Calcium Requirements of Infants,
Children and Adolescents
Committee on Nutrition
ABSTRACT.
This statement is intended to provide pediatric caregivers with advice about
the nutritional needs of calcium of infants, children, and adolescents. It will
review the physiology of calcium metabolism and provide a review of the data
about the relationship between calcium intake and bone growth and metabolism.
In particular, it will focus on the large number of recent studies that have
identified a relationship between childhood calcium intake and bone
mineralization and the potential relationship of these data to fractures in
adolescents and the development of osteoporosis in adulthood. The specific
needs of children and adolescents with eating disorders are not considered.
Approximately
99% of total body calcium is found in the skeleton, with only small amounts
found in the plasma and extravascular fluid. Serum calcium exists in 3
fractions: ionized calcium (approximately 50%), protein-bound calcium
(approximately 40%), and a small amount of calcium that is complexed, primarily
to citrate and phosphate ions. Serum calcium is maintained at a constant level
by the actions of several hormones, most notably parathyroid hormone and
calcitonin. Calcium absorption is by the passive vitamin D-independent route or
by the active vitamin D-dependent route.1
Understanding
calcium needs for different age groups requires a consideration of the variable
physiologic requirements for calcium during development. For example, during
the first month of life, the regulatory mechanisms that maintain serum calcium
levels may not be entirely adequate in some otherwise healthy infants, and
symptomatic hypocalcemia can occur. However, in general, hypocalcemia is
uncommon in healthy children and adolescents, and the primary need for dietary
calcium is to enhance bone mineral deposition.
Calcium
requirements also are affected substantially by genetic variability and other
dietary constituents. The interactions of these factors make identification of
a single unique number for the calcium "requirement" for all children
impossible.2-4 However, several recent dietary guidelines have considered the
data about calcium requirements and recommended calcium intake levels that are
calculated to benefit most children (Table 1).2,3
In
addition to calcium intake, exercise is an important aspect of achieving
maximal peak bone mass. There is evidence that childhood and adolescence may
represent an important period for achieving long-lasting skeletal benefits from
regular exercise.5 For example, Welten et al6 showed in a large Dutch cohort of
children that regular weight-bearing activity had a greater influence on peak
bone mass than dietary calcium.
IDENTIFICATION
OF MINERAL REQUIREMENTS DURING CHILDHOOD
Overview
It is recognized that a very low calcium intake can contribute to the development
of rickets in infants and children, especially those consuming very restrictive
diets (eg, a macrobiotic diet).7 There are no reliable data on the
lowest calcium intake needed to prevent rickets or on the relationship among
ethnicity, vitamin D status, physical activity, and diet in the causation of
rickets in children fed low-calcium diets.8,9
Recent
data support the possibility that a low bone mass may be a contributing factor
to some fractures in children. A relationship between the adolescent growth
spurt and the risk of fractures has been shown.10,11 Goulding et al12
reported lower bone mass at multiple sites in a group of 100 girls aged 3 to 15
years with distal forearm fractures compared with age-matched girls. For girls
aged 11 to 15 years in the study by Goulding et al12
a lower calcium intake was reported for those with fractures compared with the
control subjects. Wyshak and Frisch13 similarly reported that high
calcium intakes seem to exert a protective effect against fractures in
adolescent boys and girls. They also reported a positive relationship between
cola beverage intake and bone fracture. Whether this is attributable to a
potential effect of excessive phosphorus in the colas impairing bone mineral
status or to the lack of calcium intake related to the substitution of colas
for dairy products is uncertain. However, a direct harmful effect of a high
phosphorus intake affecting the bone mineral status is unlikely in older
children and adults.2 Further data on the relationship
between calcium intake and fractures are needed before the magnitude of
increased fracture risk at different calcium intake levels can be assessed.
However, it is reasonable to conclude that low calcium intakes may be an
important risk factor for fractures in adolescents. This risk may be an issue
that adolescents can more readily relate to than a long-term risk of
osteoporosis.
