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NCP Miracle II
161 Richardson-Bass Rd
Kenly, NC 27542
Tel:(919)284-6002 Fax:(919)284-4197
EMail: info1@ncpmiracle2.com
161 Richardson-Bass Rd
Kenly, NC 27542
Tel:(919)284-6002 Fax:(919)284-4197
EMail: info1@ncpmiracle2.com
| Calcium |
Calcium, the most abundant mineral in the human body, has several important functions. More
than 99% of total body calcium is stored in the bones and teeth where it functions to support their
structure [1]. The remaining 1% is found throughout the body in blood, muscle, and the fluid between
cells. Calcium is needed for muscle contraction, blood vessel contraction and expansion, the
secretion of hormones and enzymes, and sending messages through the nervous system [2]. A
constant level of calcium is maintained in body fluid and tissues so that these vital body processes
function efficiently.
Bone undergoes continuous remodeling, with constant resorption (breakdown of bone) and
deposition of calcium into newly deposited bone (bone formation) [2]. The balance between bone
resorption and deposition changes as people age. During childhood there is a higher amount of
bone formation and less breakdown. In early and middle adulthood, these processes are relatively
equal. In aging adults, particularly among postmenopausal women, bone breakdown exceeds its
formation, resulting in bone loss, which increases the risk for osteoporosis (a disorder characterized
by porous, weak bones) [2].
What is the recommended intake for calcium?
Recommendations for calcium are provided in the Dietary Reference Intakes (DRIs) developed by the
Institute of Medicine (IOM) of the National Academy of Sciences. Dietary Reference Intake (DRI) is the
general term for a set of reference values used for planning and assessing nutrient intakes of
healthy people. Three important types of reference values included in the DRIs are Recommended
Dietary Allowances (RDA), Adequate Intakes (AI), and Tolerable Upper Intake Levels (UL). The RDA
recommends the average daily intake that is sufficient to meet the nutrient requirements of nearly all
(97-98%) healthy individuals in each age and gender group. An AI is set when there is insufficient
scientific data available to establish a RDA. AIs meet or exceed the amount needed to maintain a
nutritional state of adequacy in nearly all members of a specific age and gender group. The UL, on
the other hand, is the maximum daily intake unlikely to result in adverse effects. It is listed in the
section "Is there health risk of too much calcium?" of this fact sheet.
For calcium, the recommended intake is listed as an Adequate Intake (AI), which is a recommended
average intake level based on observed or experimentally determined levels.
• What foods provide calcium?
In the United States (U.S.), milk, yogurt and cheese are the major contributors of calcium in the
typical diet [4]. The inadequate intake of dairy foods may explain why some Americans are deficient in
calcium since dairy foods are the major source of calcium in the diet [4]. The U.S. Department of
Agriculture's Food Guide Pyramid recommends that individuals two years and older eat 2-3 servings
of dairy products per day. A serving is equal to:
• 1 cup (8 fl oz) of milk
• 8 oz of yogurt
• 1.5 oz of natural cheese (such as Cheddar)
• 2.0 oz of processed cheese (such as American)
A variety of non-fat and reduced fat dairy products that contain the same amount of calcium as
regular dairy products are available in the U.S. today for individuals concerned about saturated fat
content from regular dairy products.
Although dairy products are the main source of calcium in the U.S. diet, other foods also contribute
to overall calcium intake. Individuals with lactose intolerance (those who experience symptoms such
as bloating and diarrhea because they cannot completely digest the milk sugar lactose) and those
who are vegan (people who consume no animal products) tend to avoid or completely eliminate dairy
products from their diets [2]. Thus, it is important for these individuals to meet their calcium needs
with alternative calcium sources if they choose to avoid or eliminate dairy products from their diet.
Foods such as Chinese cabbage, kale and broccoli are other alternative calcium sources [2].
Although most grains are not high in calcium (unless fortified), they do contribute calcium to the diet
because they are consumed frequently [2]. Additionally, there are several calcium-fortified food
sources presently available, including fruit juices, fruit drinks, tofu and cereals. Figure 1 compares
portion sizes of various foods that provide the amount of calcium in one cup of milk. This figure
takes into account that calcium absorption varies among foods. Certain plant-based foods such as
some vegetables contain substances which can reduce calcium absorption. Thus, you may have to
eat several servings of certain foods such as spinach to obtain the same amount of calcium in one
cup of milk, which is not only calcium-rich but also contains calcium in an easily absorbable form.
Table 2 contains additional listings of food sources of calcium.
• Helping hints for meeting your calcium needs
As the 2000 Dietary Guidelines for Americans states, "Different foods contain different nutrients and
other healthful substances. No single food can supply all the nutrients in the amounts you need" [9].
For more information about building a healthful diet, refer to the Dietary Guidelines for Americans
http://www.usda.gov/cnpp/DietGd.pdf and the US Department of Agriculture's Food Guide Pyramid
http://www.nal.usda.gov/fnic/Fpyr/pyramid.html [9,10].
