Why Do I Need Vitamin D? – The Sun – Hormone for Strong Bones

sun, ocean

Let the sun in. Today we are going to have a further look on probably one of the most important and versatile of the essential vitamins, which actually isn´t a vitamin at all. The talk is of vitamin D. And that is why we want to investigate the question “Why Do I Need Vitamin D? – The Sun – Hormone for Strong Bones”. We will learn, how much vitamin D we need, where we can get it from and what might happen if we are lacking this special vitamin.

Why is Vitamin D a hormone, which is good for the bones and what does the sun have to do with it?woman in the sun

Vitamin D or cholecalciferol is one of the few essential vitamins, which can be produced by our body by itself and it is the only essential vitamin, which can be produced with environmental influences within our skin. Then it actually works as a prohormone just before it is converted into its biologically active hormone form.

You may ask why vitamin D is good for our bones and what the sun has to do with it?

Vitamin D actively promotes the formation of bone substance. Predominantly this happens by the ability of vitamin D to integrate calcium into our bones.

The sun is the most significant source to supply our body with the precursors of the physiologically active form of vitamin D.

Out of the preform 7-Dehydrocholesterol, which is a form of cholesterol, in addition to ultraviolet sunlight in the area of 290–315 nm forms an unstable pre-vitamin, which is converted into the prohormone vitamin D3.

So now you know that vitamin D(3) actually is a prohormone, which will be converted into a hormone, on which we have a look later. You also know that this hormone promotes the formation of bone substance by helping to integrate calcium into them. And the sunlight is the biggest source to form the prohormone vitamin D(3).

Let us dive deeper now.


What is Vitamin D?

Vitamin D is a vitamin, which is fat-soluble and is actually acting as a prohormone in our body, which is converted into the hormone calcitriol. It is essential and can be produced by the body on its own when the skin is exposed to intensive sunlight. There are two important bioactive forms of vitamin D, which are vitamin D3 or cholecalciferol (found in animal food) and vitamin D2 or ergocalciferol (found in plant food). Vitamin D3 has the highest bioactivity within our body. If we are speaking of vitamin D, we usually mean vitamin D3 or D2. Vitamin D is by the old definition not a vitamin because our body can produce it with the help of the sun on its own. The old definition only includes vitamins, which are only accessible through nutrition. But as it is strictly essential for our body, it found its way into the list of the essential vitamins.


What is the demand of Vitamin D?

Depending on the age, health and lifestyle the daily demand for an average and healthy adult for the essential vitamin D is 20 (μg) per day. A very commonly used unit for vitamin D is the unit “International Units”. The conversion of μg into IU is 1 μg = 0,001 mg ≡ 40 IU. That means that we have to get 800 IU per day.


Where can you get Vitamin D from (Top foods)?

Here are the Top foods, which are rich in vitamin D:

sun at oceansalmon

1. Equatorial Sunlight (up to 10.000 – 20.000 IU/day)*


2. Fat fish like salmon (up to 1.000 IU/100g)


3. Meat like beef (up to 150 IU/100g)



cow4. Avocado (up to 137 IU/100g)


* The brighter the skin is, the less time it takes to achieve the needed sunlight dose. It is dependent on the amount of melanin, a skin pigment, which also protects us from vitamin D intoxication. The time interval begins from about 10 minutes for a very low amount of melanin, until about 120 min for a very high amount of melanin.


What are the functions and benefits of Vitamin D?

We have learned above, that vitamin D works as a prohormone and has many different, important functions in our body. Now we will have a closer look at this functions.

(Pro)hormone, which is the precursor of the biologically active hormone calcitriol

Calcitriol is the biologically active form of vitamin D, which takes effect in many processes in our body, which we will discuss next. The conversion-chain from cholesterol, which comes from the liver, to calcitriol, which is active in the cells, has several intermediate stages. The most important intermediate form is cholecalciferol (vitamin D3), which is then converted after its transport back to the liver into calcidiol, which is the transport form of vitamin D in our blood. As calcidiol arrives at its destination at the cell, it is converted into calcitriol, which can interfere within the metabolism on the cellular level by docking at the designated receptors.

Regulation of the integration of calcium in our bones

Probably the best known and very important function of vitamin D is its ability to integrate calcium into our bones. This can happen because vitamin D supports the absorption of calcium and phosphate in our gut. For this, vitamin D is responsible to produce calcium-transporting-proteins, which let calcium arrive from the gut to the bones. For the activation of this transport-proteins vitamin K2 is necessary. We will have a closer look at this essential vitamin in a blog post soon.

As vitamin D has a regulating function within the calcium-cycle, it also has the ability to reabsorb calcium from the blood, so that it can be excreted through the urine.

