Nutrition Science and Everyday Application - beta v 0.1

506 ALICE CALLAHAN, PHD, HEATHER LEONARD, MED, RDN, AND TAMBERLY POWELL, MS, RDN
Figure 9.5. Blood calcium (Ca 2+ ) levels are tightly regulated by PTH, vitamin D, and calcitonin.
Through these two opposing pathways—PTH and vitamin D for raising blood calcium and
calcitonin for lowering blood calcium—the body can very effectively maintain blood calcium
homeostasis. This system is dependent upon stored calcium in bone, which is sacrificed
when needed to ensure adequate blood calcium. In the short-term, this isn’t a problem,
because bone remodeling allows you to replace calcium in the bone. However, in the longterm,
inadequate dietary calcium means you continuously draw down the calcium stores in
your bones, resulting in declining bone mineral density and increased risk of fracture.
Calcium requirements are highest for children and adolescents, who are growing and
building bones, and for older adults, who are losing bone density. The RDA for calcium for
children 9 to 13 years old and teens 14 to 18 years old is 1,300 milligrams per day. The RDA
for adults is 1,000 mg per day but increases to 1,200 mg per day for women ages 51 and up
and for men age 71 and older.
Dietary Sources of Calcium
In the typical American diet, calcium is obtained mostly from dairy products. A slice of
cheddar or Swiss cheese contains over 200 milligrams of calcium. One cup of milk contains
approximately 300 milligrams of calcium, which is about a third of the RDA for calcium
for most adults. Foods fortified with calcium such as cereals, soy milk and other plantbased
beverages, and orange juice also provide one third or greater of the calcium RDA.
Smaller amounts of calcium are naturally present in plant-based foods such as legumes,
leafy greens, and nuts, and with careful planning, adequate calcium can be obtained from
non-dairy sources.