The following are strategies and tips to help you meet your calcium needs each day:
• Use low fat or fat free milk instead of water in recipes such as pancakes, mashed potatoes,
pudding and instant, hot breakfast cereals.
• Blend a fruit smoothie made with low fat or fat free yogurt for a great breakfast.
• Sprinkle grated low fat or fat free cheese on salad, soup or pasta.
• Choose low fat or fat free milk instead of carbonated soft drinks.
• Serve raw fruits and vegetables with a low fat or fat free yogurt based dip.
• Create a vegetable stir-fry and toss in diced calcium-set tofu.
• Enjoy a parfait with fruit and low fat or fat free yogurt.
• Complement your diet with calcium-fortified foods such as certain cereals, orange juice and soy
beverages.
What affects calcium absorption and excretion?
Calcium absorption refers to the amount of calcium that is absorbed from the digestive tract into our
body's circulation. Calcium absorption can be affected by the calcium status of the body, vitamin D
status, age, pregnancy and plant substances in the diet. The amount of calcium consumed at one
time such as in a meal can also affect absorption. For example, the efficiency of calcium absorption
decreases as the amount of calcium consumed at a meal increases.
• Age:
Net calcium absorption can be as high as 60% in infants and young children, when the body needs
calcium to build strong bones [2,11]. Absorption slowly decreases to 15-20% in adulthood and even
more as one ages [2,11,12]. Because calcium absorption declines with age, recommendations for
dietary intake of calcium are higher for adults ages 51 and over.
• Vitamin D:
Vitamin D helps improve calcium absorption. Your body can obtain vitamin D from food and it can
also make vitamin D when your skin is exposed to sunlight. Thus, adequate vitamin D intake from
food and sun exposure is essential to bone health. The Office of Dietary Supplement's vitamin D fact
sheet provides more information: http://ods.od.nih.gov/factsheets/vitamind.asp.
• Pregnancy:
Current calcium recommendations for nonpregnant women are also sufficient for pregnant women
because intestinal calcium absorption increases during pregnancy [2]. For this reason, the calcium
recommendations established for pregnant women are not different than the recommendations for
women who are not pregnant.
• Plant substances:
Phytic acid and oxalic acid, which are found naturally in some plants, may bind to calcium and prevent
it from being absorbed optimally. These substances affect the absorption of calcium from the plant
itself not the calcium found in other calcium-containing foods eaten at the same time [6]. Examples of
foods high in oxalic acid are spinach, collard greens, sweet potatoes, rhubarb, and beans. Foods
high in phytic acid include whole grain bread, beans, seeds, nuts, grains, and soy isolates [2].
Although soybeans are high in phytic acid, the calcium present in soybeans is still partially absorbed
[2,13]. Fiber, particularly from wheat bran, could also prevent calcium absorption because of its
content of phytate. However, the effect of fiber on calcium absorption is more of a concern for
individuals with low calcium intakes. The average American tends to consume much less fiber per
day than the level that would be needed to affect calcium absorption.
Calcium excretion refers to the amount of calcium eliminated from the body in urine, feces and
sweat. Calcium excretion can be affected by many factors including dietary sodium, protein, caffeine
and potassium.
• Sodium and protein:
Typically, dietary sodium and protein increase calcium excretion as the amount of their intake is
increased [5,14]. However, if a high protein, high sodium food also contains calcium, this may help
counteract the loss of calcium.
• Potassium:
Increasing dietary potassium intake (such as from 7-8 servings of fruits and vegetables per day) in
the presence of a high sodium diet (>5100 mg/day, which is more than twice the Tolerable Upper
Intake Level of 2300 mg for sodium per day) may help decrease calcium excretion particularly in
postmenopausal women [15,16].
• Caffeine:
Caffeine has a small effect on calcium absorption. It can temporarily increase calcium excretion and
may modestly decrease calcium absorption, an effect easily offset by increasing calcium
consumption in the diet [17]. One cup of regular brewed coffee causes a loss of only 2-3 mg of
calcium easily offset by adding a tablespoon of milk [14]. Moderate caffeine consumption, (1 cup of
coffee or 2 cups of tea per day), in young women who have adequate calcium intakes has little to no
negative effects on their bones [18].
Other factors:
• Phosphorus: The effect of dietary phosphorus on calcium is minimal. Some researchers
speculate that the detrimental effects of consuming foods high in phosphate such as carbonated
soft drinks is due to the replacement of milk with soda rather than the phosphate level itself [19,20].
• Alcohol: Alcohol can affect calcium status by reducing the intestinal absorption of calcium [21].
It can also inhibit enzymes in the liver that help convert vitamin D to its active form which in turn
reduces calcium absorption [3]. However, the amount of alcohol required to affect calcium
absorption is unknown. Evidence is currently conflicting whether moderate alcohol consumption is
helpful or harmful to bone.
In summary, a variety of factors that may cause a decrease in calcium absorption and/or increase in
calcium excretion may negatively affect bone health.
