"Vitamin D is a protein and is likely mostly digested when taken orally. Or not?"

 

 Vitamin D is actually **not a protein**, but a fat-soluble vitamin that plays a key role in calcium metabolism and bone health. There are two main forms of Vitamin D:

- **Vitamin D2 (Ergocalciferol)** – plant-based
- **Vitamin D3 (Cholecalciferol)** – animal-based or produced in the skin through sun exposure

### How is Vitamin D absorbed in the body?

When you take Vitamin D orally (through food or supplements), it is **not digested like proteins**. Since it is fat-soluble, it is absorbed in the small intestine along with fats from food. Here's an overview of the process:

1. **Absorption in the small intestine:**  
   Vitamin D is absorbed in the small intestine with the help of bile acids, which come from food or supplements. The presence of fat in food can improve this process.

2. **Transport into the bloodstream:**  
   After absorption, Vitamin D enters the lymphatic system and then the bloodstream, where it binds to specific transport proteins.

3. **Conversion in the liver and kidneys:**  
   In the liver, Vitamin D is converted into **25-hydroxyvitamin D (Calcidiol)**. This form is measured in the blood to determine Vitamin D levels. In the kidneys, it is further converted into the active form **1,25-dihydroxyvitamin D (Calcitriol)**, which has the actual effects in the body.

### Digestion of proteins and Vitamin D

Proteins are broken down into amino acids in the stomach and small intestine. Vitamin D, on the other hand, is a small, fat-soluble molecule and is not broken down into individual components like proteins. Instead, it is emulsified by bile acids and then absorbed.

### In summary:
- **Vitamin D is not a protein, but a fat-soluble vitamin.**
- It is not "digested" like proteins but absorbed in the small intestine along with fats.
- For optimal absorption, Vitamin D should be consumed with fat, as it helps the absorption process.