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Vitamin D is a hormone

All You Need to Know about Vitamin D

Published 1 year ago at 12 Jan 2021 by Alexandra Soare

Vitamin D is a fat-soluble vitamin that includes D1, D2, and D3 components. Your body can produce it when your skin is exposed to the UVB radiation from the sun. Since vitamins cannot be synthesized by the body, technically this molecule is a hormone.

Why is it important?

The main role of this vitamin is to help calcium and phosphate absorption. This allows us to build and maintain strong bones. The first to take advantage of it were the vertebrates. They ate plankton (rich in Vit. D) in order to better absorb the calcium present in the ocean.

This vitamin helped eradicate rickets. Scientists realized that dogs kept in underground cages developed weak bones. Also, military personnel who spent a long time in submarines, had similar issues. Supplementing it, has saved a lot of lives. Later on, it was discovered that this vitamin also has the following properties:

Vitamin D benefits:

  • beautiful teeth, strong muscles and bones because of calcium absorption and retention. Without it, the calcium would be eliminated through the kidneys.
  • support for the immune system and the nervous system by stimulating the antibacterial, antiviral and anti-inflammatory effects.
  • reduction of depression and anxiety because of the action of Vit. D receptors in the brain cells that regulate adrenaline, noradrenaline and dopamine production in the brain; as well as protecting serotonin from being destroyed.
  • weight loss contributor (might act as an appetite-suppressant) and insulin regulator.

Certain studies found a likelihood in reducing the risk of heart disease, cancer, multiple sclerosis or flu. However, it is not clear whether it is due to the Vitamin D influence or because people with higher levels of Vitamin D generally spend more time outdoors and are more active (which could play a role).

How much do you need?

You can find the vitamin D measurements in micrograms (written with the Greek symbol μg) or International Units (IU). Find out how much Vitamin D you need by asking your doctor for a blood serum test.

  Vitamin D status Serum levels of 25‐OH‐D (ng/mL)
Deficiency <20
Insufficiency 20–29
Sufficiency ≥30

How much vitamin D do you need in order to reach a sufficient amount? It is not clear, that's why many scientific studies and organization will suggest different numbers. The WHO (World Health Organization) suggests 600 IU per day for an adult with no medical complications with a limit of 4,000 IU. Because Vitamin D is produced when the skin gets stimulated by the UVB rays, it is not easy to measure the produced amount.

Should you supplement D2 and D3?

D2, also known as ergocalciferol, is synthesized in fungi and plants (that's why mushrooms contain it).
D3, known as cholecalciferol, is produced by animals and humans. It is the preferred component for the human body. It is more efficient because it is sustained in the blood for longer.

Why are your Vitamin D levels low?

The main reason why you might have low Vitamin D levels has to do with sun exposure. Especially between October and early March, because of the Earth's inclination, we don’t get enough UVB radiations from sunlight. 

  • spending too little time outdoors
  • living in industrialized cities/areas with high pollution
  • using too much sunscreen
  • skin type absorption (for more, check down below)

Symptoms of a Vitamin D deficiency:

  • tiredness, overall feeling bad/not like yourself
  • muscle and bone pain
  • getting sick often
  • low mood/depression
  • hair loss

Special cases for Vitamin D deficiency:

  • if you suffer from colitis, Crohn's or celiac disease: the intestine has difficulty absorbing Vitamin D.
  • weightloss surgeries: reduction of the small intestine = where the vitamins are absorbed
  • obesity. Because Vitamin D is a vitamin stored in fat, fat cells can accumulate t making it less available
  • kidneys and liver disease: reducted quantity of a special enzyme that is needed to transform vitamin D.

3 main sources for Vitamin D3

The best sources of Vitamin D are sunlight, food and supplements. The safest and most efficient one is the sunlight. When you reached an adequate level, the skin automatically blocks the production of pre-vitamin D. This protects the body from hypercalcämia. The same cannot be said for oral supplementation. Check with a professional, as supplements may interfere with current medications or health conditions.

1. Sunlight

A special type of cholesterol, when exposed to ultraviolet B, reacts to this particular wavelength of 290–315 nm. Here the 7-Dehydrocholesterol is transformed into Previtamin D.

