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More Calcium
Calcium is essential to a healthy diet, yet most
children and adolescents are not getting enough. In fact, only 14% of teen girls and 35%
of teen boys are meeting the 1989 Recommended Dietary Allowance (RDA).1
However, calcium is critical in building bone mass in order to support physical activity
throughout life and to reduce the risk of bone fracture, especially that due to
osteoporosis.
Although the consequences of low calcium consumption may not
be visible in childhood, the National Institute of Child Health and Human Development
(NICHD) recognizes this problem as a serious and growing threat to children and teens
later in life. At a time when they require more nutrients to feed their rapidly growing
and developing bodies, these children and teens are putting themselves at high risk.
Health professionals can help teens improve their nutrition habits; according to a recent
survey, doctors, parents, and teachers are their top sources for health and nutrition
information.2
The Role of Calcium
in Building Bone
Calcium plays a critical role in building strong and healthy
bones. Low calcium consumption and inadequate weight-bearing exercise contribute to
osteoporosis, the weakening of the bone that can occur late in adulthood and causes 1.5
million bone fractures a year. About 10 million Americans have osteoporosis. In addition,
an estimated 41 million Americans may develop osteoporosis or low bone mass by 2015 unless
steps are taken to prevent, detect, and treat the disease.
Two important factors that influence the incidence of
osteoporosis are peak bone mass attained during the first two to three decades of life and
the rate at which bone is lost in the later years.3 Childhood and adolescence
are critical periods for bone development because most bone mass accumulates during this
time. By the time adolescents finish their "growth spurt" around the age of 17,
approximately 90% of their adult bone mass will have been established. Bones then continue
to grow more dense until around age 30, when peak bone mass is reached. At this point,
bone mass and density may remain steady, or bone loss may begin to occur at a rate of up
to about 1% per year.
NICHD believes that osteoporosis is a pediatric preventable
disease. A recent NICHD-supported study found that supplementing the diets of girls, age
12-16, with 500 mg of calcium citrate-malate produced a 14% increase in bone density in
comparison to unsupplemented girls. The implications of this increase are striking: for
every 5% increase, the risk of fracture later in life declines by 40%. However, subsequent
study has shown that without continued supplementation at this level, the difference in
the bone densities of the two groups becomes indistinguishable.4 Therefore,
adequate growth, development, and maintenance of the skeletal system requires continuing
calcium intake over a lifetime.
Unfortunately, most children and teens do not meet the
dietary calcium recommendations that can help build maximum bone mass and protect against
osteoporosis. Half of all children under five and about 85% of females age 12-19 do not
meet the 1989 Recommended Dietary Allowance (RDA) for calcium. And even fewer of these
children and adolescents could attain the government's new guidelines, the Dietary
Reference Intakes (DRIs), set in 1997 (see Table 1).
These new guidelines set Adequate Intake (AI) values for
calcium designed to lead to the fewest diet-related osteoporotic fractures later in life.
Prior to the DRIs, optimal levels of calcium were recommended by the National Institutes
of Health (NIH) Consensus Conference in 1994 and were slightly higher for most age groups.
Parents should ensure that their children and teens get enough calcium and weight-bearing
exercise to help them reach their maximum bone density.
Table 1
| DAILY CALCIUM RECOMMENDATIONS VS. ACTUAL CONSUMPTION |
Age Group
|
1997 Adequate Intake Values1
|
1994 NIH Consensus Conference Recommendations2 |
1989 RDA Values3
|
Percentage of Children and Teens Meeting the 1989 RDA Values4 |
Birth to 6 months
|
210 mg
|
400 mg
|
400 mg |
Males Females
69.4
(males and females under 1) |
| 6-12 months |
270 mg |
600 mg |
600 mg |
45.4
(males and females under 5) |
| 1-3 years |
500 mg |
800 mg |
800 mg |
45.4
(males and females under 5) |
| 4-8 years |
800 mg |
800 mg |
800 mg |
|
| 9-13 years |
1,300 mg |
800-1,200 mg
(6-10 years) |
800 mg
(6-10 years) |
53.3 43.1
(6-11 years) (6-11 years) |
| 14-18 years |
1,300 mg |
1,200-1,500 mg
(11-24 years) |
1,200 mg
(11-24 years) |
35.1 14.4
(12-19 years) (12-19 years) |
| Lactating teens |
1,300 mg
(under 18 years) |
1,200-1,500 mg |
1,200 mg |
NA NA |
| One 8 ounce glass of milk = 300 mg of calcium 1 Dietary Reference Intakes for Calcium, Phosphorus, Magnesium,
Vitamin D, and Fluoride,
The National Academy of Sciences, 1997.
