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Selvi and Florencia. Both of us are pharmacists. We enjoy writing since college.

Vitamin D, The Sunshine Vitamin

The sunshine vitamin is also a name to refer to vitamin D because the sun produces mainly vitamin D on the skin. However, the sun is not the only source, but food can be a source of vitamin D too, namely fish liver, cereals, and oily fish. ​1–3​

Vitamin D is one of a fat soluble vitamin that can also available as a supplement.​4​

Vitamin D Metabolism

Vitamin D, The Sunshine Vitamin

Pic from https://www.precisionnutrition.com/all-about-vitamin-d

Skin responses to sunlight and creates vitamin D at outdoors. Vitamin D has various forms; the animal form and the plant form. Cholecalciferol or vitamin D3 is the animal form, and ergocalciferol or vitamin D2 is the plant form. ​1,4​

However, vitamin D3 should be modified to an active form of vitamin D, which is 1,25-dihydoxyvitamin D3 [1,25(OH)2D3].​3​

The sun emits two types of ultraviolet (UV), which is UVA and UVB. Ultraviolet B (UVB) exposure in the skin alters sequential 7-dehydrocholesterol (7-DHC) to pre-vitamin D3 and vitamin D3. The next step, the sources of vitamin D from sun and food bind to vitamin D-binding protein (VDBP) in the liver. Next, vitamin D undergoes hydroxylation reactions in the liver to form 25 hydroxyvitamin D [25(OH)D], also known as calcifediol using cytochrome 450 enzymes (CYP). ​3–5​

After that, calcifediol is transported to kidney and CYP enzymes hydroxylate it to form an active form, 1,25(OH)2D3, is also called calcitriol. ​3,5​

Calcitriol is lipophilic, so it can transverse cell membrane into the nucleus. In the nucleus, calcitriol binds to vitamin D receptors (VDR). Thus, it maintains calcium and phosphorus homeostasis in the body.​2,3,5,6​

Vitamin D Receptors

Vitamin D receptor (VDR) is a member of nuclear receptor (NR), a ligand-dependent transcription regulator molecule that binds to 1,25(OH)2D3 with high affinity and high selectivity.​3,7,8​

VDR present in cells of the intestinal epithelium, parathyroid gland cells, renal tubules, muscle, eyes, brain, pancreas (beta islet cells), pituitary gland, skeleton (osteoblast and chondrocyte), and also immune system (monocytes, macrophages, and T-lymphocytes). The highest are chiefly in the intestine, kidney, parathyroid gland, bone, and tissues that have roles in maintenance of calcium homeostasis.​2,5​

VDR interacts with vitamin D response elements (VDRE) (specific DNA sequence elements) on vitamin D-regulated genes. VDRE comprise two hexameric nucleotide half-sites. Furthermore, it accommodates the interaction between VDR with retinoid X receptor (RXR) to form a heterodimeric complex. This interaction induces transcription of many genes.​3,5,8,9​

Vitamin D Functions

Vitamin D maintains calcium and phosphate homeostasis. Clearly, these nutrients help to keep bones, muscles and teeth healthy. Moreover, keeping bones strong and healthy, prevent osteoporosis and losing bone density that lead to fractures. Vitamin D also act as modulator that help regulate the immune system and the neuromuscular systems. In the immune system, it reducing the risk of flu, microbial infection and respiratory inflammation. Also, keeping an adequate level of vitamin D may reduce the risk of depression.​2,3,5,10–13​

Vitamin D Deficiency

Vitamin D deficiency means that our body does not have enough vitamin. Calcifediol is the primary form of vitamin D in circulation and its serum level is used to show vitamin D status of someone. Its concentration of 10 ng/mL (25 nmol/L) is considered as a cut-off for determining the lower limit of adequacy. ​3,14​

Vitamin D Deficiency Causes

This condition can occur because of several reasons. ​1,13,14​

  1. Minimal sun exposure. If you have darker skin or using a sun protection factor (SPF) 30 or clothing that covering skin can reduce the ability of skin to absorb the UVB rays. Also, people who live in a location that exposure to sunlight is limited.
  2. Liver or kidney cannot convert vitamin D to its active form.
  3. Having not enough absorption of vitamin D from digestive tract.
  4. Lower intake of vitamin D than recommendation.
  5. Obesity, body fat binds to vitamin D and prevents it to circulate in body.
  6. Breastfeeding. Infants who breastfeed need a vitamin D supplement because human milk is a poor source of vitamin D. The American Academy of Pediatrics recommend 400 international units (UI)/day of oral vitamin D for infants.

