Calcium plays a major role in maintaining skeletal integrity, regulating nerve excitability, muscle contraction, blood coagulation (1) and may help in the prevention of hypertension. A recent study examined the association between calcium intake and colon cancer risk, and concluded that higher calcium intakes are associated with a reduced risk of distal colon cancer, but not proximal colon cancer (2). At this time, more research is needed to support these findings.
Dietary Reference Intakes (DRIs), released by the Food and Nutrition Board of the Institute of Medicine, National Academy of Sciences, are reference values that are quantitative estimates of nutrient intakes to be used for planning and assessing diets for healthy Americans and Canadians (3). Table 1 lists the DRIs for individual intakes for calcium and vitamin D during various life-stages.
|
Table
1. Food and Nutrition Board, Institute of
Medicine-National Academy of Sciences-Dietary Reference Intakes:
Recommended levels for individual intake. |
||
Life-stage
group
|
Calcium
(mg/d) |
Vitamin
D (μg/d)ab |
Infants
|
|
|
|
0-6
mo |
210 |
5 |
|
7-12
mo
|
270 |
5 |
Children
|
|
|
|
1-3
y |
500 |
5 |
|
4-8
y
|
800 |
5 |
Males
|
|
|
|
9-13
y |
1,300 |
5 |
|
14-18
y |
1,300 |
5 |
|
19-30
y |
1,000 |
5 |
|
31-50
y |
1,000 |
5 |
|
51-70
y |
1,200 |
10 |
|
>70
y
|
1,200 |
15 |
Female
|
|
|
|
9-13
y |
1,300 |
5 |
|
14-18
y |
1,300 |
5 |
|
19-30
y |
1,000 |
5 |
|
31-50
y |
1,000 |
5 |
|
51-70
y |
1,200 |
10 |
|
>70
y
|
1,200 |
10 |
Pregnancy
|
|
|
|
≤18
y |
1,300 |
5 |
|
19-30
y |
1,000 |
5 |
|
31-50
y
|
1,000 |
5 |
Lactation
|
|
|
|
≤18
y |
1,300 |
5 |
|
19-30
y |
1,000 |
5 |
|
31-50
y
|
1,000 |
5 |
a As cholecalciferol. 1 μg cholecalciferol=40 IU Vitamin D. b In the absence of adequate exposure to sunlight.
Surveys of the food habits of Americans clearly show that the majority of people do not ingest sufficient quantities of calcium during most of their lives (1).
When assessing calcium
intake for a patient, be sure to assess the patient’s vitamin D status as
well. Total
intake (including diet, supplementation and vitamin D from sunlight) should
remain within the DRI levels. The Tolerable Upper Intake Levels
[1]
for calcium is 2.5 grams/day, and for vitamin D, 50 micrograms/day
for persons over the age of one year.
[1] Tolerable Upper Intake Level (UL) is the highest level of daily nutrient intake that is likely to pose no risks of adverse health effects to almost all individuals in the general population. As intake increases above the UL, the risk of adverse effects increase (2).
Most dairy products are considered to be high-calcium foods. Other foods that are good sources of calcium include dark leafy greens, tofu, almonds and bones found in soft, cooked bony fish. Some common food sources of calcium are listed in Table 2. High amounts of oxalic acid found in certain foods (i.e. beet greens, rhubarb, spinach, peanuts, etc.) can impair absorption by forming insoluble complexes with calcium. Similarly, the outer husks of cereal grains known to contain phytic acid can also form insoluble complexes with calcium. These complexes may remain unabsorbed in the intestine for subsequent excretion in fecal matter.
Table 2. Food Sources of Calcium
| Food | Calcium (milligrams) |
| Total cereal (3/4 cup) | 1,000 |
| Dreyer's or Edy's Frozen Yogurt, calcium fortified (1 cup) | 600 |
| Milk, calcium fortified (1 cup) | 500 |
| Yogurt, fat-free or low-fat, plain (1 cup) | 350-400 |
| Orange Juice with calcium (1 cup) | 350 |
| Quaker Nutrition for Women Instant Oatmeal ( 1 packet) | 350 |
| Milk, fat-free or 1% (1 cup) | 300-350 |
| Swiss cheese (1 oz.) | 270 |
| Yogurt, low-fat, fruit flavored (8 oz.) | 250-350 |
| Sardines canned in water, drained (2 oz.) | 220 |
| Cheddar cheese (1 oz.) | 210 |
| Soy milk, enriched (1 cup) | 200-400 |
| Light n' Lively Twice the Calcium Cottage Cheese (1/2 cup) | 200 |
| Wheatena (1/3 cup dry) | 200 |
| Collard greens, frozen (1/2 cup cooked) | 180 |
| White beans, soybeans, black-eyed peas (1 cup cooked) | 160-210 |
| Ice-cream or frozen yogurt, fat-free or low-fat (1 cup) | 150-300 |
| Ricotta cheese, fat free or light (1/4 cup) | 100-320 |
| Eggo Waffles (2) | 100 |
| Salmon, canned, eaten with the bones (1/4 cup) | 100 |
| Kale, frozen (1/2 cup cooked) | 90 |
| Bok choy (1/2 cup cooked) | 80 |
| Cottage cheese, low-fat (1/2 c p) | 70 |
| Parmesan cheese, grated (1Tbs.) | 70 |
| Black beans, chickpeas, kidneys, pintos (1 cup cooked) | 50-80 |
| Bread, white or whole wheat (2 slices) | 50 |
| Orange (1) | 50 |
| Tofu (3 oz.) | 40-250 |
| Broccoli (1/2 cup cooked) | 40 |
| Soy milk (1 cup) | 20-80 |
Adapted from : Nutrition Action - Health Letter (January/February 2002, Volume 29/ Number 1)
Food manufacturers are
fortifying some popular foods (commonly consumed by population groups) with
calcium, making even more calcium-rich food options available.