UVA = potential risk for cancer under certain limits
UVB = production of Vitamin D3
UVC = stopped by the OZON layer

The amount of ultraviolet B rays that can reach your skin depends on Earth's inclination. 

Impact of UVA, UVB and UVC on Earth surface
How much time should you spend in the sun?
Depends on the time of the day, where you live, the season, your skin type and the amount of skin exposed.

The ideal condition would be:

Time of the day: between 11 and 3 pm, in a season: between April and September, living near the Equator, skin type 1. In this case, you would need only 10 mins of exposure. If your situation is different you might need around 20min of exposure a day. In certain cities (polluted and with little UV light level) you might need to supplement.

2. Food sources

Unfortunately, Vitamin D is not present in high enough amounts to cover your daily needs. You can find it present naturally in small amounts in:

  • cod liver
  • oily fish – such as salmon, sardines, shrimps, herring, tuna fish and mackerel
  • red meat
  • beef liver
  • egg yolk
  • mushrooms

Fortified foods (Vit. D can only be added in small amounts)

  • breakfast cereals
  • eggs
  • milk
  • yogurt
  • orange juice
  • infant formula (added by law)

3. Supplements

When should you take supplements?

  • if you are not often outdoors
  • age (after a certain age, the skin has less and less power to absorb vitamin D)
  • work nightshift
  • are in an institution like a care home
  • usually wear clothes that cover up most of your skin when outdoors
  • If you have dark skin – for example you have an African, African-Caribbean or south Asian background – you may also not get enough vitamin D from sunlight. That's because a darker skin tone absorbs less ultraviolet radiation B (UVB)
    The melanin acts like a protection against UV radiation (more protected against skin cancer but also absorb less vitamin D)

List of skin type and impact on UV rays

What is the best supplement?

The ideal supplement needs to have the following three characteristics:

  • vitamin D3 (instead of Vitamin D2) is better absorbed and retained in the blood
  • combined with vitamin K2 and Magnesium for maximum efficiency
  • in gel or liquid because it is a fat-soluble vitamin and it has to be taken with a fat-carrier
  • high-quality production. Keep in mind that not all brands are optimal. For example, some gummies are just sprayed with a vitamin D solution, instead of having a proper supplementation process.

Can you overdose?

Yes, there have been some rare cases of overdose. Taking too much vitamin D can harden your blood vessels and tissues due to increased levels of calcium in your blood. This will over time weaken also your heart and kidneys.

How much Vitamin D is too much?

The WHO (World Health Organization) suggests a limit of 4,000 IU per day for an adult. However many scientific studies prove that a vitamin D toxicity is unlikely at intakes under 10,000 IU per day.

Symptoms when you consume too much:

  • headache
  • nausea and vomiting
  • poor appetite
  • dry mouth/feeling of thirst
  • a metallic taste

Good news: You cannot overdose on vitamin D through exposure to sunlight. UV rays end up photo‐degrading vitamin D after a certain period of time.

Bonus facts about Vitamin D3

Did you know you cannot absorb UVB rays through windows? The glass blocks the UVB radiations, it only allows the UVA to pass. If you are planning on having a sunbath indoors, unfortunately, it won't be effective.

Do tanning devices, boots or UV-lamps work? This is a great question! Logically it would make sense to use this artificial light, but the UVA production is so high that in many countries they are not allowed to operate because of the dangerous risk for cancer. Just to make a comparison on the unbalanced ratio:

  • Tanning devices have a higher UVA emission compared to the index of a summer day at noon in Italy.
  • UVB power instead is very low, compared to the one of summer light in Oslo. Not only it is not worth it, but it also exposes you to the dangerous UVA rays.

Is there a solution? Yes! In commerce, there are some medical devices that emit only UVB rays. They are safe and efficient to use.


Vitamin D3 is extremely important for your health. If you live in a country with little sunlight in winter or if you don't have the chance to spend time outdoors, I highly recommend you check your Vitamin D serum levels. If your doctor notices a deficiency, follow his advice and supplement or use a medical band device.

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