Iron is the most common nutritional deficiency worldwide, affecting ~2 billion people. It is essential for oxygen transport and energy metabolism.

Functions:

• Component of hemoglobin — carries oxygen in red blood cells
• Component of myoglobin — stores oxygen in muscle
• Required for energy production (mitochondrial enzymes)
• Immune function and DNA synthesis

Two forms of dietary iron:

• Heme iron — from animal foods (meat, poultry, fish). 15–35% absorption rate.
• Non-heme iron — from plant foods (legumes, spinach, fortified foods). 2–20% absorption rate.

Enhancing absorption: Vitamin C dramatically increases non-heme iron absorption. Eat together.

Inhibitors: Calcium, tannins (tea/coffee), phytates (whole grains) reduce iron absorption.

Iron deficiency anemia symptoms: Fatigue, weakness, pale skin, brittle nails, shortness of breath.

Reference:

Wikipedia: Iron deficiency

https://en.wikipedia.org/wiki/Iron_deficiency