12.2B: 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. 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.