As you breathe, you take in oxygen from the air that is required by every cell in your body. How does this oxygen know to go where it's needed? Thank iron for that! The iron in hemoglobin delivers oxygen from the lungs to other body tissues. Without it, anemia - caused by iron-deficiency, which affects 240,000 toddlers and 3.3 million women in the United States - can lead to fatigue, impaired concentration, and compromised immune function.