A Brief Overview of Minerals in Nutrition
Over the course of the history of the Earth, shifting oceans and plate tectonics have deposited minerals throughout the Earth’s crust. These minerals move from rocks to soil to plants and finally to animals and people. Nutrition focuses on mineral elements: single atoms that are simple compared to the large and complex vitamins. Nevertheless, minerals perform a wide variety of metabolic tasks that are essential to human life.
Classes of Minerals
Minerals occur in varying amounts in the body. For example, a relatively large amount of our total body weight is calcium (approximately 2.25 lbs), most of which is in the bones. On the other hand, iron is found in much smaller quantities (approximately 0.11 oz). The two classes of minerals are major minerals and trace minerals, classified based on their recommended intake.
Major Minerals
The term major describes the amount of a mineral in the body and not its relative importance to human nutrition. Major minerals have a recommended intake of more than 100 mg/day. The seven major minerals are calcium, phosphorus, sodium, potassium, magnesium, chloride, and sulfur. The body cannot make minerals, thus, all minerals must be consumed in the diet.
Trace Minerals
These minerals are no less important to human nutrition than the major minerals; however, smaller amounts of them are in the body. Trace minerals have a recommended intake of less than 100 mg/day. Trace minerals include iron, iodine, zinc, selenium, fluoride, copper, manganese, molybdenum, cobalt, boron, vanadium, and nickel. Note that the chromium essentiality of chromium is currently under review.
Functions of Minerals
Minerals are involved in most of the body’s metabolic processes. They are involved in processes of building tissue as well as activating, regulating, transmitting, and controlling metabolic processes. Sodium and potassium are key players in water balance. Calcium and phosphorus are required for osteoblasts to build bone. Iron is critical to the oxygen carrier hemoglobin. Cobalt is at the active site of vitamin B12. Thyroid peroxidase in thyroid cells uses iodine to make thyroid hormone, which in turn helps regulate the overall rate of body metabolism.
Mineral Metabolism
Mineral metabolism is usually controlled either at the point of intestinal absorption or at the point of tissue uptake.
Digestion
Minerals are absorbed and used in the body in their ionic forms, which means that they are carrying either a positive or a negative electrical charge. Unlike the macronutrients (carbohydrates, protein, lipids), minerals do not require a great deal of mechanical or chemical digestion before absorption occurs.
Absorption & Transport
The following general factors influence how much of a mineral is absorbed into the body from the gastrointestinal tract:
- food form — minerals from animal sources are usually more readily absorbed than those from plant sources
- body need — more is absorbed if the body is deficient than if the body has sufficient quantities
- tissue health — if the absorbing intestinal surface is affected by disease, its absorptive capacity is greatly diminished
The absorptive method of each mineral depends on its physical properties. Some minerals require active transport (requires energy) to be absorbed, whereas others enter the intestinal cells by diffusion (doesn’t require energy). Certain compounds, such as fiber, phytate, or oxalate (all of which are found in a variety of whole grains, fruits, and vegetables), can bind certain minerals in the GI tract, thus inhibiting or limiting their absorption. Minerals enter the portal blood circulation and travel throughout the body bound to plasma proteins or mineral-specific transport proteins.
Mineral Supplementation
Specific needs during growth periods and in clinical situations may merit specific mineral supplements. Before taking supplements, potential nutrient-nutrient and drug-nutrient interactions should be considered. Mineral supplements may be warranted in specific situations during rapid growth periods throughout the life cycle.
Pregnancy
During pregnancy, women require additional copper, iodine, iron, magnesium, manganese, molybdenum, selenium, zinc, and possibly chromium to meet the demands of rapid fetal growth.
Adolescence
Rapid bone growth during adolescence requires increased calcium, phosphorus, and magnesium. If an adolescent’s diet is chronically lacking in the minerals critical for bone development at this vital stage, the risk for osteoporosis during the later adult years is intensified. With the major increases in soft-drink consumption coupled with the decreased intake of calcium-containing drinks in the United States, there is cause for concern about poor bone growth during these important years. Depending on the adequacy of their diet, supplements that combine iron with folate may be indicated for adolescent girls as they begin menstruating.
Vegetarianism & Veganism
Due to the low zinc content and bioavailability found in plant foods, there is an increasing concern about possible zinc deficiency among vegetarians and vegans. The position statement of the Academy of Nutrition and Dietetics and the Dietitians of Canada regarding vegetarian and vegan diets indicates that zinc requirements for individuals who consume high phytate diets may exceed the current DRIs. Signs of zinc deficiency include slow growth, impaired taste and smell, poor wound healing, and skin irritation; however, 3–24 weeks may pass before symptoms appear.
Takeaway
Minerals are elements widely distributed in foods and are classified in accordance with their relative amounts in the body. RDAs have not been set for all minerals due to a lack of scientific data, and mineral supplementation continues to be a hot topic of research. Always consult a physician or registered dietitian before taking any kind of dietary supplement.
