What is and how do we use vitamin D

Vitamin D is a group of secoesteroids soluble in fat which a lot of biological effects. The two main forms of vitamin D are vitamin D₃ or cholecalciferol and vitamin D₂ or ergocalciferol.

Vitamin D is the only vitamin we can synthesize by ourselves, which technically makes it not a vitamin. To synthesise it we need the sunlight’s help, when the skin is exposed to the UVB rays it produces vitamin D₃ from the molecule 7-dehydrocholesterol which you can guess by its name comes from cholesterol. Cholesterol has a undeserved bad reputation, cholesterol plays a big role in our health, it's really sad that general population think it's something bad, because as you can see it participates in a lot of reactions that keep us alive.

The amount of vitamin D produced through sun exposure depends on the age, season of the year, moment of the day, latitude, skin tone (the darker it is the less vitamin D it produced), sunscreen use and how much clothes the person is wearing.

Are vitamin D₂ and D₃ the same?

Vitamin D₂ comes from plants and D₃ from animals. Some studies say that both forms of vitamin D are the same, meaning both should be as effective when doing their job, while other studies say that vitamin D₃ is much better. The problem is that on top of that lack of consensus, many authors work for supplement companies, so you can't trust their opinion. That's why I prefer to rely on vitamin D₃ just because of the odds. If I rely my diet on consuming vitamin D₃ rich product, I'm getting sure it works just fine, I have a 100% chance of not being wrong. Instead, with vitamin D₂, there's a 50% chance of choosing the source of vitamin D that's not as efficient as it should be.

Vitamin D functions

Calcium homeostasis

The main function of vitamin D is to manage calcium homeostasis (the body's equilibrium state). To do this the vitamin D molecule has to suffer some changes. Either if it comes from the diet or from the exposure to sun, vitamin D goes to the liver to be transformed into 25-hydroxyvitamin D, which is the form doctors measure vitamin D levels in the blood. Then it goes to the kidneys to be transformed into the activated form called 1,25-dihydroxyvitamin D. This molecule goes to the intestines, where the cells from the intestinal wall have vitamin D sensitive receptors. Imagine a receptor as a lock, the 1,25-dihydroxyvitamin D receptor can only be activated by this molecule and not any other. Once this receptor is activated the calcium absorption is increased.

On the other hand, if the body needs calcium, then 1,25-dihydroxyvitamin D goes to the bones where it activates a process to remove calcium from the bones and send it to the bloodstream. This maintains a stable calcium level in the blood all the time. If a person doesn't eat an appropriate amount of calcium, bones get demineralized and if this happens during the growth of a child, it can have severe effect like malformations.

Other functions

Vitamin D also affects the functioning of the immune system, for 25 years it has been recognized the role it plays in it, but in the last few years more attention has been drawn to how it exactly does this.

This is not easy to explain, so I'll talk about it in a future post. But to give you an idea of what vitamin D does I'll give you some examples:

• Regulates the lymphocytes T function which are one of the immune system's response against a danger.
• Down-regulates some inflammatory markers like interleukin-2 or 12. Remember inflammation is one the responses of the immune system.
• Suppresses malign cell growth (tumors).

Deficiencies

According to the World Health Organization (WHO), vitamin D deficiency is a world health problem, which is more frequent in places where sun exposure is limited. Elder and dark skin people are at higher risk for vitamin D deficiencies, since their skin produces less of it when exposed to sun.

There are also rare genetic defects that can affect the vitamin D metabolism, so no matter how much sun exposure they have or how much vitamin D they ingest they will not use it.

Vitamin D deficiency is defined as a level lower than 20 ng/mL of 25 hydroxyvitamin D in the blood. Lower levels than that rise the risk of suffering chronic diseases including autoimmune ones like type 1 diabetes, multiple sclerosis, rheumatoid arthritis, deadly cancers like the prostate, colon or breast, cardiovascular diseases and stroke and even deformities in children like rickets. Another problem that's pretty common and people don't associate it with vitamin D deficiency is depression. Believe it or not, some depressions are not caused by our problems, but by our diet.

It also exists the insufficiency of vitamin D which goes from 21 to 29 ng/mL of 25 hydroxyvitamin D, meaning it can handle its basic tasks but it's not optimal, humans can thrive on these levels. What's optimal for children development and proper health is above 30 ng/mL of 25 hydroxyvitamin D.

Supplements

I'm not a fan of supplements, I think that a diet rich in animal products should give you what you need in a balanced way. Taking supplements can be dangerous. To have an overdose through diet you would need to eat a ridiculous and impossible amount if fish, to do the same with supplements you just have to take the wrong amount of it. The problem with supplements lies on the fact that vitamins and minerals sometimes don't work isolated, many times they need another vitamin or mineral to carry out its job. For example, a well-known pair in biochemistry is sodium and potassium and others not so known are calcium and magnesium or vitamin D with vitamin K.

Vitamin K also affect the calcium homeostasis since it activates some molecules like the matrix Gla protein or the osteocalcin which bond to calcium in the blood to inhibit the formation of salts inside the veins. There are evidence that an excess of vitamin D could increase the calcium levels in the bloodstream, if there's not enough vitamin K to remove it and take it away to somewhere else it could increase the risk to suffer cardiovascular diseases.

Sources

The best source is sun exposure, there's no food that can give you the same amount of vitamin D. Ideally you should get enough sun exposure during summer (without sunscreen) to fill the vitamin D storage. This doesn't mean to be all day without sunscreen exposed to the sun, that's dangerous. Since vitamin D is soluble in fat it is stored in the fatty tissue this way, we can access to it during winter when the sun is scarce.

If you can't get sun exposure, because of your job or whatever then you need to eat more foods high in vitamin D. The following foods have a good amount of vitamin D, the data is per 100 grams (2):

Only D3

• Wild caught salmon ∼600–1,000 IU
• Canned sardines ∼300 IU
• Canned Mackerel ∼250 IU
• Fresh Mackerel 403 IU
• Canned tuna 236 IU

Only D2

• Fresh shiitake mushrooms ∼100 IU
• Dried shiitake mushrooms ∼1,600 IU

Combination D2 y D3

• Fresh farmed salmon ∼100–250 IU
• 1 Egg yolk ∼20 IU
• Leche 40 IU

Conclusions

As you can see vitamin D's job is super interesting and essential for our health. Some of the nowadays elderly have bone problems, probably because they lived in rough times, where food was scarce. We are lucky to live in a world plenty of resources, use them wisely.

Remember to get enough sun exposure during summer to fill that vitamin D tank and eat fish during winter.

I hope this was interesting and helpful.

Until next time, bye!

References

1. Lips, P. (2006). Vitamin D physiology. Progress in Biophysics and Molecular Biology, 92(1), 4–8. doi: 10.1016/j.pbiomolbio.2006.02.016
2. Michael F. Holick. Vitamin D and Health: Evolution, Biologic Functions, and Recommended Dietary Intakes for Vitamin D. M.F. Holick. Springer Science+Business Media, LLC 2010. doi: 10.1007/978-1-60327-303-9_1
3. Adriana J. van Ballegooijen, Stefan Pilz, Andreas Tomaschitz, Martin R. Grübler, and Nicolas Verheyen6. The Synergistic Interplay between Vitamins D and K for Bone and Cardiovascular Health: A Narrative Review. International Journal of Endocrinology. Volume 2017, Article ID 7454376, 12 pages. doi: 10.1155/2017/7454376
4. Martin Hewison. Vitamin D and immune function: an overview. Proceedings of the Nutrition Society (2012), 71, 50–61. doi: 10.1017/S0029665111001650