2 NIH Consensus Conference Statement on Optimal Calcium Intake, 1994.
3 Recommended Dietary Allowances, National Research Council, 1989.
4 USDA Continuing Survey of Food Intakes by Individuals, 1994, Table 3: Percentage of
Individuals
Meeting 100 Percent of the 1989 Recommended Dietary Allowances, 2 day average, 1994. |
QUESTIONS
AND ANSWERS ABOUT CALCIUM INTAKE
Q: How does
bioavailability affect calcium absorption?
A: Bioavailability is the degree to which the
intestinal system can absorb calcium. Absorption depends on the overall level of calcium
in the food and the type of food being consumed. Foods vary in their ability to enhance or
inhibit calcium absorption. The efficiency of calcium absorption is fairly similar for
foods such as dairy products and grains. However, calcium may be poorly absorbed in foods
high in oxalic acid (spinach, sweet potatoes, and beans) or phytic acid (unleavened bread,
raw beans, seeds, and nuts). Oxalates in particular are strong inhibitors of calcium
absorption. As a result, additional servings of many calcium-rich foods are needed to
compensate for their low calcium absorption. According to the National Academy of Sciences
report on the new DRIs, the body absorbs about a tenth as much calcium from spinach as it
does from milk.
Q: What other
factors can affect bone development?
A: Vitamin D - Vitamin D is an essential factor in bone mineralization, assisting
in calcium absorption. Vitamin D acts to increase absorption from the gastrointestinal
tract by encouraging active transport of calcium through the epithelium of the ileum.5
Deficiencies of this vitamin are responsible for serious abnormalities in the
mineralization of newly formed bone and result in reduced absorption.
Physical Activity - Weight bearing activity determines
the strength, shape, and mass of bone. Activities such as running, jumping, and dancing,
as well as those that increase strength, can help bone development. Studies show that
absence of exercise will result in a loss of bone mass, especially during long periods of
immobilization.
Table 2
| Food |
Serving Size |
Calcium |
Servings Needed to = 1 cup of Milk |
| Milk |
1 cup |
300 |
1.0 |
| Spinach |
1/2 cup |
122 |
15.5 |
| Beans, red |
1/2 cup |
40 |
14.0 |
| Broccoli |
1/2 cup |
35 |
5.2 |
| Green Cabbage |
1/2 cup |
25 |
5.9 |
| Kale |
1/2 cup |
47 |
3.5 |
| Turnip greens |
1/2 cup |
99 |
1.9 |
| Mustard greens |
1/2 cup |
47 |
3.5 |
(Adapted from Weaver, C.M., and Plawecki, K.L. (1994).
Dietary Calcium: adequacy of a vegetarian diet. AM J Clin Nutr, 59(suppl):1240S) |
Q: Why choose milk as a
source of calcium?
A: While calcium can be found in a variety of
foods, including vegetables, grains, and dairy products, the 1994 NIH Consensus Conference
on Optimal Calcium Intake designated dairy products as the preferred source of calcium.6
The NICHD has selected low-fat or fat-free milk as the best source of calcium because it
has a high calcium content and the calcium can be easily absorbed by the body. Milk is
also a widely available dairy product already a part of many American diets.
In fact, milk products provide about 3/4 of the calcium in
the U.S. food supply. While other foods, such as green leafy vegetables, are healthy
sources of calcium, it takes 11-14 servings of kale a day to get the same amount of
calcium in 3-4 glasses of milk.
In addition to calcium, milk provides other essential
nutrients which are important for optimal bone health and human development including:
vitamins D, A, and B12; potassium, magnesium, protein, phosphorus, and riboflavin.
Q: How can drinking milk fit in as
part of a heart-healthy diet?
A: The NICHD encourages consumption of low-fat or fat-free milk rather than whole milk
after two years of age. No matter which type, milk contains about 300 mg of calcium per 8
oz glass. Incorporating low-fat and fat-free milk can be a great complement to a
heart-healthy diet while still providing an excellent source of calcium.
Q: At what age can children begin to
drink low-fat or fat-free milk?
A: The American Academy of Pediatrics recommends that children drink only breast milk or
iron-fortified formula during their first year. Because children under age two should not
have fat-restricted diets, children between the ages of one and two may begin to drink
whole milk. After age two, they should drink fat-free or low-fat milk.
Q: Aren't some people
lactose intolerant and unable to consume milk?
