Nutrition Science and Everyday Application - beta v 0.1

CALCIUM: CRITICAL FOR BONES AND THROUGHOUT THE BODY 507
Figure 9.6. Dietary sources of calcium. Examples of good sources pictured include cheese, milk,
fortified soymilk, yogurt (with almond granola), edamame, and chia seeds. Source: NIH Office of
Dietary Supplements and Dietary Guidelines for Americans, 2015-2020.
Calcium bioavailability, or the amount of dietary calcium that is absorbed from the
intestine into the bloodstream, can vary significantly. In general, calcium absorption is
highest in infants and young children—who need relatively high amounts of calcium for
building bone—and declines with age. With higher calcium intake, especially from
supplements, bioavailability decreases in order to prevent excessive calcium absorption.
Some chemical components of plant foods, including phytic acid (found in whole grains,
beans, seeds, soy, and nuts) and oxalic acid (found in spinach, collard greens, sweet
potatoes, rhubarb, and beans), bind to calcium and reduce bioavailability. Despite reduced
absorption, these foods can still provide a significant amount of calcium. 1
Calcium Deficiency and Toxicity
In the short-term, there are no obvious signs of calcium deficiency. This is because the body
stores so much calcium in bones, and just 1% of total body calcium is required for daily
functioning. If low blood calcium does occur, symptoms include muscle cramping, numbness
and tingling in fingers, convulsions, lethargy, poor appetite, and abnormal heart rhythms.
Without treatment, low blood calcium can lead to death. 1
Much more common is a long-term calcium deficiency, resulting from a continuous draw
of calcium stores from the bone. This causes osteopenia, or low bone mass, which can lead
to osteoporosis if untreated. Osteoporosis significantly increases a person’s risk of fractures.
Nutrition surveys in the United States show that groups at greatest risk of dietary calcium
inadequacy include adolescents and older adults, especially female teens and older women. 1
Too much calcium can also cause problems, although this is rarely caused by excessive
intake of calcium from foods. Abnormally high activity of the parathyroid gland or a