Maintaining
adequate calcium intake during childhood is necessary for the development of a
maximal peak bone mass. Increasing peak bone mass may be an important way to
reduce the risk of osteoporosis in later adulthood.2,14 This is a
more difficult end point to identify than the development of rickets or
fractures. Therefore, surrogate markers of mineral status are used to assess
the consequences of differing levels of calcium intake. The primary surrogates
used are optimization of calcium balance or achievement of greater bone mass in
children with increased calcium intake.3,14,15
In
children with chronic illnesses, fractures may occur during childhood secondary
to mineral deficiency associated with the disease process or the effects of
therapeutic interventions (ie, corticosteroids) on calcium metabolism.16
However, minimal data generally are not available on the risks and benefits of
increasing calcium intake in children with chronic illnesses above current
dietary recommendations. Supplementation of vitamin D along with calcium may be
necessary for a maximal response.17
Methods
Multiple approaches are used to assess mineral
requirements in children. They include the following: 1) measurement of calcium
balance in persons with various levels of calcium intake; 2) measurement of
bone mineral content, by dual-energy radiograph absorptiometry or other
techniques, in groups of children before and after calcium supplementation; and
3) epidemiologic studies relating bone mass or fracture risk in adults with
childhood calcium intake.
The
calcium balance technique consists of measuring the effects of any given
calcium intake on the net retention of calcium by the body. This approach has
been the most commonly used to estimate requirement for minerals. Its
usefulness is based on the rationale that virtually all retained calcium must
be used, especially by children, to enhance bone mineralization. It therefore
is reasonable to expect that the dietary intake that leads to the greatest
level of calcium retention is the intake that will lead to the greatest benefit
for promoting skeletal mineralization and decreasing the ultimate risk of
osteoporosis.18,19
The
substantial limitations involved in obtaining and interpreting data about
calcium balance are well known. These include substantial technical problems
with measuring calcium excretion and the difficulty obtaining dietary intake
control in children. Both of these are necessary for adequate balance studies.
These problems have been partly overcome by the development of stable isotopic
methods to assess calcium absorption and excretion.20 Nevertheless, more data are needed to establish the
"optimal" level of calcium retention at different ages and the
effects of development on calcium balance.6
A
major advance in the field during the last 25 years has been the development
and improvement of methods to measure total body and regional bone mineral
content by using various bone density techniques. Currently, the technique used
in many studies is dual-energy radiograph absorptiometry. This technique can
rapidly measure the bone mineral content and bone mineral density of the entire
skeleton or of regional sites with a virtually negligible level of radiation
exposure. Furthermore, recent enhancements in the precision of the technique
have made it particularly suitable for assessing the effects of calcium
supplementation on bone mass in children of all ages.21
Several
groups have directly assessed the effects of calcium supplementation on bone
mass by using dual-energy radiograph absorptiometry or similar techniques.22-25
These studies, however, also have limitations. First, most supplementation studies done in children involved
relatively short-term supplementation of 1 to 2 years. This period may
be inadequate to fully assess the long-term benefits of calcium supplements on
bone mineral density. The second is that these studies generally have been done
using only 1 level of supplementation, which frequently has been given in pill
form. This limited dosing approach makes it difficult to identify an optimal
intake level or determine the relative benefits of dietary calcium versus
supplements as a method of increasing calcium intake in children.
Several
investigators have performed population-based epidemiologic studies relating
childhood or adult bone mass or fracture risk to calcium intake in childhood.
Although many of these studies are limited by their retrospective design, they
have generally shown a positive association between calcium intake in childhood
and childhood and adult bone mass. Not all studies have shown a benefit,
however, and further data about this relationship are needed.3,26-28
RECOMMENDATIONS
BY AGE GROUP
Overview
The specific requirements for calcium intake by
infants, children, and adolescents have been extensively reviewed by 2 panels
in
Infants
The optimal primary nutritional source during the
first year of life is human milk. No available evidence shows that exceeding
the amount of calcium retained by the exclusively breastfed term infant during
the first 6 months of life or the amount retained by the human milk-fed infant
supplemented with solid foods during the second 6 months of life is beneficial
to achieving long-term increases in bone mineralization. Available data
demonstrate that the bioavailability of calcium from human milk is greater than
that from infant formulas or cow's milk, although this comparison has not
generally been made at comparable intake concentrations, ie, such as found in
human milk.29 Nevertheless, it has been deemed prudent to increase
the concentration of calcium in all infant formulas relative to human milk to
ensure at least comparable levels of calcium retention. Relatively greater
calcium concentrations are found in specialized formulas, such as soy formulas
and casein hydrolysates, to account for the potential lower bioavailability of
the calcium from these formulas relative to cow's milk-based formula. Specific
concentration requirements cannot be set readily, but all formulas marketed
should have demonstrated a net calcium retention at
least comparable to that of human milk. Research data are not available to
justify the use of very high levels of calcium in infant formula for full-term
infants.