Calcium's role in health and disease prevention
Calcium and bone health
Your bones are living tissues and continue to change throughout life. During childhood and
adolescence, bones increase in size and mass. Bones continue to add more mass until around age
30, when peak bone mass is reached. Peak bone mass is the point when the maximum amount of
bone is achieved. Because bone loss, like bone growth, is a gradual process, the stronger your
bones are at age 30, the more your bone loss will be delayed as you age. Therefore, it is particularly
important to consume adequate calcium and vitamin D throughout infancy, childhood, and
adolescence. It is also important to engage in weight-bearing exercise to maximize bone strength
and bone density (amount of bone tissue in a certain volume of bone) to help prevent osteoporosis
later in life. Weight bearing exercise is the type of exercise that causes your bones and muscles to
work against gravity while they bear your weight. Resistance exercises such as weight training are
also important because they help to improve muscle mass and bone strength.
Examples of weight bearing exercise
• walking
• running
• dancing
• aerobics
• skating
Examples of NON-weight bearing exercise
• swimming
• bicycling
• water aerobics
Osteoporosis is a disorder characterized by porous, fragile bones. It is a serious public health
problem for more than 10 million Americans, 80% of whom are women. Another 34 million Americans
have osteopenia, or low bone mass, which precedes osteoporosis. Osteoporosis is a concern
because of its association with fractures of the hip, vertebrae, wrist, pelvis, ribs, and other bones
[22]. Each year, Americans suffer from 1.5 million fractures because of osteoporosis [23].
Osteoporosis and osteopenia can result from dietary factors such as [11,24,25]:
• chronically low calcium intake
• low vitamin D intake
• poor calcium absorption
• excess calcium excretion
When calcium intake is low or calcium is poorly absorbed, bone breakdown occurs because the body
must use the calcium stored in bones to maintain normal biological functions such as nerve and
muscle function. Bone loss also occurs as a part of the aging process. A prime example is the loss of
bone mass observed in post-menopausal women because of decreased amounts of the hormone
estrogen. Researchers have identified many factors that increase the risk for developing
osteoporosis. These factors include being female, thin, inactive, of advanced age, cigarette
smoking, excessive intake of alcohol, and having a family history of osteoporosis [26].
In 1993 the FDA authorized a health claim for food labels on calcium and osteoporosis in response to
scientific evidence that an inadequate calcium intake is one factor that can lead to low peak bone
mass and is considered a risk factor for osteoporosis [27]. The claim states that "adequate calcium
intake throughout life is linked to reduced risk of osteoporosis through the mechanism of optimizing
peak bone mass during adolescence and early adulthood and decreasing bone loss later in life".
Various bone mineral density (BMD) tests, including those that measure your hip, spine, wrist, finger,
shin bone, and heel, can help determine bone mass. These tests provide a T-score which is a
measure of bone mineral density that compares an individual's BMD to an optimal BMD of a 30 year
old healthy adult. See Figure 2 below. A T-Score of -1.0 and above indicates normal bone density. A T-
score of -1.0 to -2.5 indicates that a person is considered to have low bone mass (osteopenia). A
score below -2.5 indicates osteoporosis [28].
Although osteoporosis affects people of different races, genders and ethnicities, women are at
highest risk because their skeletons are smaller to start with and because of the accelerated bone
loss that accompanies menopause. Adequate calcium and vitamin D intakes, as well as weight
bearing exercise are critical to the development and maintenance of healthy bone throughout the
lifecycle. Older adults should strive to maintain recommended daily calcium intakes as well as an
adequate vitamin D intake.
Calcium and high blood pressure
Some observational studies (type of research study in which the treatment/intervention is observed
and not controlled by the researchers) and experimental studies (type of research study in which the
researchers control the treatments/interventions and that are assigned to participants) indicate that
individuals who eat a vegetarian diet high in minerals (including calcium, magnesium and potassium)
and fiber, and low in fat, tend to have reduced blood pressure [29-31].
Findings from some clinical trials (a specific type of experimental study) used to evaluate the effects
of one or more treatments/interventions in humans) indicate that an increased calcium intake lowers
blood pressure and the risk of hypertension (high blood pressure) [32,33]. However, the results of
some studies produced small and inconsistent reductions in blood pressure. One reason for these
results is because these research studies tended to test the effect of single nutrients rather than
foods on blood pressure.
To help test the combined effect of nutrients including calcium from food on blood pressure, a study
was conducted to investigate the impact of various dietary eating patterns on blood pressure. This
study titled "Dietary Approaches to Stop Hypertension (DASH)" was reported in 1997 by the National,
Heart, Lung and Blood Institute of the National Institutes of Health. It investigated the effect of
various eating patterns on lowering blood pressure. The DASH study was a multi-center research
trial where food was provided to over 450 adults. It examined the effects of three different diets on
high blood pressure: a control, "typical American" diet and two modified diets (high fruits-and-
vegetables and a combination "DASH" diet - high in fruits, vegetables, and low fat dairy). See Table 3
for a comparison of some of the components of the three diets.
