmentation, season, and clothing.6 The goal is for health professionals to identify those at risk and come up with an individual plan to promote optimal Vitamin D levels.

  1. Institute of Medicine (US) Committee to Review Dietary Reference Intakes for Vitamin D and Calcium; Ross AC, Taylor CL, Yaktine AL, et al., editors. Dietary Reference Intakes for Caclium And Vitamin D. Washing (DC): National Academies Press (US); 2011. 3, Overview of Vitamin D. Available from:
  2. CPE Monthly: Vitamin D – Today’s Dietitian Magazine. Today’s Dietitian. Accessed May 17, 2019.
  3. Pfotenhauer KM, Shubrook JH. Vitamin D Deficiency, Its Role in Health and Disease, and Current Supplementation Recommendations. Journal of the Osteopathic Association. 2017;117(5):301-305. doi:10.7556/jaoa.2017.055.
  4. National Institute of Health.  Vitamin D. Accessed May 30, 2019
  5. Accessed May 17, 2019.
  6. Skin Cancer Foundation. Sun Protection AND Vitamin D – Accessed May 17, 2019.

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