Premature
infants have higher calcium requirements than full-term infants while in the
nursery. These may be met by using human milk fortified with additional
minerals or with specially designed formulas for premature infants.30 After
hospitalization, there may be benefits to providing formula-fed premature
infants formulas with higher calcium concentrations than those of routine cow's
milk-based formulas.31 The optimal concentrations and length of time
needed for such formulas are unknown.
Children
Few data are available about the calcium requirements
of children before puberty. Calcium retention is relatively low in toddlers and
slowly increases as puberty approaches. Most available data indicate that
calcium intake levels of about 800 mg/d are associated with adequate bone
mineral accumulation in prepubertal children. The benefits of greater levels of
intake in this age group have been studied inadequately.20,32 One
study found a benefit of calcium supplements to children as young as 6 years of
age.16 However, further supporting data are needed for this finding.
Perhaps of most importance in this age group is the development of eating
patterns that will be associated with adequate calcium intake later in life.
Preadolescents
and Adolescents
The majority of research in children about calcium
requirements has been directed toward 9- to 18-year-olds. The efficiency of
calcium absorption is increased during puberty, and the majority of bone
formation occurs during this period.15,20,21,32,33
Data from balance studies suggest that for most healthy children in this age
range, the maximal net calcium balance (plateau) is achieved with intakes
between 1200 and 1500 mg/d. That is, at intake levels above this, almost all of
the additional calcium is excreted and not used. At intakes below that level,
the skeleton may not receive as much calcium as it can use, and peak bone mass
may not be achieved.2,3,9,15,18-20 Virtually all the data used to
establish this intake level are from white children; minimal data are available
for other ethnic groups. The exact level that is best for a given person
depends on other nutrients in the diet, genetics, exercise, and other factors.
Several
controlled trials have found an increase in the bone mineral content in
children in this age group who have received calcium supplementation.22-25
However, the available data suggest that if calcium is supplemented only for
relatively short periods (ie, 1 to 2 years), there may not be long-term
benefits to establishing and maintaining a maximum peak bone mass.34,35
This emphasizes the importance of diet in achieving adequate calcium intake and
in establishing dietary patterns consistent with a calcium intake near
recommended levels throughout childhood and adolescence. Unfortunately,
long-term studies evaluating the consequences of maintaining currently
recommended calcium intakes beginning in childhood or early adolescence are not
available. Most available epidemiologic data, recently reviewed by the National
Academy of Sciences and the National Institutes of Health, support the view
that maintaining such a diet will increase peak bone mass and lower the
incidence of fractures.2,3
Recent
data obtained in African American adolescents suggest a link between lower
diastolic blood pressure and increased calcium intake. Further studies are
necessary to evaluate this relationship in children of multiple ethnicities and
age groups.36
ACHIEVING
RECOMMENDED INTAKES
The
gap between the recommended calcium intakes and the typical intakes of
children, especially those 9 to 18 years of age, is substantial (Table 1). Mean
intakes in this age group are between approximately 700 and 1000 mg/d, with
values at the higher side of this range occurring in males.3
Preoccupation with being thin is common in this age group, especially among
females, as is the misconception that all dairy foods are fattening. Many
children and adolescents are unaware that low-fat milk contains at least as
much calcium as whole milk.