Calcium and cancer
Colorectal cancer
The relationship between calcium intake and the risk of colon cancer has not been conclusively
determined. Observational and experimental research studies investigating the role calcium plays in
the prevention of colon cancer show mixed results. Some studies suggest that increased intakes of
dietary (low fat dairy sources) and supplemental calcium are associated with a decreased risk of
colon cancer [38-41]. Supplementation with calcium carbonate is reported to lead to reduced risk of
adenomas (nonmalignant tumors) in the colon, a precursor to colon cancer, but it is not known if this
will ultimately translate into reduced cancer risk [42]. Another study reported on the association
between diet and colon cancer history in 135,000 men and women participating in two large health
surveys, the Nurses' Health Study and the Physicians' Health Study. The authors found that those
who consumed 700 to 800 mg calcium per day had a 40 to 50% lower risk of developing left side colon
cancer [43]. However, a few other observational studies found inconclusive evidence regarding any
association of calcium intake with colon cancer [44-46]. Although some research findings indicate a
protective effect of calcium or low fat dairy foods against colon cancer, further studies are
necessary to confirm this role for calcium.
Prostate cancer
There is some evidence to suggest that higher calcium (ranging from 600 mg to >2000 mg of calcium)
and/or dairy intakes (>2.5 servings) may be associated with the development of prostate cancer [47-
50]. However, these studies are observational in nature rather than clinical trials and cannot
establish a definite causal relationship between calcium and prostate cancer. Other findings only
show a weak relationship, no relationship at all or the opposite relationship between calcium and
prostate cancer [51-54]. Thus, the relationship between calcium intake, dairy intake and prostate
cancer risk remains unclear. At the present time, it is recommended that men ages 19 and over
consume a "modest" intake of calcium ranging from 1000-1200 mg per day and maintain an intake
below the upper tolerable limit (2500 mg) [1].
Calcium and kidney stones
Kidney stones are crystallized deposits of calcium and other minerals in the urinary tract. Calcium
oxalate stones are the most common form of kidney stones in the US. High calcium intakes or high
calcium absorption were previously thought to contribute to the development of kidney stones.
However, more recent studies show that high dietary calcium intakes actually decrease the risk for
kidney stones [55-57]. Other factors such as high oxalate intake and reduced fluid consumption
appear to be more of a risk factor in the formation of kidney stones than calcium in most individuals
[58].
Calcium and weight management
Several studies, primarily observational in nature, have linked higher calcium intakes to lower body
weights or less weight gain over time [59-62]. Two explanations have been proposed for how calcium
may help to regulate body weight. First, high-calcium intakes may reduce calcium concentrations in
fat cells by lowering the production of two hormones (parathyroid hormone and an active form of
vitamin D), which in turn increases fat breakdown in these cells and discourages its accumulation
[61]. In addition, calcium from food or supplements may bind to small amounts of dietary fat in the
digestive tract and prevent its absorption, carrying the fat (and the calories it would otherwise
provide) out in the feces [61,63].
Dairy products in particular may contain additional components that have even greater effects on
body weight than their calcium content alone would suggest [64-69]. Three small, recently published
clinical trials show that calcium-rich dairy products may help obese individuals following reduced-
calorie diets to lose some excess weight and fat [67-69]. In one trial, 32 obese adults were
randomized to one of three groups: eating a standard diet providing 400-500 mg calcium, eating a
standard diet supplemented with 800 mg calcium, and eating a diet with 3 servings/day of dairy
products to provide 1,200-1,300 mg calcium [67]. The subjects ate 500 fewer calories a day over the
24 weeks of the study. All lost weight and body fat, but those taking the calcium supplements lost
significantly more than subjects eating the unsupplemented standard diet, and those on the high-
dairy diet lost by far the most. Dairy products also favorably affected body composition in a small
group of obese African-American adults who followed a weight-maintenance program for 24 weeks
[69]. Subjects who ate 3 servings/day of dairy products, which increased calcium intakes to 1,200
mg/day, lost significantly more fat (both total body and abdominal) and preserved lean body mass as
compared to those who consumed less than one daily serving of these foods and 500 mg/day total
calcium.
Despite the hopeful results of these studies, other recent clinical trials make it clear that the
involvement of calcium and dairy products in weight regulation and body composition is complex,
inconsistent, and not well understood [61,70]. For example, one study in young women of normal
body weight found that higher intakes of dairy products had no effect on weight or fat mass over the
course of one year [71]. Another study in which 100 overweight and obese pre- and post-menopausal
women on reduced-calorie diets received either 1,000 mg/day calcium or a placebo for 25 weeks
found no significant differences in weight or fat loss between the groups [72]. Similar results were
obtained in a study of 1,471 postmenopausal women (somewhat overweight on average) who were
randomly assigned to take 1,000 mg/day calcium or a placebo for 30 months, though there was a
trend toward greater weight loss in those who took the calcium supplement and whose calcium
intakes from food averaged less than 600 mg/day [73]. Clearly, larger clinical trials are needed to
better assess the effects of calcium and dairy products on body weight, composition, and fat
distribution [61,74].
than 99% of total body calcium is stored in the bones and teeth where it functions to support their
structure [1]. The remaining 1% is found throughout the body in blood, muscle, and the fluid between
cells. Calcium is needed for muscle contraction, blood vessel contraction and expansion, the
secretion of hormones and enzymes, and sending messages through the nervous system [2]. A
constant level of calcium is maintained in body fluid and tissues so that these vital body processes
function efficiently.
