The steel cable of a colliery winding tower. Steel is an alloy of iron and other elements, primarily carbon, that is widely used in construction and other applications because of its high tensile strength and low cost. Steel's base metal is iron, which is able to take on two crystalline forms (allotropic forms), body centered cubic and face centered cubic (FCC), depending on its temperature.
: Appendix B: Vitamin and Mineral Deficiencies in the U.S. Some American adults get too little vitamin D, vitamin E, magnesium, calcium, vitamin A and vitamin C (Table B1). More than 40 percent of adults have dietary intakes of vitamin A, C, D and E, calcium and magnesium below the average requirement for their age and gender. Inadequate intake of vitamins and minerals is most common among 14-to-18-year-old teenagers. Adolescent girls have lower nutrient intake than boys (Berner 2014; Fulgoni 2011). But nutrient deficiencies are rare among younger American children; the exceptions are dietary vitamin D and E, for which intake is low for all Americans, and calcium.
  Although adolescence spans a period of five to seven years, teens do most of their growing during an 18-24 month period called the growth spurt.. To support this rapid growth, teenagers need to consume lots of calories and other nutrients.    Calories   Teenagers need lots of calories to support rapid growth. Girls need approximately 2200 calories, while boys need 2500-2900 calories. vitamins Large amounts of the B vitamins thiamin, riboflavin, and niacin are needed to meet the energy requirements of teens. Dietary Choices The desire for independence is a defining characteristic of the teenage years. One of the ways that teenagers assert their independence is through their dietary choices.