A serving of calcium fortified orange juice, ice cream, instant hot
cocoa, or cereal can provide about as much calcium as a glass of milk, which
is typically between one-third and one-fourth of our daily recommended intake.
Be aware that certain dairy products (ie. yogurt, icecream, etc.) may
contain substantially more or less calcium than a similar item processed by a
different manufacturer.
The best way to determine calcium content of a packaged food is by
reading the label.
There are hundreds of calcium formulations commercially
available in the form of supplements. The
most widely studied and commercially available calcium preparations contain
either calcium carbonate, citrate or phosphate.
Calcium
carbonate is a very common supplement. These preparations have the highest
concentration of calcium by weight-typically between 28-40% and are usually
low cost, making it a good choice for many patients. However, calcium
carbonate is a relatively insoluble form of calcium, especially at a
neutral pH and may be absorbed less well in achlorhydric patients. Side effects of large doses
may include constipation and bloating (1).
Calcium
citrate is also a very popular supplement.
These preparations may have a lower calcium content by weight, but are
considered much more soluble than calcium carbonate. Calcium citrate can be
more costly than carbonate, and may be most useful in achlorhydric patients or
those at high risk for kidney stones (1).
Calcium
phosphate preparations tend to be insoluble and they contain considerable
amounts of phosphate, which limits their use in patients with chronic renal
failure. This
preparation is more commonly used in Europe and seems to have comparable
absorbability (1) to citrate and carbonate preparations.
Table 3 compares the amount of elemental calcium per dose for various preparations available in the United States.
Table
3. Dose Comparison of Various Calcium
Preparations
|
|
Elemental
Calcium (mg per dose based on label ) |
Calcium
carbonate
|
|
|
Generic-chewable (Health Vitamin) |
500 |
|
Nephro-calci (R&D Laboratories) |
600 |
|
Tums EX (SmithKline Beecham) |
300 |
|
Calci-chew (R&D Laboratories) |
500 |
|
Tums (SmithKline Beecham) |
200 |
|
Caltrate 600 (Lederle) |
600 |
|
Os-Cal 500 (SmithKline Beecham) |
500 |
|
Viactive Soft Calcium Chew |
500 |
Calcium
citrate
|
|
|
Citracal-liquitab (Mission) |
500 |
|
Citracal (Mission) |
200 |
|
Generic (Freeda) |
250 |
Adapted
from Table 1 of A Review of Calcium Preparations (1).
Calcium absorption may
be enhanced by taking supplements in divided doses with no more than 400-500mg
at a time, taking supplements with a meal, and avoiding coingestion of large
quantities of oxalate, phytate and other substances which may interfere with
absorption.
Calcium
and Nephrolithiasis
The
hypothesis that a high calcium intake increases the risk of calcium oxalate
kidney stones is based largely on the finding (Pak, CYC, 1987) that 20 to 40
percent of patients with recurrent stones have hypercalciuria (4). To
address further the association between intake of calcium and the incidence of
kidney stones, a more recent study by Curhan et al. examined a prospective
cohort of
45,619 men, 40 to 75 years of age, with no history of nephrolithiasis.
The mean (± SD) daily dietary calcium intake was significantly lower
among the men in whom kidney stones later developed than among those who
remained free of stones (797±280 vs. 851 ±307 mg, P<0.001). After
adjustment for age and energy intake, a higher intake of dietary calcium was
strongly associated with a reduced risk of kidney stones (P for trend,
<0.001). The
relative risk for men in the highest as compared with the lowest quintile
group was 0.56 (95 percent confidence interval, 0.43 to 0.73; P<0.001).
Adjustment for age, profession, thiazide use, and intake of animal protein,
potassium, alcohol, and fluid slightly attenuated the apparent protective
effect of dietary calcium, but it remained significant (0.66; 95 percent
confidence interval, 0.49 to 0.90). Overall, the findings from the study
provide no support for the belief that a diet low in calcium reduces the risk
of kidney stones.
In contrast, they suggest that a higher dietary calcium intake may
decrease the incidence of symptomatic kidney stones (5).
For patients predisposed to developing kidney stones containing calcium oxalate, calcium citrate may be the preferred preparation for supplementation (1), and more extensive examination of urine profiles may be indicated. Calcium supplementation may be contraindicated if it impedes absorption of concurrent drug administration.
References:
1. Levenson, D, Bockman, R. A Review of Calcium Preparations. Nutrition Reviews 1994;52(7):221-232.
2. Wu, K, Willett, WC, Fuchs, CS, Colditz, GA, Giovannucci, EL.
Calcium intake and risk of colon cancer in women and men. J Natl Cancer
Inst. 2002, 94(6):437-46.
3. Yates, A, Schlicker, S, Suitor, C. Dietary Reference Intakes: The new basis for recommendations for calcium and related nutrients, B vitamins, and choline. J Am Diet Assoc. 1998;98:699-706.
4. Pak CYC. Medical management of nephrolithiasis in Dallas: update 1987. J Urol. 1988;140:461-467.
5. Curhan, GC, Willett, WC, Rimm, EB, Stampfer, MJ.
A prospective study of dietary calcium and other nutrients and the risk of
symptomatic kidney stones. NEJM. 1993;328(12):833-838.