Bone undergoes continuous remodeling, with constant resorption (breakdown of bone) and
deposition of calcium into newly deposited bone (bone formation) [2]. The balance between bone
resorption and deposition changes as people age. During childhood there is a higher amount of
bone formation and less breakdown. In early and middle adulthood, these processes are relatively
equal. In aging adults, particularly among postmenopausal women, bone breakdown exceeds its
formation, resulting in bone loss, which increases the risk for osteoporosis (a disorder characterized
by porous, weak bones) [2].
What is the recommended intake for calcium?
Recommendations for calcium are provided in the Dietary Reference Intakes (DRIs) developed by the
Institute of Medicine (IOM) of the National Academy of Sciences. Dietary Reference Intake (DRI) is the
general term for a set of reference values used for planning and assessing nutrient intakes of
healthy people. Three important types of reference values included in the DRIs are Recommended
Dietary Allowances (RDA), Adequate Intakes (AI), and Tolerable Upper Intake Levels (UL). The RDA
recommends the average daily intake that is sufficient to meet the nutrient requirements of nearly all
(97-98%) healthy individuals in each age and gender group. An AI is set when there is insufficient
scientific data available to establish a RDA. AIs meet or exceed the amount needed to maintain a
nutritional state of adequacy in nearly all members of a specific age and gender group. The UL, on
the other hand, is the maximum daily intake unlikely to result in adverse effects. It is listed in the
section "Is there health risk of too much calcium?" of this fact sheet.
For calcium, the recommended intake is listed as an Adequate Intake (AI), which is a recommended
average intake level based on observed or experimentally determined levels.
• What foods provide calcium?
In the United States (U.S.), milk, yogurt and cheese are the major contributors of calcium in the
typical diet [4]. The inadequate intake of dairy foods may explain why some Americans are deficient in
calcium since dairy foods are the major source of calcium in the diet [4]. The U.S. Department of
Agriculture's Food Guide Pyramid recommends that individuals two years and older eat 2-3 servings
of dairy products per day. A serving is equal to:
• 1 cup (8 fl oz) of milk
• 8 oz of yogurt
• 1.5 oz of natural cheese (such as Cheddar)
• 2.0 oz of processed cheese (such as American)
A variety of non-fat and reduced fat dairy products that contain the same amount of calcium as
regular dairy products are available in the U.S. today for individuals concerned about saturated fat
content from regular dairy products.
Although dairy products are the main source of calcium in the U.S. diet, other foods also contribute
to overall calcium intake. Individuals with lactose intolerance (those who experience symptoms such
as bloating and diarrhea because they cannot completely digest the milk sugar lactose) and those
who are vegan (people who consume no animal products) tend to avoid or completely eliminate dairy
products from their diets [2]. Thus, it is important for these individuals to meet their calcium needs
with alternative calcium sources if they choose to avoid or eliminate dairy products from their diet.
Foods such as Chinese cabbage, kale and broccoli are other alternative calcium sources [2].
Although most grains are not high in calcium (unless fortified), they do contribute calcium to the diet
because they are consumed frequently [2]. Additionally, there are several calcium-fortified food
sources presently available, including fruit juices, fruit drinks, tofu and cereals. Figure 1 compares
portion sizes of various foods that provide the amount of calcium in one cup of milk. This figure
takes into account that calcium absorption varies among foods. Certain plant-based foods such as
some vegetables contain substances which can reduce calcium absorption. Thus, you may have to
eat several servings of certain foods such as spinach to obtain the same amount of calcium in one
cup of milk, which is not only calcium-rich but also contains calcium in an easily absorbable form.
Table 2 contains additional listings of food sources of calcium.
• Helping hints for meeting your calcium needs
As the 2000 Dietary Guidelines for Americans states, "Different foods contain different nutrients and
other healthful substances. No single food can supply all the nutrients in the amounts you need" [9].
For more information about building a healthful diet, refer to the Dietary Guidelines for Americans
http://www.usda.gov/cnpp/DietGd.pdf and the US Department of Agriculture's Food Guide Pyramid
http://www.nal.usda.gov/fnic/Fpyr/pyramid.html [9,10].
The following are strategies and tips to help you meet your calcium needs each day:
• Use low fat or fat free milk instead of water in recipes such as pancakes, mashed potatoes,
pudding and instant, hot breakfast cereals.