Knowledge
of dietary calcium sources is a first step toward increasing the intake of
calcium-rich foods. Table 2 gives typical amounts of calcium for some common
food sources. The largest source of dietary calcium for most persons is milk
and other dairy products.37 Other sources
of calcium are, however, important, especially for achieving calcium intakes of
1200 to 1500 mg/d. Most vegetables contain calcium, although at low density.
Therefore, relatively large servings are needed to equal the total intake
achieved with typical servings of dairy products. The bioavailability of
calcium from vegetables is generally high. An exception is spinach, which is
high in oxalate, making the calcium virtually nonbioavailable. Some
high-phytate foods, such as whole bran cereals, also may have poorly bioavailable calcium.38-40
Several
products have been introduced that are fortified with calcium. These products,
most notably orange juice, are fortified to achieve a calcium concentration
similar to that of milk. Limited studies of the bioavailability of the calcium
in these products suggest that it is at least comparable to that of milk.41
It is likely that more such products will soon become
available. Breakfast foods also are frequently fortified with minerals,
including calcium. Calcium intakes on food labels are indicated as a percentage
of the "daily value" in each serving. This daily value is currently
set as 1000 mg/d. Therefore, it is important to instruct families about reading
and interpreting food labels.
Several
alternatives exist for children with lactose intolerance. Lactose intolerance
is more common in African Americans, Mexican Americans, and AsianPacific
Islanders than in whites.42 Many children
with lactose intolerance can drink small amounts of milk without discomfort.
Other alternatives include the use of other dairy products, such as solid
cheeses and yogurt, that may be better tolerated than
milk. Lactose-free and low-lactose milks are available. Increasing the intake
of nondairy products, such as vegetables, may be helpful, as may the use of
calcium-supplemented foods.
For
children and adolescents who cannot or will not consume adequate amounts of
calcium from any dietary sources, the use of mineral supplements should be
considered. Although supplements vary in their bioavailability, they may have
bioavailability comparable to or greater than that of dairy products.43
Decisions about their use must be made on an individual basis, keeping in mind
the usual dietary habits of the person, any individual risk factors for
osteoporosis, and the likelihood that the use of the supplement will be
maintained.
CONCLUSION
Recent
studies and dietary recommendations have emphasized the importance of adequate
calcium nutriture in children, especially those undergoing the rapid growth and
bone mineralization associated with pubertal development. The current dietary
intake of calcium by children and adolescents is well below the recommended
optimal levels. The available data support recent recommendations for calcium
intakes of 1200 to 1500 mg/d beginning during the preteen years and continuing
throughout adolescence as recommended by the National Institutes of Health
Consensus Conference2 and the National Academy of Sciences.3
Currently, evidence is inadequate to alter the dietary recommendations for
children with chronic illnesses or those taking medications, such as
corticosteroids, that alter bone metabolism. However, an effort should be made
to achieve at least the recommended intake levels. The provision of adequate
vitamin D also may be important for children with chronic illnesses.
RECOMMENDATIONS
1. Pediatricians should
actively support the goal of achieving calcium intakes in children and
adolescents comparable to those in recently recommended guidelines.2,3
The prevention of future osteoporosis, as well as the possibility of a
decreased risk of childhood and adolescent fractures, should be discussed as
potential benefits to achieving these goals. Currently, relatively few children
and adolescents achieve dietary calcium intake goals.
2. To emphasize the importance
of calcium nutriture, pediatricians should consider including the following
questions about dietary calcium intake.
o
What
do you drink, either white or chocolate milk, with your meals?
o
Do
you drink milk with meals, snacks, or cereal or any other time during the day?
o
Do
you eat cheese, yogurt, or other dairy products such as cottage cheese?
o
Do
you drink calcium-fortified juices or eat any calcium-fortified foods?
o
Do
you eat any of the following: broccoli, tofu, oranges, or legumes (dried beans
and peas)?
o
Do
you take any mineral or vitamin supplements?
3. For children and adolescents
whose calcium intake seems deficient, specific information about the sources of
dietary calcium should be provided. Adolescents may need to be reminded that
low-fat dairy products, including skim milk and low-fat yogurts, are good
sources of calcium that are not high in fat.
