Calcium in the Vegan Diet
By Reed Mangles, Ph.D., R.D
The Vegetarian Resource Group
Calcium, needed for strong bones, is found in dark green leafy vegetables, tofu made with calcium sulfate, calcium-fortified soy milk and orange juice, and many other foods commonly eaten by vegans. Although lower animal protein intake may reduce calcium losses, there is currently not enough evidence to suggest that vegans have lower calcium needs. Vegans should eat foods that are high in calcium and/or use a calcium supplement.
The Need for Calcium
Calcium is a very important mineral for humans. Our bones contain large amounts of calcium, which helps to make them firm and rigid. Calcium is also needed for many other tasks including nerve and muscle function and blood clotting. These other tasks are so important for survival, that, when dietary calcium is too low, calcium will be lost from bone and used for other critical functions. The body tightly controls calcium in the blood, so measuring blood calcium levels cannot assess calcium status.
Tofu and Other Sources of Calcium
Because of heavy promotion by the American dairy industry, the public often believes that cow's milk is the sole source of calcium. However, other excellent sources of calcium exist so that vegans eating varied diets that contain these foods need not be concerned about getting adequate calcium.
Sources of well-absorbed calcium for vegans include calcium-fortified soy milk and juice, calcium-set tofu, soybeans and soynuts, bok choy, broccoli, collards, Chinese cabbage, kale, mustard greens, and okra 1. Grains, beans (other than soybeans), fruits, and vegetables (other than those listed) can contribute to calcium intake but cannot replace these key foods.
Table 1 shows the amount of calcium in selected foods. When you realize that there is as much or more calcium in 4 ounces of firm tofu or 3/4 cup of collard greens as there is in one cup of cow's milk, it is easy to see why groups of people who do not drink cow's milk still have strong bones and teeth.
How Much Calcium Do We Need?
The recommended level of calcium for adults age 19 through 50 years is 1000 mg per day2. An intake of 1200 mg of calcium is recommended for those age 51 years and older 2. Some studies 3-5, although not all 3-5, have shown that older adults with a high calcium intake have stronger bones and a lower fracture risk. There are a limited number of studies of vegans, most of which find low bone density as well as low calcium intakes 7,8. One study 9 where vegans had calcium intakes close to recommended levels found that calcium was well absorbed from a vegan diet.
Our Vegan Food Guide (page 198 of Simply Vegan) indicates good sources of calcium from several food groups. By choosing the suggested number of servings of calcium-rich foods daily, vegans should meet calcium needs. Table 2 shows several menus that contain more than 1000 mg of calcium.
Tofu is commonly recommended as a good source of calcium. Actually, the amount of calcium in tofu depends on the coagulating agent used to precipitate the soy protein in the process of making tofu. Calcium sulfate and nigari (magnesium chloride) are two commonly used agents. The agent used will be listed on the label under ingredients. Tofu that is prepared with calcium sulfate will contain more calcium than tofu made with nigari.
The amount of calcium in tofu varies from brand to brand. To calculate how much calcium is in the tofu you buy, look at the label. Calcium content will be listed as percent of the Daily Value. Since the current Daily Value for calcium is 1000 mg, multiply the percent Daily Value by 10 to get the amount of calcium (in milligrams) in one serving. For example, tofu with 10% Daily Value for calcium would have 100 mg of calcium in one serving.
The Influence of Excessive Protein
The area of protein's effect on bones remains uncertain. Some studies show that diets that are high in protein, especially animal protein, do cause increased losses of calcium in the urine 10 and may even in-crease fracture risk 11,12. These effects of protein may be especially important in those with low calcium intakes 13. Other studies suggest that a higher protein intake is needed to promote calcium absorption 14, reduce the risk of fracture 15, and increase bone density 16,17. Until further evidence is available, vegans should strive to meet calcium recommendations and to have adequate, but not excessive, amounts of protein.
Other factors in bone health include sodium and physical activity. Sodium increases calcium losses with 5 to 10 mg of calcium lost with each gram of salt eaten 18. Reducing sodium intake can reduce calcium losses. Regular weight-bearing exercise such as walking, running, or aerobic dance is recommended to promote strong, healthy bones. Besides helping strengthen bones, exercise can also improve balance and flexibility, both important factors in preventing and recuperating from falls.
