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12.2B: Calcium Bioavailability

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    1557
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    Calcium bioavailability varies greatly from food to food, as shown in the table below. This table gives the serving size, calcium content of that food, and percent absorbed. The calcium content is multiplied by the absorption percentage to calculate the estimated calcium absorbed. Finally, it shows the servings of each food needed to equal the estimated calcium absorbed from 1 serving of milk.

    Table 12.221 Bioavailability of calcium from different foods sources1-3

    Food

    Serving Size (g)

    Calcium content (mg)

    Absorption (%)

    Estimated Calcium Absorbed

    Servings needed to equal 240 mL milk

    Cow’s Milk

    240

    300

    32.1

    96.3

    1.0

    Almonds, dry roasted

    28

    80

    21.2

    17.0

    5.7

    Beans, Pinto

    86

    44.7

    26.7

    11.9

    8.1

    Beans, Red

    172

    40.5

    24.4

    9.9

    9.7

    Beans, White

    110

    113

    21.8

    24.7

    3.9

    Bok Choy

    85

    79

    53.8

    42.5

    2.3

    Broccoli

    71

    35

    61.3

    21.5

    4.5

    Brussel Sprouts

    78

    19

    63.8

    12.1

    8.0

    Cabbage, Chinese

    85

    79

    53.8

    42.5

    2.3

    Cabbage, Green

    75

    25

    64.9

    16.2

    5.9

    Cauliflower

    62

    17

    68.6

    11.7

    8.2

    Cheddar Cheese

    42

    303

    32.1

    97.2

    1.0

    Chinese mustard greens

    85

    212

    40.2

    85.3

    1.1

    Chinese spinach

    85

    347

    8.36

    29

    3.3

    Fruit Punch  (CCM)

    240

    300

    52

    156

    0.6

    Kale

    85

    61

    49.3

    30.1

    3.2

    Kohlrabi

    82

    20

    67.0

    13.4

    7.2

    Mustard Greens

    72

    64

    57.8

    37.0

    2.6

    Orange juice (CCM)

    240

    300

    36.3

    109

    0.8

    Radish

    50

    14

    74.4

    10.4

    9.2

    Rhubarb

    120

    174

    8.54

    10.1

    9.5

    Rutabaga

    85

    36

    61.4

    22.1

    4.4

    Sesame seeds, no hulls

    28

    37

    20.8

    7.7

    12.2

    Soy milk (tricalcium phosphate)

    240

    300

    24.0

    72.0

    1.3

    Soy milk (calcium carbonate)

    240

    300

    21.1

    66.3

    1.0

    Spinach

    85

    115

    5.1

    5.9

    16.3

    Sweet Potatoes

    164

    44

    22.2

    9.8

    9.8

    Tofu with Ca

    126

    258

    31.0

    80.0

    1.2

    Turnip Greens

    72

    99

    51.6

    51.1

    1.9

    Watercress

    17

    20

    67.0

    13.4

    7.2

    Yogurt

    240

    300

    32.1

    96.3

    1.0

    Notice that the foods high in oxalates like spinach, rhubarb, sweet potatoes, and dried beans are poorly absorbed. But there are still a number of calcium sources outside of milk. 

    The 2 most common forms of calcium found in supplements are calcium carbonate and calcium citrate. As you can see in the figure below, they differ in the amount of elemental calcium they contain. This shows how much of the molecular weight of the compound is calcium.

    Figure 12.221 Percent of calcium supplements that is elemental calcium4

    The higher the percent elemental calcium, the greater the amount of calcium you will receive per given weight of that compound, versus a compound that has a lower elemental calcium percentage. Both carbonate and citrate forms are well absorbed, but individuals with low stomach acid absorb citrate better. Also, carbonate is best absorbed when taken with food, while for citrate it is equally well absorbed when taken alone4.

    Older research suggested that calcium citrate malate was more bioavailable than other calcium sources. However, a more recent clinical study found no difference in the bioavailability of calcium from calcium citrate malate in orange juice, skim milk, or calcium carbonate supplements5. There is some evidence that suggests that even though bioavailability is the same among these different forms, they might not be equally effective in improving bone measures6.

    References & Links

    1. Weaver CM, Plawecki KL. (1994) Dietary calcium: Adequacy of a vegetarian diet. Am J Clin Nutr 59(5 Suppl): 1238S-1241S.
    2. Weaver CM, Proulx WR, Heaney R. (1999) Choices for achieving adequate dietary calcium with a vegetarian diet. Am J Clin Nutr 70(3 Suppl): 543S-548S.
    3. Weaver C. (2009) Closing the gap between calcium intake and requirements. J Am Diet Assoc 109(5): 812-813.
    4. ttp://www.ahs6.com/liquidcalcium/absorb.php
    5. Martini L, Wood R. (2002) Relative bioavailability of calcium-rich dietary sources in the elderly. Am J Clin Nutr 76(6): 1345-1350.
    6. Weaver C, Janle E, Martin B, Browne S, Guiden H, et al. (2009) Dairy versus calcium carbonate in promoting peak bone mass and bone maintenance during subsequent calcium deficiency. Journal of Bone and Mineral Research 24(8): 1411-1419.