TABLE 1
Dietary Calcium Intake (mg/d) Recommendations in the United States2,3*
|
Age |
1997 NAS3 |
1994 NIH2 |
|
0 to 6 mo† |
210 |
400 |
|
6 mo to 1 y† |
270 |
600 |
|
1 through 3 y |
500 |
800 |
|
4 through 8 y |
800 |
800 (4-5 y) |
|
|
|
800-1200 (6-8 y) |
|
9 through 18 y |
1300 |
800-1200 (9-10 y) |
|
|
|
1200-1500 (11-18 y) |
* Recommended intakes were
provided in different forms by each source cited. The Food and Nutrition Board
of the National Academy of Sciences (NAS) released Recommended Dietary
Allowances until 1997. In 1997, it chose to use the term adequate intake for
the recommendations for calcium intake but indicated that these values were to
be used as Recommended Dietary Allowances. The NIH Consensus Conference did not
specify a specific term but indicated that these values were the
"optimal" intake levels. Dietary recommendations by the NAS are set
to meet the needs of 95% of the identified population of healthy subjects. The NAS
guideline should be the primary guideline utilized. † For infant values, the
1994 NIH Consensus Conference indicated values for formula-fed infants, whereas
the 1997 NAS report used the infant fed human milk as the standard.
TABLE
2
Approximate Calcium Contents of 1 Serving of Some Common Foods*
|
Food |
Serving Size |
Calcium Content |
|
|
Milk† |
1 cup |
240 mL |
300 mg |
|
White beans |
1/2 cup |
110 g |
113 mg |
|
Broccoli cooked |
1/2 cup |
71 g |
35 mg |
|
Broccoli raw |
1 cup |
71 g |
35 mg |
|
Cheddar cheese |
1.5 oz |
42 g |
300 mg |
|
Low-fat yogurt |
8 oz |
240 g |
300-415 mg |
|
Spinach cooked‡ |
1/2 cup |
90 g |
120 mg |
|
Spinach raw‡ |
1-1/2 cup |
90 g |
120 mg |
|
Calcium-fortified orange juice |
1 cup |
240 mL |
300 mg |
|
|
1 medium |
1 medium |
50 mg |
|
Sardines or salmon withbones |
20 sardines |
240 g |
50 mg |
|
Sweet potatoes |
1/2 cup mashed |
160 |
44 |
* Adapted from Raper
et al,37 Weaver,38,39 and Weaver and Plawecki.40
† Low-fat milk has comparable or greater calcium levels than whole milk.
‡ The calcium from spinach is essentially nonbioavailable.
COMMITTEE ON
NUTRITION, 1998-1999
Susan S. Baker, MD, PhD, Chairperson
William J. Cochran, MD
Carlos A. Flores, MD
Michael K. Georgieff, MD
Marc S. Jacobson, MD
Tom Jaksic, MD, PhD
Nancy F. Krebs, MD
LIAISON REPRESENTATIVES
Donna Blum-Kemelor, MS, RD
US Department of Agriculture
William Dietz, MD, PhD
Centers for Disease Control and Prevention
Gilman Grave, MD
National Institute of Child Health and Human
Development
Suzanne S. Harris, PhD
International Life Sciences Institute Van S. Hubbard, MD, PhD
National Institute of Diabetes and Digestive and
Kidney Diseases
Ann Prendergast, RD, MPH
Maternal and Child Health Bureau
Alice E. Smith, MS, RD
American Dietetic Association
Elizabeth Yetley, PhD
Food and Drug Administration
Doris E. Yuen, MD, PhD
Canadian Paediatric Society
SECTION LIAISONS
Scott C. Denne, MD
Section on Perinatal Pediatrics
Ronald M. Lauer, MD
Section on Cardiology
CONSULTANT
Steven A. Abrams, MD
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Pediatrics Volume 104,
Number
The recommendations in
this statement do not indicate an exclusive course of treatment or serve as a
standard of medical care. Variations, taking into account individual
circumstances, may be appropriate.
© Copyright 1999 American Academy
of Pediatrics
No part of this statement may be reproduced in any form or by any means without
prior written permission from the American Academy of Pediatrics except for one
copy for personal use.