Essay on Vitamin D and its deficiency

Authors Avatar by johnleung2000s (student)


Vitamin D is a group of fat-soluble vitamin which can be obtained from a few foods, sunlight and supplements (Office of Dietary Supplements, 2009). The main role of Vitamin D is to assist the metabolism of Calcium and Phosphorus and also involve in mineralization of bone. Till now, different forms of Vitamin D have been discovered, they are named Vitamin D1, D2 , D3, D4 and D5 respectively.

They are prohormones. It means they are originally inactive, they have to undergo certain modifications to convert into active form. The figure below shows the two steps activation of Vitamin D prohormones (Figure 1). Two hydroxylation reactions for the Vitamin D prohormones for activation, the first hydroxylation takes place in the liver and intermediate called 25-hydroxyvitamin D (also called Calcidiol) are formed. The second hydroxylation takes place in the kidney and the intermediate 25-hydroxyvitamin D are then converted to active form known as 1,25-dihyroxyvitamin D (also called Calcitriol).

Figure 1: Pathway for the activation of Vitamin D

Source: Mana, B., 2008

They are secosteroids. It means they are steroids with one of the bonds in the rings broken. Steroid is a group of substances with a sterane core which consists of four rings (Figure 2). Vitamin D has the similar structure as steroid. However, some of the bonds in the rings of Vitamin D are broken (Figure 3).

Figure 2: Structure of Sterane

Source: Wikipedia, Steroid

Figure 3: Structure of Vitamin D2, D3, D4, D5

Source: Wikipedia, Vitamin D

There are two major forms of Vitamin D. They are Vitamin D2 and D3. The structure of Vitamin D2 and D3 are very similar, except the presence of a double bond between c22 and c23 and a methyl group in the C24 in the side chain of Vitamin D2 (Wikipedia Vitamin D).

Both Vitamin D2 and D3 are essential to Human. However, Vitamin D2 (also called ergocalciferol) cannot be produced by vertebrates included Human and should be obtained from external environment. They are believed to have a high efficiency to absorb UV radiation and protect the organisms (Holick, 2009)

Different from Vitamin D2, Vitamin D3 (also called cholecalciferol) can be made by UVB at wavelengths 270 – 300 nm (Wikipedia, Vitamin D). Furthermore, Vitamin D3 is more effective than Vitamin D2 in human since both duration and potency of Vitamin D3 are higher than that of Vitamin D2 (Laura et al.,2004). 

Source of Vitamin D

There are three ways to get Vitamin D such as sunlight, food and supplements and medications. Sunlight can help our skin to make Vitamin D from ultra-violet light (UVB rays). We can also through food to absorb Vitamin D like fatty fish, egg yolks and liver.

Source of Vitamin D – Sunlight

Sunlight is the best and only natural source of Vitamin D. When you get Vitamin D from sunshine, your body takes what it needs atomically and de-metabolizes any extra. Furthermore, 90 percent of our Vitamin D can naturally absorb from sunlight especially ultraviolet B exposure to our skin. It initiates the conversion of cholesterol in the skin to Vitamin D3. Sun exposure to the arms and legs for 10-15 minutes can produce thousands of units of Vitamin D which is 90% of our needed amount of Vitamin D. In addition, Full body exposure to sunlight is fortified with 3,000-20,000 IU (International Units) of Vitamin D (, n.d). However, the sun is not a reliable source for everyone as the season, time of day, geography, latitude, level of air pollution, skin color, and age all affect our skin’s ability to produce Vitamin D.

Limitation of Sunlight

UV-B can be called the “burning ray”. It is the primary cause of sunburn and is caused by overexposure to sunlight. But UV-B sunlight can produce Vitamin D on the skin. The amount of UV-B is not a constant. It is a variable and can be affected by a number of factors:

  • Latitude – The further north you are, the less there is
  • Altitude of location – The higher up you are, the more UV-B reaches you
  • Amount of skin surface exposed – The actual dosing of your sun expose is quite complex, since it involves knowing the amount of UV-B and one’s skin color
  • Skin pigmentation – The darker the pigmentation or more tanned your skin, the less UV-B penetrates. Window glass allows only 5 percent of the UV-B light range that produces Vitamin D to get into your home or auto
  • Season – Virtually less UV-B radiation in winter
  • Clouds – Can block UV-B
  • Pollution – Smog and ozone can block UV-B (Lee, 2008)

Alternative to UV exposure

Humans make and store abundant amounts of Vitamin D when skin is exposed to UVB from most indoor tanning equipment. E.g. tanning bed / sun bed. A single indoor tanning session (Maximum 20 mins) makes as much Vitamin D as 100 8-ounce glasses of whole milk (Uvsun, 2000). What’s more, UV exposure to tanning bed irradiation can increase pre-Vitamin D at a linear rate of 1 percent per minute. One week of exposure can lead to an increase in 25(OH) D by 50 percent, and five weeks of exposure can increase the level by 150 percent (Liu, 2008).

Source of Vitamin D – Food

Based on World’s healthiest Foods ranked as quality sources of Vitamin D, it indicated that salmon is excellent and also contains the highest nutrient density. Shrimp and milk are very good. Cod and egg are good too. Besides, some fortified and non-fortified food sources also contain Vitamin D such as cereal, orange juice, mackerel, sardines and tuna. Take orange juice and tuna as examples. If humans drink 8 oz of it, they can absorb 100 IU of Vitamin D. If humans eat 3.6 oz of canned tuna, they can absorb 300 IU of Vitamin D.

Join now!

Source: (2010) from

Source: Bordelon, P., Ghetu, M.V. & Langan, R. (2009).from

Importance of Vitamin D

Vitamin D plays an important role in maintaining our bone for lifelong health.  Also, it helps to maintain the level of calcium and phosphorus in human bodies.  Vitamin D works with estrogen in the kidney regulating renal tubular from reabsorption of calcium and phosphorus.  At the same time, Vitamin D works with PTH (parathyroid hormone) as to regulate the release of calcium and phosphorus from the bones into the bloodstream.  Figure 4 shows how Vitamin D is ...

This is a preview of the whole essay