What is the Difference Between Cholecalciferol and Calcitriol

The main difference between cholecalciferol and calcitriol is that cholecalciferol is a type of vitamin D that is made by the skin when exposed to sunlight whereas calcitriol is the active form of vitamin D that occurs in the kidney.

Cholecalciferol and calcitriol are two forms of vitamin D with different functions. Vitamin D is a micronutrient that increases the intestinal absorption of calcium, magnesium, phosphate, and many other biological effects. Moreover, vitamin D is a fat-soluble vitamin.

Key Areas Covered

1. What is Cholecalciferol
   • Definition, Features, Importance
2. What is Calcitriol
   • Definition, Features, Importance
3. Similarities Between Cholecalciferol and Calcitriol
   • Outline of Common Features
4. Difference Between Cholecalciferol and Calcitriol
   • Comparison of Key Differences

Key Terms

Calcitriol, Cholecalciferol, Vitamin D

What is Cholecalciferol

Cholecalciferol or vitamin D3 is a type of vitamin D. Usually, it is made by the skin upon exposure to sunlight. It also occurs in food and is important as a dietary supplement. Normally, some fish, beef liver, eggs, cheese, cow milk, fruit juice, yogurt, and margarine contain vitamin D3. In the liver, cholecalciferol converts into calcifediol (25-hydroxyvitamin D), which then converts into calcitriol in the kidney. However, the vitamin D taken either from sun exposure or from the diet is biologically inactive. This inactive vitamin D has to undergo two hydroxylation steps in order to become active. The first hydroxylation of cholecalciferol occurs in the liver. The hydroxylation of calcifediol into calcitriol in the kidney makes the active form of vitamin D. This active form of vitamin D is calcitriol.

Figure 1: Cholecalciferol

Furthermore, the main function of vitamin D is to help in calcium homeostasis and metabolism. In addition, the deficiency of vitamin D3 can cause rickets in children.

What is Calcitriol

Calcitriol or 1,25-dihydroxycholecalciferol is an active form of vitamin D produced in the kidney. Calcitriol is a hormone that activates the vitamin D receptor in the nucleus of the cell. It also increases the expression of many genes. At the same time, calcitriol increases the blood calcium level by increasing the uptake of calcium from the intestine.

Figure 2: Calcitriol

Moreover, calcitriol is a medication for low blood calcium and hyperparathyroidism due to kidney disease. In addition, calcitriol increases the renal tubular reabsorption of calcium and stimulates the release of calcium from bones. More importantly, the main function of calcitriol is to increase the blood calcium level.

Similarities Between Cholecalciferol and Calcitriol

• Cholecalciferol and calcitriol are two forms of vitamin D.
• The main function of vitamin D is to increase blood calcium levels.

Difference Between Cholecalciferol and Calcitriol

Definition

Cholecalciferol refers to one of the D vitamins, a sterol essential for the deposition of calcium in bones and formed by the action of sunlight on dehydrocholesterol in the skin, while calcitriol refers to the active form of vitamin D, normally made in the kidney.

Occurrence

Usually, the skin produces cholecalciferol while the kidney produces calcitriol.

Significance

Cholecalciferol is vitamin D3 while calcitriol is the active form of vitamin D.

Function

The function of cholecalciferol is to convert into calcifediol in the liver while the function of calcitriol is to act as a hormone that increases the blood calcium level.

Deficiency

Vitamin D deficiency can cause rickets in children while calcitriol deficiency can cause hypocalcaemia. 

Conclusion

In brief, cholecalciferol and calcitriol are two forms of vitamin D. Cholecalciferol is vitamin D3 while calcitriol is the active form of vitamin D. While epithelial cells of the skin produce cholecalciferol upon exposure to sunlight, the kidney produces calcitriol from calcifediol. In addition, calcitriol serves as a hormone that increases blood calcium levels in different ways: promoting absorption of calcium from the gastrointestinal tract, increasing the renal tubular reabsorption of calcium in the kidney, and stimulating the release of calcium from bones. The main difference between cholecalciferol and calcitriol is their action.   

References:

1. Wikimedia Foundation. (2022, August 23). Vitamin D. Wikipedia. Retrieved August 23, 2022.

Image Courtesy:

1. “Cholecalciferol2 ” By NEUROtiker – Own Work (Public Domain) via Commons Wikimedia
2. “Calcitriol ” By Ayacop – Own Work (Public Domain) via Commons Wikimedia