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12.22: Calcium Bioavailability

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. http://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.