Iron deficiency is the most common nutrient deficiency in the world. It’s especially important for women during their childbearing years to replace the iron lost each month through menstruation. And new studies show that being even mildly iron-deficient affects kids’ learning, memory and attention. Iron helps shuttle oxygen to your cells, which explains why iron deficiency can cause fatigue, fuzzy thinking and lowered immunity. Meat, poultry and seafood are top food sources of iron. Beans, greens and dried fruit are also rich in iron. Boost your iron intake by eating foods rich in iron together—a little meat can help you absorb more iron from beans and greens—or pair them with foods high in vitamin C.