Vitamin D Deficiency Effects

Vitamin D deficiency brings to some effects to several health conditions. It leads to a loss of bone density, which is it may contribute to osteoporosis and fractures. It can cause rickets in children. Rickets is a rare disease, this condition causes bones to become soft and bend. In adults, it leads to osteomalacia. Osteomalacia resulting in weak bones, bone pain, and muscle weakness. ​1,13,14​

Furthermore, it also associated with several conditions including high blood pressure, diabetes, infections and immune system disorders, and multiple sclerosis.​13​

Vitamin D Sources

Sun Exposure

Ultraviolet B (UVB) from the sun has wavelength 290-320 nanometres. It penetrates skin which uncovered with clothing or sunscreen. Furthermore, it converts 7-DHC to pre-vitamin D3 and the vitamin D3. In addition, UVB rays does not penetrate glass, thus sun exposure through the window does not produce vitamin D.​1,15,16​

It has been suggested, outdoors sun exposure for 5-10 minutes between 10.00 and 15.00 at 2 or 3 times a week to the face, arms, hands, legs, or back lead to adequate vitamin D synthesis. Nevertheless, when in outdoors more than time that has been recommended, wearing protective clothing and applying a sunscreen with SPF 8 or more, and stay hydrated for sure. Above all, some factors may reduce the production of vitamin D3, for instance, skin pigmentation, aging, and application of sunscreen.​1,15,16​

In Indonesia, some studies showed low UVB intensity at 07.00 and increasing until 11.00. After that, the UVB intensity is stable until 14.00 and then decreasing. UVB intensity at 16.00 is the same as at 07.00. They showed sun exposure for approximately 15 minutes at 11.00-13.00 or 25 minutes at 09.00 at 3 times a week can improve vitamin D level.​17,18​

Foods

There are some foods that naturally have vitamin D, such as fatty fish including tuna, salmon, mackerel, cheese, mushrooms, beef liver, egg yolks, fortified cereals and juices, and fortified milk. In particular, for fortified food, check the food label first to find it contains vitamin D or not.​1,13,14​

Dietary Supplement

Vitamin D dietary supplement has two different forms, D2 and D3, these vitamins increasing vitamin D level in the body. D2 is produced by the UV irradiation of ergosterol in yeast. D3 is produced by 7-DHC irradiation from lanolin and cholesterol chemical conversion.​1,19​

Recommended Dietary Allowance (RDA) of Vitamin D

RDA is an average daily of adequate intake to meet the nutrient requirements of almost (97-98%) healthy individuals. It is often used to plan nutrients diets for someone. ​1​

Micrograms (mcg) or international unit (IU) is an RDA measure for vitamin D. Also, the biological activity of 1 mcg of vitamin D is equal to 40 IU.​1,13,14​

The recommended dosages of vitamin D are:

  • 0 – 12 months: 400 IU (10 cmg)
  • 1-13 years: 600 IU (15 mcg)
  • 14-18 years: 600 IU (15 mcg)
  • 19-50 years: 600 IU (15 mcg)
  • 51-70 years: 600 IU (15 mcg)
  • 71 years and older: 800 IU (20 mcg)
  • Pregnant and breastfeeding women: 600 IU (15 mcg)

Otherwise, people may need more if they at high risk of vitamin D deficiency.

Excessive Consumption of Vitamin D

Excessive consumption of vitamin D over a lengthy period can cause high calcium level in the body, known as hypercalcaemia. It leads to the hardening of kidney, heart, lung and blood vessels.​13,19​

Getting too much vitamin D causes toxicity and the symptoms, such as vomiting, nausea, loss of appetite, a metallic taste, dry mouth, diarhea, and constipation. Therefore, some professionals suggest to not take up to 10,000 IU/day. The National Institute of Health explained taking 10,000 IU/day of vitamin D out of the question show symptoms of toxicity. On the other hand, if taking 10,000 IU/day oral for over 6 months, may be harmful. ​4,13,14,19​