A: Recent controlled studies indicate that many of those who are lactose intolerant may
still consume smaller portions of milk products without suffering ill effects. In one
study of 30 people who classified themselves as severely lactose-intolerant, 9 were found
able to absorb lactose, and the other 21 could tolerate 240 ml per day over a week period.7
There are however, specific populations that are genetically
lactose intolerant, including about 85 percent of Asian- Americans and 50 percent of
African-Americans. Lactose intolerance is least common among people of northern European
origin, affecting only about 10% of Caucasians.8 It also occurs infrequently in
infants and young children. Studies have shown that lactase is high at birth in all
infants regardless of race, and wanes in non-Caucasians and other populations without
dairy traditionally in their diet by age 5-6.
There are some strategies for people who can not easily
digest lactose. Drinking milk in servings of one cup or less and drinking milk with other
food can diminish symptoms. Other dairy products, such as cheese or yogurt, can also be
easier to digest. In addition, lactose containing foods may also be treated with
commercial preparations of lactase.9 There are a variety of digestive aids,
including drops that can be added to milk, and tablets taken with lactose-containing
foods.
Q: Are there risks
associated with high calcium intake?
A: The 1997 DRIs set a Tolerable Upper Intake Level (UL) for calcium and other nutrients.
The UL is set at the highest level that is unlikely to pose adverse health risks to almost
all individuals. For calcium, the UL is 2,500 mg per day for all age groups, including
pregnant and lactating women. This level of calcium is far above the AI values recommended
for any age group and corresponds to an average of more than 8 glasses of milk a day. This
level is likely to be exceeded only by individuals who overuse calcium carbonate antacids.
The efficiency of calcium absorption decreases as intake increases, protecting the body
from absorbing too much calcium. In addition, there is an association between calcium and
oxalate and the formation of kidney stones. However, while certain foods can affect stone
formation in susceptible people, researchers do not believe eating any specific food
causes stones to form in people not susceptible.10
Q: Can children be given
calcium supplements to augment their calcium intake?
A: Experts believe calcium should be obtained from natural dietary sources whenever
possible. The 1994 NIH Consensus Conference Statement on Optimal Calcium Intake indicates
that dairy products are the best source of calcium and contain far more utilizable calcium
than other foods. However, if calcium cannot be ingested dietarily, calcium supplements
can be given to children. For optimal absorption, no more than 500 mg of supplemental
calcium should be taken at any one time. Children and young adults, who absorb calcium
relatively well, are perhaps best off taking calcium supplements between meals.
Q: Are there any special
recommendations for pregnant or lactating adolescents?
A: During pregnancy, approximately 25 to 30 grams of calcium are transferred to the fetus,
mostly during the third trimester. Although studies do not show conclusively that higher
calcium intake is needed during this time, pregnant adolescents may benefit from a high
calcium intake due to their need to support their own bone growth as well as that of the
fetus.
Increasing dietary calcium does not prevent the loss of
calcium that occurs during lactation, and the calcium lost seems to be regained following
weaning. Therefore, the DRIs do not recommend increasing calcium intake in lactating
adolescents above normal levels for that age group. However, the 1994 NIH Consensus
Conference statement recommends that lactating adolescents and young adults increase their
ingestion of calcium to up to 1,500 mg per day.
REFERENCES:
1 USDA Continuing Survey of Food Intakes by Individuals,
1994, Table 3.
2 National Teen Nutrition Research - Final Report. Teenage
Research
Unlimited, June 1996.
3 NIH Consensus Conference Statement: Optimal Calcium
Intake, June 6-8,
1994; 12(4): 3.
4 Lloyd, Tom et al. Calcium supplementation and bone mineral
density in
adolescent girls. JAMA 1993; 270(7): 841-844.
5 Guyton, A.C. Textbook of Medical Physiology, 8th Edition.
Philadelphia:
W.B. Saunders Company: 1996; 786.
6 NIH Consensus Conference Statement: Optimal Calcium
Intake, June 6-8,
1994; 12(4): 24.
7 Suarez, F.L., Savaiano, D., Arbisi, P., & Levitt, M.D.
Tolerance to the
daily ingestion of two cups of milk by individuals claiming lactose
intolerance. Am J Clin Nutr 1997; 65(5): 1502-6.
8 Dietary Reference Intakes for Calcium, Phosphorus,
Magnesium, Vitamin D,
and Fluoride. Food and Nutrition Board, Institute of Medicine.
Washington, DC: National Academy Press, 1997: 4-6.
9 Miller, G.D., Jarvis, J.K., McBean, L.D. Handbook of Dairy
Foods and
Nutrition. Boca Raton: CRC Press, 1995: 203-209.
10 Kidney Stones in Adults. National Institute of Diabetes
and Digestive
and Kidney Diseases, National Institutes of Health: April 1994.
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