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The Beginners Guide to Vitamins: Vitamin D

Often, we hear about vitamin deficiencies on our visit to the physician for being lethargic, uncomfortable sensations in muscles, muscle cramps, hair loss, and poor eyesight. So, what exactly are vitamins and why does our body need them? Vitamins are organic compounds required in small quantities for nutrition and normal growth, and our body cannot synthesize them. It is important to get them from food or in the form of supplements.

According to the National Health and Nutrition Examination Survey, approximately 41.6% people in the United States suffer from vitamin D deficiency. The digits may not sound fatal, but vitamin D deficiency is also associated with some chronic diseases. Let’s take a look at what is vitamin D, why you need it, and how much you should take it.

What Is Vitamin D?

Vitamin D is also called sunshine vitamin. We often think that it is the sun that is giving us vitamin D, but that is not true. We will resolve this myth as we go on.

Vitamin D is a fat-soluble (readily dissolved in fat unlike water-soluble) prohormone (a physiologically inactive precursor of a hormone) steroid. Due to its fat-soluble nature, it can be stored in the body for longer periods of time like vitamins A, E, and K.

Forms of Vitamin D

Vitamin D is found in two main forms, vitamins D3 and D2. Here, we are going to introduce some chemical names to make it easier to understand and differentiate.

  • Vitamin D3is also known as cholecalciferol.
  • Vitamin D2is also known as ergocalciferol.
  • Inactive form or precursor form is also known as7-dehydrocholesterol.
  • Biologically active form is also known as 1,25-dihydroxycholecalciferol or simply calcitriol.

Functions of Vitamin D in the Body

The main function of vitamin D is to act as a carrier for calcium. Vitamin D and calcium are closely linked because they work together. Vitamin D maintains the balance of calcium in your serum (a protein-rich liquid separated from blood after coagulation). Calcium and phosphates are two important minerals of our skeletal system.

Vitamin D controls the level of calcium in the bloodstream by two ways:

  • Taking calcium and phosphate from the intestine
  • Taking calcium from the bones

Hence working as a carrier, it has no direct effect on calcium concentration, but an optimal amount of Vitamin D is required to meet the flexible or continuously varying physiological needs of calcium.

Other important functions vitamin D performs depend on its need at the cellular level, i.e., for cell division, cell growth, and killing of unhealthy cells. That is why it performs its role of providing immunity (defense against disease) to your body and protection from cancer.

Vitamin D Deficiency

Vitamin D deficiency is a serious problem. It is often referred to as “rickets,” which is the deformation of bones in children. In adults, the deficiency is referred to as osteomalacia. Both rickets and osteomalacia reflect demineralization of newly formed bone matrix. It can be due to inadequate exposure to sunlight and decreased intake through diet.

However, there are various factors that influence the level of vitamin D. For instance, there are environmental factors like geographical area (latitude), season, weather, time of day, and amount of UVB radiation reaching the skin that affect vitamin D levels.

Personal variations also affect the production of vitamin D like:

  • Age – older people have thin skin, so it is hard to synthesize vitamin
  • Weight – obese people have less production
  • Clothing habits – less skin is exposed to sun

Sources of Vitamin D

There are three main sources of vitamin D

  • Sunlight
  • Dietary
  • Supplements


As we mentioned earlier, vitamin D is present in inactive form in the body. Then, how is it changed into its active form in the body? And how is the sunlight responsible for its activation? Well, let us tell you about an interesting phenomenon. Vitamin D goes through two steps to become useful from a useless state.

Vitamin D is present in its inactive form as 7-dehydrocholesterol in the skin and on exposure to sunlight, it can be converted into pre-vitamin D3and then to cholecalciferol. From skin (plasma membrane), it enters the systemic blood circulation.

Once in blood, cholecalciferol is converted into 25-hydroxycholecalciferol in the liver via the process of hydroxylation (the addition of -OH in the molecule). This form is also known as calcidiol. Calcidiol is not a biologically active form but requires further hydroxylation in the kidneys to be converted into 1,25-dihydroxycholecalciferol or calcitriol, which is the active and useful form.

A full-body exposure of 15 to 20 minutes of sunlight can produce up to 250µgof vitamin D, depending on the spectrum of light, geographical area, and wavelength of light.

Dietary Sources

Sunshine only provides vitamin D in the form of cholecalciferol (D3), while dietary sources can provide both ergocalciferol (D2) and cholecalciferol (D3). However, only a few natural resources can provide vitamin D. Vitamin D3can be obtained from animal sources like egg yolk, fish cod oil, salmon, tuna fish, beef liver, and cheese. Vitamin D2is usually obtained from plant sources like mushrooms.


Vitamin D is readily available as supplements to overcome the deficiency and avoid health problems. These supplements are inexpensive and available with or without calcium. Most multivitamins we take contain vitamin D2,but scientists are trying to produce multivitamins with D3as well.

For your convenience, here are some of the supplements you can easily find on Amazon:

Sports Research High Potency Vitamin D3with Coconut Oil

  • It delivers direct sunshine vitamin without being exposed to UVB rays in the sunlight.
  • It is gluten-free and non-GMO (Genetically Modified Organism).
  • Coconut oil is a nutritious fat and blends with vitamin D3to enhance its absorption.
  • Each capsule has 5000 IU (125 mcg) of high potency vitamin D3
  • Sports Research provides you money-back guarantee within 90 days of purchasing.

NatureWise Vitamin D35000 IU

  • It is a certified vitamin D3in olive oil which provides strength to muscles, bones, and teeth and supports the immune system.
  • It is non-GMO and gluten-free but contains gelatin.
  • It is available in the form of softgels which makes it more bioavailable (portion of drug actively available in the circulation) due to its liquid form. It also makes it easy to swallow.


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Written by Wayne Parker


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