Surprisingly, excessive sunlight does not lead to vitamin D toxicity.​1,4​

References

  1. 1.
    Vitamin D. National Institutes of Health. Accessed June 9, 2020. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
  2. 2.
    Wang Y, Zhu J, DeLuca HF. Where is the vitamin D receptor? Archives of Biochemistry and Biophysics. Published online July 2012:123-133. doi:10.1016/j.abb.2012.04.001
  3. 3.
    Hughes DA, Norton R. Vitamin D and respiratory health. Clinical & Experimental Immunology. Published online October 2009:20-25. doi:10.1111/j.1365-2249.2009.04001.x
  4. 4.
    Andrews R. All About Vitamin D. Precision Nutrition. Accessed June 9, 2020. All About Vitamin D
  5. 5.
    Teymoori-Rad M, Shokri F, Salimi V, Marashi SM. The interplay between vitamin D and viral infections. Rev Med Virol. Published online January 6, 2019:e2032. doi:10.1002/rmv.2032
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    Pike JW, Meyer MB. The Vitamin D Receptor: New Paradigms for the Regulation of Gene Expression by 1,25-Dihydroxyvitamin D3. Endocrinology and Metabolism Clinics of North America. Published online June 2010:255-269. doi:10.1016/j.ecl.2010.02.007
  7. 7.
    Kongsbak M, Levring TB, Geisler C, von Essen MR. The Vitamin D Receptor and T Cell Function. Front Immunol. Published online 2013. doi:10.3389/fimmu.2013.00148
  8. 8.
    Dowd DR, MacDonald PN. Vitamin D Receptor. In: Encyclopedia of Biological Chemistry. Elsevier; 2013:540-544. doi:10.1016/b978-0-12-378630-2.00396-0
  9. 9.
    Pike JW, Meyer MB, Lee S-M, Onal M, Benkusky NA. The vitamin D receptor: contemporary genomic approaches reveal new basic and translational insights. Journal of Clinical Investigation. Published online February 27, 2017:1146-1154. doi:10.1172/jci88887
  10. 10.
    Eyles DW, Smith S, Kinobe R, Hewison M, McGrath JJ. Distribution of the Vitamin D receptor and 1α-hydroxylase in human brain. Journal of Chemical Neuroanatomy. Published online January 2005:21-30. doi:10.1016/j.jchemneu.2004.08.006
  11. 11.
    The Benefits of Vitamin D. healthline. Published April 7, 2020. Accessed June 10, 2020. https://www.healthline.com/health/food-nutrition/benefits-vitamin-d
  12. 12.
    Anglin RES, Samaan Z, Walter SD, McDonald SD. Vitamin D deficiency and depression in adults: systematic review and meta-analysis. Br J Psychiatry. Published online February 2013:100-107. doi:10.1192/bjp.bp.111.106666
  13. 13.
    Ware M. What are the health benefits of vitamin D? Medical News Today. Published November 7, 2019. Accessed June 10, 2020. https://www.medicalnewstoday.com/articles/161618
  14. 14.
    Vitamin D Deficiency. Medline Plus. Accessed June 10, 2020. https://medlineplus.gov/vitaminddeficiency.html
  15. 15.
    Dawodu A, Kochiyil J, Altaye M. Pilot study of sunlight exposure and vitamin D status in Arab women of childbearing age. EMHJ. 2011;17(7):570-574. http://www.emro.who.int/emhj-volume-17/volume-17-issue-7/article3.html
  16. 16.
    Tangpricha V. Vitamin D Deficiency and Related Disorders Treatment & Management. Medscape. Published October 29, 2019. Accessed June 10, 2020. https://emedicine.medscape.com/article/128762-treatment#d1
  17. 17.
    Setiati S. Pengaruh Pajanan Sinar Ultraviolet B Bersumber dari Sinar Matahari terhadap Konsentrasi Vitamin D (25(OH)D) dan Hormon Paratiroit pada Perempuan Usia Lanjut Indonesia. JKMN. 2008;2(2):147-153. https://media.neliti.com/media/publications/39563-ID-pengaruh-pajanan-sinar-ultraviolet-b-bersumber-dari-sinar-matahari-terhadap-kons.pdf
  18. 18.
    Yosephin B, Khomsan A, Briawan D, Rimbawan R. Peranan Ultraviolet B Sinar Matahari terhadap Status Vitamin D dan Tekanan Darah pada Wanita Usia Subur. JKMN. 2014;8:256-260. https://media.neliti.com/media/publications/39610-ID-peranan-ultraviolet-b-sinar-matahari-terhadap-status-vitamin-d-dan-tekanan-darah.pdf
  19. 19.

Selvi Megawati

Pharmacist. Part of wethinkweshare team. I enjoy writing and sharing about pharmacy and health. I hope you have much information from this website. 

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