Encyclopedia of Diets - A Guide to Health and Nutrition

again by cells called osteoblasts. This process is called
bone remodeling, and it continues throughout an indi-
vidual’s life. When excess calcium is present in the blood,
osteoblasts deposit calcium into bones. When too little
calcium is in the blood, osteoblasts dissolve calcium
from bones and move it into the blood. This process is
controlled by parathyroid hormone (PTH) secreted by
the parathyroid glands. The parathyroid glands are
extremely sensitive to the level of calcium in the blood,
andinahealthyindividualthey are able to maintain the
concentration of calcium ions fluctuates very little.

Normal calcium requirements
The United States Institute of Medicine (IOM) of
the National Academy of Sciences has developed val-
ues calledDietary Reference Intakes(DRIs) for many
vitaminsandminerals. The DRIs consist of three sets
of numbers. The Recommended Dietary Allowance
(RDA) defines the average daily amount of the
nutrient needed to meet the health needs of 97–98%
of the population. The Adequate Intake (AI) is an
estimate set when there is not enough information to
determine an RDA. The Tolerable Upper Intake Level
(UL) is the average maximum amount that can be
taken daily without risking negative side effects. The
DRIs are calculated for children, adult men, adult
women, pregnant women, andbreastfeedingwomen.

The IOM has not set RDAs for calcium, but
instead it has set AI levels for all age groups based
on observed and experimental information. However,
many studies show that Americans across almost all
age groups are not meeting these AI levels. One large
study, the Continuing Survey of Food Intakes of Indi-
viduals, found that in children ages 6–11 44% of boys
and 58% of girls were getting lower than recom-
mended amounts of calcium. In adolescents ages 12–
19, the rate of deficiency was higher—64% for boys
and a huge 87% for girls. Adults over age 20 did not do
much better with 55% of men and 78% of women
taking in less calcium than recommended. IAs and
ULs for calcium are measured in milligrams (mg).
The following list gives the recommended AL and
UL levels of calcium for each age group.

children birth–6 months: AI 210 mg; UL not
established;.

children 7–12 months: AI 270 mg; UL not established.

children 1–3 years: AI 500 mg; UL 2,500 mg

children 4–8 years: AI 800 mg; UL 2,500 mg

children 9–13 years: RDA 9 mg; UL 2,500 mg

adolescents 14–18 years: IA 1,300 mg; UL 2,500 mg

adults age 19–50: RDA 1,000 mg; UL 2,500 mg

adults over age 50: RDA 1,200 mg; UL 2,500 mg

pregnant women 18 years and younger: RDA 1,300

mg; UL 2,500 mg

pregnant women over age 18: RDA 1,000 mg; UL

2,500 mg

breastfeeding women 18 years and younger: RDA

1,300 mg; UL 2,500 mg

breastfeeding women over age 18: RDA 1,000 mg;

2,500 mg

Sources of calcium

In the United States, dairy products—milk, yogurt,

and cheese—are the main sources of dietary calcium.

Low-fat dairy products, such as skim milk or reduced-

fat cheese, contain about the same amount of calcium

as whole milk products. Other sources of calcium

include canned fish with bones, dark green leafy vege-

tables, and tofu made with calcium sulfate. Other types

of tofu do not contain significant amounts of calcium.

Processed foods such as orange juice, breakfast cereal,

instant breakfast drinks, and bread are often fortified

with calcium. This will be indicated on the label.

The following list gives the approximatemanga-

nesecontent for some common foods:

milk, any type, 1 cup (8 ounces): 300 mg

yogurt, plain, 8 ounces: 415 mg

yogurt with fruit, 8 ounces: 245–384 mg

KEY TERMS

Dietary supplement—A product, such as a vitamin,

mineral, herb, amino acid, or enzyme, that is

intended to be consumed in addition to an individ-

ual’s diet with the expectation that it will improve

health.

Diuretic—A substance that removes water from the

body by increasing urine production.

Electrolyte—Electrically charged particles (ions) that

form when salts dissolve in water or fluids. Electro-

lytes regulate water balance in the body and play a

critical role in almost every metabolic reaction.

Enzyme—Proteins that change the rate of a chem-

ical reaction within the body without themselves

being used up in the reaction.

Mineral—An inorganic substance found in the earth

that is necessary in smallquantities for the body to

maintain a health. Examples: zinc, copper, iron.

Calcium