Which hormone is primarily responsible for increasing calcium absorption in the gut?

• A. Calcitonin
• B. Parathyroid hormone
• C. Vitamin D
• D. Thyroxine

Answer: (C)

Vitamin D is primarily responsible for increasing calcium absorption in the gut. It is a fat-soluble vitamin that facilitates the intestinal absorption of calcium and phosphate, which are vital for maintaining healthy bones and teeth. When calcium levels in the blood are low, the production of active Vitamin D (calcitriol) increases, leading to enhanced absorption of dietary calcium in the intestines, thus helping to maintain adequate serum calcium levels.

While parathyroid hormone also plays a crucial role in regulating calcium levels, its primary function is to increase calcium levels in the bloodstream by acting on the bones, kidneys, and indirectly through Vitamin D, rather than directly enhancing intestinal absorption. Calcitonin, on the other hand, generally functions to lower blood calcium levels by inhibiting bone resorption. Thyroxine is involved in metabolism and development but does not have a significant impact on calcium absorption in the gut. Understanding these distinct roles highlights why Vitamin D is the cornerstone hormone for increasing calcium absorption in the digestive system.