Nutrition Science and Everyday Application - beta v 0.1

538 ALICE CALLAHAN, PHD, HEATHER LEONARD, MED, RDN, AND TAMBERLY POWELL, MS, RDN
pain. 1 The body excretes little iron; therefore, the potential for toxicity from supplements is
a concern. In children, death has occurred from ingesting as little as 200 mg of iron, so it is
critical to keep iron supplements out of children’s reach. The tolerable upper intake for iron
is 45 mg per day for adults, based on the amount that causes gastrointestinal distress. 1
VITAMIN K
Vitamin K refers to a group of fat-soluble vitamins that are similar in chemical structure. They
act as coenzymes and have long been known to play an essential role in blood coagulation
or clotting. Vitamin K is also required for maintaining bone health, as it modifies a protein
which is involved in the bone remodeling process.
Dietary Sources of Vitamin K
Vitamin K is found in the highest concentrations in green vegetables such as collard and
turnip greens, kale, broccoli, and spinach. Soybean and canola oil are also common sources
of vitamin K in the U.S. diet. 5 Additionally, vitamin K can be synthesized by bacteria in the
large intestine, but the bioavailability of bacterial vitamin K is unclear.
Figure 9.21. Dietary sources of vitamin K. Examples of good sources pictured include chard,
spinach, kale, broccoli, and soybean oil. Source: NIH Office of Dietary Supplements
Vitamin K Deficiency and Toxicity
Vitamin K deficiency is rare, as most U.S. diets are adequate in vitamin K. 5 A deficiency in
vitamin K causes excessive bleeding (or hemorrhage). When there is damage to a blood vessel