Oh, the things you can learn in school!

In Anatomy and Physiology this past week, we started our unit on the blood system. I’ve never spent any time in depth learning about blood, but I was pleasantly surprised to find that the subject was anything but boring.

In our discussion of red blood cells (RBC), the most abundant type of blood cells in the body, my professor of course spent a good deal of time talking about hemoglobin, the protein that enables RBC to serve as transport molecules for the oxygen our bodily tissues require. To illustrate the importance of hemoglobin, consider the fact that red blood cells are composed of 97% hemoglobin.

Each molecule of hemoglobin is made up of four globin protein chains. Each of a hemoglobin molecule’s four globin chains possesses a heme group, and each heme group in turn contains a charged iron atom. It is to this iron ion that oxygen binds.

When we humans breathe in, the oxygen that enters our lungs is loaded, molecule by molecule, onto these iron ion sites. Under ideal conditions, each hemoglobin molecule would be fully saturated with oxygen molecules; that is to say that the four iron ion sites of each hemoglobin molecule would be attached to four oxygen molecules.

As you may remember from high school biology, the energy currency of the body, ATP, is produced aerobically (in the presence of oxygen), by the cellular mitochondria, the energy “factories” of the body. Because red blood cells lack a nucleus and organelles, they have no such mitochondria and thus no way to aerobically produce ATP. This turns out to be advantageous, however, for the RBC. Because they have no need to use oxygen to make ATP, the RBC are able to conserve all of their oxygen and thus deliver a maximum number of oxygen molecules to the body cells.

Because it is to the iron sites in the hemoglobin that oxygen binds, you can imagine that iron is vital for the proper functioning of the body. Indeed, an iron deficiency is one of the most common forms of nutritional deficiencies, and has far-reaching implications beyond impairing oxygen transport.

Iron deficiencies can be caused by a variety of reasons, including chronic bleeding (e.g. as a result of a bleeding ulcer or excessive menstrual bleeding), acute blood loss (as caused by a car accident, for example), drugs that interfere with iron absorption and, most commonly, as a result of inadequate iron intake. Symptoms of iron deficiency include fatigue, paleness, weakness, brittle or grooved nails and irritability.

As someone who plans to pursue nutrition as a career path, it is of great interest to me to promote diets that contain adequate amounts of iron.

What, then, are good dietary sources of iron? Red meat, fish, poultry, lentils, beans and tofu are all good sources, as are dark leafy green vegetables and fortified breakfast cereals. Some iron can also be found in molasses.

As with most nutrients, iron from various dietary sources is absorbed and processed in different ways. Iron from meat (“heme iron source”) is more easily absorbed than the iron in grains and vegetables, for example. Because of this, vegetarians and vegans should take care to take in extra iron from their diets. Legumes and dark leafy greens are again good vegetarian and vegan sources of the nutrient, but spinach and Swiss chard unfortunately contain substances called oxalates that inhibit absorption of the very iron they contain. One solution to this is to consume vegetarian and vegan sources of iron with foods that contain Vitamin C, which enhances iron absorption.

Maybe Popeye should’ve taken his spinach with a tall glass of orange juice.

Happy Grubbin’!