• Blend a fruit smoothie made with low fat or fat free yogurt for a great breakfast.
• Sprinkle grated low fat or fat free cheese on salad, soup or pasta.
• Choose low fat or fat free milk instead of carbonated soft drinks.
• Serve raw fruits and vegetables with a low fat or fat free yogurt based dip.
• Create a vegetable stir-fry and toss in diced calcium-set tofu.
• Enjoy a parfait with fruit and low fat or fat free yogurt.
• Complement your diet with calcium-fortified foods such as certain cereals, orange juice and soy
beverages.
What affects calcium absorption and excretion?
Calcium absorption refers to the amount of calcium that is absorbed from the digestive tract into our
body's circulation. Calcium absorption can be affected by the calcium status of the body, vitamin D
status, age, pregnancy and plant substances in the diet. The amount of calcium consumed at one
time such as in a meal can also affect absorption. For example, the efficiency of calcium absorption
decreases as the amount of calcium consumed at a meal increases.
• Age:
Net calcium absorption can be as high as 60% in infants and young children, when the body needs
calcium to build strong bones [2,11]. Absorption slowly decreases to 15-20% in adulthood and even
more as one ages [2,11,12]. Because calcium absorption declines with age, recommendations for
dietary intake of calcium are higher for adults ages 51 and over.
• Vitamin D:
Vitamin D helps improve calcium absorption. Your body can obtain vitamin D from food and it can
also make vitamin D when your skin is exposed to sunlight. Thus, adequate vitamin D intake from
food and sun exposure is essential to bone health. The Office of Dietary Supplement's vitamin D fact
sheet provides more information: http://ods.od.nih.gov/factsheets/vitamind.asp.
• Pregnancy:
Current calcium recommendations for nonpregnant women are also sufficient for pregnant women
because intestinal calcium absorption increases during pregnancy [2]. For this reason, the calcium
recommendations established for pregnant women are not different than the recommendations for
women who are not pregnant.
• Plant substances:
Phytic acid and oxalic acid, which are found naturally in some plants, may bind to calcium and prevent
it from being absorbed optimally. These substances affect the absorption of calcium from the plant
itself not the calcium found in other calcium-containing foods eaten at the same time [6]. Examples of
foods high in oxalic acid are spinach, collard greens, sweet potatoes, rhubarb, and beans. Foods
high in phytic acid include whole grain bread, beans, seeds, nuts, grains, and soy isolates [2].
Although soybeans are high in phytic acid, the calcium present in soybeans is still partially absorbed
[2,13]. Fiber, particularly from wheat bran, could also prevent calcium absorption because of its
content of phytate. However, the effect of fiber on calcium absorption is more of a concern for
individuals with low calcium intakes. The average American tends to consume much less fiber per
day than the level that would be needed to affect calcium absorption.
Calcium excretion refers to the amount of calcium eliminated from the body in urine, feces and
sweat. Calcium excretion can be affected by many factors including dietary sodium, protein, caffeine
and potassium.
• Sodium and protein:
Typically, dietary sodium and protein increase calcium excretion as the amount of their intake is
increased [5,14]. However, if a high protein, high sodium food also contains calcium, this may help
counteract the loss of calcium.
• Potassium:
Increasing dietary potassium intake (such as from 7-8 servings of fruits and vegetables per day) in
the presence of a high sodium diet (>5100 mg/day, which is more than twice the Tolerable Upper
Intake Level of 2300 mg for sodium per day) may help decrease calcium excretion particularly in
postmenopausal women [15,16].
• Caffeine:
Caffeine has a small effect on calcium absorption. It can temporarily increase calcium excretion and
may modestly decrease calcium absorption, an effect easily offset by increasing calcium
consumption in the diet [17]. One cup of regular brewed coffee causes a loss of only 2-3 mg of
calcium easily offset by adding a tablespoon of milk [14]. Moderate caffeine consumption, (1 cup of
coffee or 2 cups of tea per day), in young women who have adequate calcium intakes has little to no
negative effects on their bones [18].
Other factors:
• Phosphorus: The effect of dietary phosphorus on calcium is minimal. Some researchers
speculate that the detrimental effects of consuming foods high in phosphate such as carbonated
soft drinks is due to the replacement of milk with soda rather than the phosphate level itself [19,20].
• Alcohol: Alcohol can affect calcium status by reducing the intestinal absorption of calcium [21].
It can also inhibit enzymes in the liver that help convert vitamin D to its active form which in turn
reduces calcium absorption [3]. However, the amount of alcohol required to affect calcium
absorption is unknown. Evidence is currently conflicting whether moderate alcohol consumption is
helpful or harmful to bone.
In summary, a variety of factors that may cause a decrease in calcium absorption and/or increase in
calcium excretion may negatively affect bone health.
