Vitamin D Supplementation

Vitamin D, often called the “sunshine hormone,” plays a vital role in overall health. Many people in the Western world are deficient in it, but before deciding to supplement, it’s essential to test your blood levels (Calcifediol). This can help you understand whether supplementation is necessary and how much you need to reach optimal levels.

Key considerations include your current blood levels, lifestyle, UVB exposure, skin tone, BMI, and health conditions. Vitamin D3 (Cholecalciferol) is the preferred supplement form, as it is more effective than Vitamin D2. Individuals with higher BMIs or certain health conditions may require higher doses or specialized forms like Calcifediol or Calcitriol.

Vitamin D

Calciol Production

Cholecalciferol Production

When exposed to sunlight, your skin produces [vitamin D](https://www.allmer.de/blog/vitamins/vitamin-d/vitamin-d/). How much you create depends on your skin type, time in the sun, and how much skin is exposed. We can estimate this using two simple steps. First, we calculate how much [vitamin D](https://www.allmer.de/blog/vitamins/vitamin-d/vitamin-d/) your skin makes per square centimeter per minute based on UV radiation and daylight hours. Then, we adjust that number for how long you’re outside, how much skin is exposed (like arms, legs, and face), and your skin type. For example, exposing 5,000 $cm^{2}$ of skin to the sun for 30 minutes will produce more [vitamin D](https://www.allmer.de/blog/vitamins/vitamin-d/vitamin-d/) if done around noon when UV rays are strongest. Always avoid sunburn!

For more technical details, read on.

When our skin is exposed to UVB rays, e.g., during sun exposure, Cholecalciferol aka Calciol is produced from 7-Dehydrocholesterol. In a 1977 publication, PC Beadle estimated that about 160 IU Cholecalciferol could be produced at 40° Latitude when exposing 1 $cm^{2}$ of skin to the sun for the whole day. Dark skin would produce around 70 IU under the same conditions. This information is suboptimal to drive the decision of how to expose oneself to the sun.

Vitamin D

Everything about Vitamin D — from production and regulation to supplementation and testing.

Vitamin D

Calciol

Cholecalciferol

[Vitamin D](https://www.allmer.de/blog/vitamins/vitamin-d/vitamin-d/), also known as cholecalciferol (aka Calciol), is a hormone that our skin makes when exposed to sunlight, specifically UVB rays. For this to happen, we need enough of a molecule called 7-dehydrocholesterol in our skin. If we don't get enough sunlight, whether it's because we stay indoors, wear too much clothing, or use sunscreen, we can't produce enough vitamin D. When vitamin D enters our blood, it can either float freely or bind to a protein called DBP. Once in the bloodstream, vitamin D can be taken up by fat and muscle cells for storage. Our body can also convert vitamin D into different forms, like calcifediol and calcitriol, which are more active in the body. The names of these forms refer to the number of hydroxyl groups (OH) added to the molecule—one for vitamin D, two for calcifediol, and three for calcitriol. Studies measuring vitamin D levels in people have shown differences over time. For example, a 1984 study found lower levels in healthy subjects (around 3-5 ng/ml), while a 2013 study reported higher levels (around 37-45 ng/ml). These variations might be due to changes in vitamin D supplementation or other factors. However, these levels don’t necessarily have clear biological or medical significance.

For more technical details, read on.

Vitamin D

Vitamin D, technically a hormone, is made in the skin when UVB rays convert a cholesterol compound into D3 (Cholecalciferol, or Calciol). Many people don’t make enough due to lack of sun exposure, so we rely on food (like fatty fish) or supplements. Plants provide D2 (Ergocalciferol), but D3 works better in our bodies.

D3 has three key forms:

Calciol: Stored in fat for long-term use; this is the form we produce or ingest.
Calcifediol: Formed in the liver for short-term storage, circulating in blood and commonly tested to check D3 levels.
Calcitriol: The active form, made in the kidneys, with a short lifespan but crucial for biological effects.

We’ll be using the terms Calciol → Calcifediol → Calcitriol throughout future discussions.