What role does the skin play in proper calcium absorption from the digestive tract?

The UV light from the sun initiates a chemical reaction in our skin. This reaction produces vitamin D3 (also known as cholecalciferol) from 7- dehydrocholesterol.

About 20% vitamin D comes from the dietary source. But the vast majority (80%) is produced in the skin.

Vitamin D3 produced in the skin is hydroxylated two times (first in the liver then in the kidney) and produce 1,25-Dihydroxyvitamin D3 (1,25 Dihydroxycholecalciferol). This is the active form of vitamin D.

The activated vitamin D has the following functions :
Among these functions, calcium homeostasis is an important one. Active vitamin D increases the absorption of calcium and phosphate from the intestine, thus maintaining the homeostasis of calcium.

So, skin plays an important role in proper absorption of calcium from the intestine, by producing vitamin D.