1.1.Weaver CM, Plawecki KL. Dietary calcium: adequacy of a vegetarian diet. Am J Clin Nutr1994;59 (suppl):1238S-1241S.
2.2.Standing Committee on the Scientific Evaluation of Dietary Reference Intakes, Food and Nutrition Board, Institute of Medicine: Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. Washington, DC: National Academy Press, 1997.
3.3.Chevalley T, Rizzoli R, Nydegger V, et al. Effects of calcium supplements on femoral bone mineral density and vertebral fracture rate in vitamin-D-replete elderly patients. Osteoporos Int1994;4:245-52.
4.4.Dawson-Hughes B, Harris SS, Krall EA, Dallal GE. Effect of calcium and vitamin D supplementation on bone density in men and women 65 years of age or older. N Engl J Med1997;337:670-6.
5.5.Recker R, Hinders S, Davies KM, et al. Correcting calcium nutritional deficiency prevents spine fractures in elderly women. J Bone Miner Res 1996;11:1961-6.
6.6.Feskanich D, Willett WC, Colditz GA. Calcium, vitamin D, milk consumption, and hip fractures: a prospective study among postmenopausal women. Am J Clin Nutr 2003;77:504-11
7.7.Marsh AG, Sanchez TV, Michelsen O. Vegetarian lifestyle and bone mineral density. Am J Clin Nutr 1988;48(suppl):837-41.
8.8.Chiu JF, Lan SJ, Yang CY, et al. Long-term vegetarian diet and bone mineral density in post-menopausal Taiwanese women. Calcif Tissue Int 1997;60:245-9.
9.9.Kohlenberg-Mueller K, Raschka L. Calcium balance in young adults on a vegan and lactovegetarian diet. J Bone Miner Metab 2003;21:28-33.
10.10.Kerstetter JE, O'Brien KO, Insogna KL. Low protein intake: the impact on calcium and bone homeostasis in humans. J Nutr 2003;133:855S-61S.
11.11.Frassetto LA, Todd KM, Morris RC, Jr., et al. Worldwide incidence of hip fracture in elderly women: relation to consumption of animal and vegetable foods. J Gerontol A Biol Sci Med Sci2000;55:M585-92.
12.12.Sellmeyer DE, Stone KL, Sebastian A, et al. A high ratio of dietary animal to vegetable protein increases the rate of bone loss and the risk of fracture in postmenopausal women. Am J Clin Nutr2001;73:118-22.
13.13.Meyer HE, Pedersen JI, Loken EB, et al. Dietary factors and the incidence of hip fracture in middle-aged Norwegians. A prospective study. Am J Epidemiol 1997;145:117-23.
14.14.Kerstetter JE, O'Brien KO, Caseria DM, et al. The impact of dietary protein on calcium absorption and kinetic measures of bone turnover in women. J Clin Endocrinol Metab 2005;90:26-31.
15.15.Munger RG, Cerhan JR, Chiu BC. Prospective study of dietary protein intake and risk of hip fracture in postmenopausal women. Am J Clin Nutr 1999;69:147-52.
16.16.Kerstetter JE, Looker AC, Insogna KL. Low dietary protein and low bone density. Calcif Tissue Int2000;66:313.
17.17.Promislow JH, Goodman-Gruen D, Slymen DJ, et al. Protein consumption and bone mineral density in the elderly: the Rancho Bernardo Study. Am J Epidemiol 2002;155:636-44.
18.18.Heaney RP. Calcium: How your diet affects requirements. Veg Nutr and Health Letter Feb 1998;1(3):1-2.
19.19.Weaver CM, Heaney RP, Nickel KP, et al. Calcium bioavailability from high oxalate vegetables: Chinese vegetables, sweet potatoes, and rhubarb. J Food Sci 1997;62:524-525.
20.20.Weaver CM, Heaney RP, Martin BR, et al. Human calcium absorption from whole-wheat products.J Nutr 1991;121:1769-1775.