# 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.