Hemoglobin, which is the protein within red blood cells that transports oxygen, requires iron to develop and function. Without an ample supply of oxygen, our body's cells become impaired within moments and no longer have the energy to carry out the vital processes of life. Iron also helps to support amino acid metabolism and synthesis, all of which help support muscle and cognitive function. A deficiency in iron might possibly cause symptoms such as fatigue, weakness, shortness of breath, headaches, dizziness and lightheadedness. Iron deficiency is one of the most common nutrient deficiencies worldwide. It most often affects pregnant women, infants and young children, women with heavy menstrual bleeding, and frequent blood donors. Although iron is abundant in red meat, beans, and dark green leafy vegetables, significant parts of the population do not consume enough of these foods to prevent deficiency. This is especially true for vegetarians. Therefore, a daily supplement of iron may be essential to maintaining a normal, healthy life. But not all iron supplements are created equal. Because of its higher solubility, a form of iron called “ferrous iron” is generally known to be more bioavailable and therefore more effective.