Where are iron and calcium mainly absorbed in the small intestine?

In the human digestive system, both iron and calcium are primarily absorbed in the duodenum, which is the first and shortest segment of the small intestine.123

• Calcium: Absorption occurs primarily in the duodenum, where stomach acid helps convert calcium into a salt form that can be absorbed across the brush border of the enterocyte cell membrane. This active transport process requires energy and is dependent on Vitamin D.1
• Iron: Iron is almost entirely absorbed in the duodenum through a metabolic process that requires energy. Once absorbed, it is transported from the enterocyte by binding to a plasma protein called transferrin.3

While the jejunum is the primary site for the absorption of many other nutrients, the duodenal mucosa is specifically noted for initiating the absorption of these essential minerals before food contents move further into the digestive tract.42