So now we know why missing vitamin D can promote osteoporosis, although we may have enough calcium at place. The calcium cannot be transported as vitamin D is missing to transport it.

Genetic modulator, effect on the DNA and in the protein metabolism

Nearly every cell in our body has a vitamin D receptor. Is vitamin D docking on one of these receptors, proteins and specialized enzymes as well as neurotransmitters like serotonin can be built. Within this protein-metabolism vitamin D is able to have an influence on more than 2000 genes.

Immune modulator

Vitamin D has several functions concerning our immune system. It ensures the formation of immune defense cells. Moreover, it is regulating immune responses, so that inflammatory processes within inflammations or auto-immune reactions are limited.

Effect in the nerve system

Vitamin D regulates the cycle of the formation of nerve cells in the whole nerve system in our body. It protects all the nerve cells, including the cells in the brain. And it is able to promote the synthesis of several neurotransmitters.

Cell formation, cell division

Especially for the fast-dividing body cells like skin and hair cells, vitamin D seems to play a significant role. But there is still research to be done.


What deficiency symptoms of Vitamin D exist?

A hypovitaminosis of vitamin D is very common in big parts of the population in the northern (north of the 42th latitude) and southern (south of the 42th degree of latitude) hemisphere. Potential factors for a deficiency in vitamin D are a lack of disposition to sunlight, which is the most common source for a deficiency and overweight. One of the well-known diseases, caused by a lack of vitamin D is rickets occurring for children leading to deformation of the bones. For adults, this deficiency disease is called osteomalacia. Typical symptoms of a lack of vitamin D can be as followed:

  • weakness
  • weak immune system
  • tiredness
  • lack of concentration
  • (winter) depression
  • rickets
  • rachitis/osteomalacia
  • osteoporosis
  • cardiovascular diseases
  • cancer
  • dementia
  • diabetes


What overdose symptoms of Vitamin D exist?

A hypervitaminosis of vitamin D is possible as well through supplementation, beginning lightly at more than 10.000 IU/day with short time symptoms like gastrointestinal problems, thirst, weakness and a headache. At higher doses of more than 40.000 IU/day, the potential risk for arteriosclerosis rises as a long time result, together with kidney stones and mineral deficiencies.


What else may you have to consider about Vitamin D? 

Value in our body

The highest concentration of vitamin D3 can be found in the upper skin or epidermis. Vitamin D3 can be stored in the liver for about 29 days.


Antagonists and Advice

The skin pigment melanin works as a natural limiter for the formation of vitamin D3. The more melanin is at present, the less vitamin D3 is built.

For people, who are living in the temperate climate zones and with a comparatively low amount of melanin a sunbath of about 20 minutes three times a week in the summer months or the warmest months is necessary to maintain a solid vitamin D level. In the winter months or the coldest months it is not possible to maintain a solid level of vitamin D. So it is recommended to take a vitamin D supplementation (vitamin D3 with vitamin K2) throughout winter unless you are not a big eater of fish and meat. That on the other hand leads to other disadvantages such as heavy metal intoxication or a higher risk for gout.

A big antagonist for the formation of vitamin D in our skin is suncream, which blocks the ultraviolet sunlight and makes it impossible to built high doses of vitamin D. So first without suncream into the sun. And if you are staying longer in the sun, then protect your body with clothes or use suncream on remaining exposed skin areas if necessary.

As a reader mentioned in a comment, there are research results, which propose, that a shower with soap can reduce the formation of vitamin D because much of it will be washed away. So give your skin some hours (4-6) to built vitamin D and then use the shower.

Discovery and Use

Vitamin D was discovered in 1919 in cod liver oil.


The word calciferol comes from the word creation calcif(erous) + (ergost)erol. Ergosterol is a precursor of vitamin D2, which is present in plants.



Wow, vitamin D truly is an awesome vitamin for us. And rightly vitamin D deserves to get in the same prominent position as vitamin C is now. Let´s recapitulate why that is so.

For long times vitamin D was known to prevent us from bone deformation called rickets or osteomalacia and even osteoporosis. And that is because vitamin D plays an important role within the calcium cycle in our body. It enables the transport from the gut to the bones.

Moreover, vitamin D participates within the formation and the protection of body cells like skin and hair cells and all nerve cells and is especially important for the formation of brain cells. It is also indispensable for our protein metabolism and ensures a good function of our immune system by promoting the formation of immune defense cells and by regulation inflammatory processes.

The sun is the most important source for our vitamin D level. Besides fat fish, meat and some plants like avocados can increase our vitamin D value a bit.

Let us know what you think about this topic? Was this blog post helpful for you? What else do you know or want to know about vitamin D? Please leave your comment below.

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