Calcium's role in health and disease prevention
Calcium and bone health
Your bones are living tissues and continue to change throughout life. During childhood and
adolescence, bones increase in size and mass. Bones continue to add more mass until around age
30, when peak bone mass is reached. Peak bone mass is the point when the maximum amount of
bone is achieved. Because bone loss, like bone growth, is a gradual process, the stronger your
bones are at age 30, the more your bone loss will be delayed as you age. Therefore, it is particularly
important to consume adequate calcium and vitamin D throughout infancy, childhood, and
adolescence. It is also important to engage in weight-bearing exercise to maximize bone strength
and bone density (amount of bone tissue in a certain volume of bone) to help prevent osteoporosis
later in life. Weight bearing exercise is the type of exercise that causes your bones and muscles to
work against gravity while they bear your weight. Resistance exercises such as weight training are
also important because they help to improve muscle mass and bone strength.
Examples of weight bearing exercise
• walking
• running
• dancing
• aerobics
• skating
Examples of NON-weight bearing exercise
• swimming
• bicycling
• water aerobics
Osteoporosis is a disorder characterized by porous, fragile bones. It is a serious public health
problem for more than 10 million Americans, 80% of whom are women. Another 34 million Americans
have osteopenia, or low bone mass, which precedes osteoporosis. Osteoporosis is a concern
because of its association with fractures of the hip, vertebrae, wrist, pelvis, ribs, and other bones
[22]. Each year, Americans suffer from 1.5 million fractures because of osteoporosis [23].
Osteoporosis and osteopenia can result from dietary factors such as [11,24,25]:
• chronically low calcium intake
• low vitamin D intake
• poor calcium absorption
• excess calcium excretion
When calcium intake is low or calcium is poorly absorbed, bone breakdown occurs because the body
must use the calcium stored in bones to maintain normal biological functions such as nerve and
muscle function. Bone loss also occurs as a part of the aging process. A prime example is the loss of
bone mass observed in post-menopausal women because of decreased amounts of the hormone
estrogen. Researchers have identified many factors that increase the risk for developing
osteoporosis. These factors include being female, thin, inactive, of advanced age, cigarette
smoking, excessive intake of alcohol, and having a family history of osteoporosis [26].
In 1993 the FDA authorized a health claim for food labels on calcium and osteoporosis in response to
scientific evidence that an inadequate calcium intake is one factor that can lead to low peak bone
mass and is considered a risk factor for osteoporosis [27]. The claim states that "adequate calcium
intake throughout life is linked to reduced risk of osteoporosis through the mechanism of optimizing
peak bone mass during adolescence and early adulthood and decreasing bone loss later in life".
Various bone mineral density (BMD) tests, including those that measure your hip, spine, wrist, finger,
shin bone, and heel, can help determine bone mass. These tests provide a T-score which is a
measure of bone mineral density that compares an individual's BMD to an optimal BMD of a 30 year
old healthy adult. See Figure 2 below. A T-Score of -1.0 and above indicates normal bone density. A T-
score of -1.0 to -2.5 indicates that a person is considered to have low bone mass (osteopenia). A
score below -2.5 indicates osteoporosis [28].
Although osteoporosis affects people of different races, genders and ethnicities, women are at
highest risk because their skeletons are smaller to start with and because of the accelerated bone
loss that accompanies menopause. Adequate calcium and vitamin D intakes, as well as weight
bearing exercise are critical to the development and maintenance of healthy bone throughout the
lifecycle. Older adults should strive to maintain recommended daily calcium intakes as well as an
adequate vitamin D intake.
Calcium and high blood pressure
Some observational studies (type of research study in which the treatment/intervention is observed
and not controlled by the researchers) and experimental studies (type of research study in which the
researchers control the treatments/interventions and that are assigned to participants) indicate that
individuals who eat a vegetarian diet high in minerals (including calcium, magnesium and potassium)
and fiber, and low in fat, tend to have reduced blood pressure [29-31].
Findings from some clinical trials (a specific type of experimental study) used to evaluate the effects
of one or more treatments/interventions in humans) indicate that an increased calcium intake lowers
blood pressure and the risk of hypertension (high blood pressure) [32,33]. However, the results of
some studies produced small and inconsistent reductions in blood pressure. One reason for these
results is because these research studies tended to test the effect of single nutrients rather than
foods on blood pressure.
To help test the combined effect of nutrients including calcium from food on blood pressure, a study
was conducted to investigate the impact of various dietary eating patterns on blood pressure. This
study titled "Dietary Approaches to Stop Hypertension (DASH)" was reported in 1997 by the National,
Heart, Lung and Blood Institute of the National Institutes of Health. It investigated the effect of
various eating patterns on lowering blood pressure. The DASH study was a multi-center research
trial where food was provided to over 450 adults. It examined the effects of three different diets on
high blood pressure: a control, "typical American" diet and two modified diets (high fruits-and-
vegetables and a combination "DASH" diet - high in fruits, vegetables, and low fat dairy). See Table 3
for a comparison of some of the components of the three diets.
Calcium and cancer
Colorectal cancer
The relationship between calcium intake and the risk of colon cancer has not been conclusively
determined. Observational and experimental research studies investigating the role calcium plays in
the prevention of colon cancer show mixed results. Some studies suggest that increased intakes of
dietary (low fat dairy sources) and supplemental calcium are associated with a decreased risk of
colon cancer [38-41]. Supplementation with calcium carbonate is reported to lead to reduced risk of
adenomas (nonmalignant tumors) in the colon, a precursor to colon cancer, but it is not known if this
will ultimately translate into reduced cancer risk [42]. Another study reported on the association
between diet and colon cancer history in 135,000 men and women participating in two large health
surveys, the Nurses' Health Study and the Physicians' Health Study. The authors found that those
who consumed 700 to 800 mg calcium per day had a 40 to 50% lower risk of developing left side colon
cancer [43]. However, a few other observational studies found inconclusive evidence regarding any
association of calcium intake with colon cancer [44-46]. Although some research findings indicate a
protective effect of calcium or low fat dairy foods against colon cancer, further studies are
necessary to confirm this role for calcium.
Prostate cancer
There is some evidence to suggest that higher calcium (ranging from 600 mg to >2000 mg of calcium)
and/or dairy intakes (>2.5 servings) may be associated with the development of prostate cancer [47-
50]. However, these studies are observational in nature rather than clinical trials and cannot
establish a definite causal relationship between calcium and prostate cancer. Other findings only
show a weak relationship, no relationship at all or the opposite relationship between calcium and
prostate cancer [51-54]. Thus, the relationship between calcium intake, dairy intake and prostate
cancer risk remains unclear. At the present time, it is recommended that men ages 19 and over
consume a "modest" intake of calcium ranging from 1000-1200 mg per day and maintain an intake
below the upper tolerable limit (2500 mg) [1].
Calcium and kidney stones
Kidney stones are crystallized deposits of calcium and other minerals in the urinary tract. Calcium
oxalate stones are the most common form of kidney stones in the US. High calcium intakes or high
calcium absorption were previously thought to contribute to the development of kidney stones.
However, more recent studies show that high dietary calcium intakes actually decrease the risk for
kidney stones [55-57]. Other factors such as high oxalate intake and reduced fluid consumption
appear to be more of a risk factor in the formation of kidney stones than calcium in most individuals
[58].
Calcium and weight management
Several studies, primarily observational in nature, have linked higher calcium intakes to lower body
weights or less weight gain over time [59-62]. Two explanations have been proposed for how calcium
may help to regulate body weight. First, high-calcium intakes may reduce calcium concentrations in
fat cells by lowering the production of two hormones (parathyroid hormone and an active form of
vitamin D), which in turn increases fat breakdown in these cells and discourages its accumulation
[61]. In addition, calcium from food or supplements may bind to small amounts of dietary fat in the
digestive tract and prevent its absorption, carrying the fat (and the calories it would otherwise
provide) out in the feces [61,63].
Dairy products in particular may contain additional components that have even greater effects on
body weight than their calcium content alone would suggest [64-69]. Three small, recently published
clinical trials show that calcium-rich dairy products may help obese individuals following reduced-
calorie diets to lose some excess weight and fat [67-69]. In one trial, 32 obese adults were
randomized to one of three groups: eating a standard diet providing 400-500 mg calcium, eating a
standard diet supplemented with 800 mg calcium, and eating a diet with 3 servings/day of dairy
products to provide 1,200-1,300 mg calcium [67]. The subjects ate 500 fewer calories a day over the
24 weeks of the study. All lost weight and body fat, but those taking the calcium supplements lost
significantly more than subjects eating the unsupplemented standard diet, and those on the high-
dairy diet lost by far the most. Dairy products also favorably affected body composition in a small
group of obese African-American adults who followed a weight-maintenance program for 24 weeks
[69]. Subjects who ate 3 servings/day of dairy products, which increased calcium intakes to 1,200
mg/day, lost significantly more fat (both total body and abdominal) and preserved lean body mass as
compared to those who consumed less than one daily serving of these foods and 500 mg/day total
calcium.
Despite the hopeful results of these studies, other recent clinical trials make it clear that the
involvement of calcium and dairy products in weight regulation and body composition is complex,
inconsistent, and not well understood [61,70]. For example, one study in young women of normal
body weight found that higher intakes of dairy products had no effect on weight or fat mass over the
course of one year [71]. Another study in which 100 overweight and obese pre- and post-menopausal
women on reduced-calorie diets received either 1,000 mg/day calcium or a placebo for 25 weeks
found no significant differences in weight or fat loss between the groups [72]. Similar results were
obtained in a study of 1,471 postmenopausal women (somewhat overweight on average) who were
randomly assigned to take 1,000 mg/day calcium or a placebo for 30 months, though there was a
trend toward greater weight loss in those who took the calcium supplement and whose calcium
intakes from food averaged less than 600 mg/day [73]. Clearly, larger clinical trials are needed to
better assess the effects of calcium and dairy products on body weight, composition, and fat
distribution [61,74].