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Calcium in the Vegan Diet

by Reed Mangels, Ph.D., R.D.


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Summary

Calcium, needed for strong bones, is found in dark green leafy vegetables, tofu made with calcium sulfate, and many other foods commonly eaten by vegans. High protein diets appear to lead to increased calcium losses. Calcium requirements for those on lower protein, plant-based diets may be somewhat lower than requirements for those eating a higher protein, flesh-based diet. However, it is important for vegans to eat foods regularly that are high in calcium and/or use a calcium supplement.

The Need for Calcium

Calcium is a very important mineral in the human body. 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. Calcium in the blood is tightly controlled by the body, so calcium status cannot be assessed by measuring blood calcium levels.

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 need not be concerned about getting adequate calcium. Table 1 shows the amount of calcium in selected foods. When you realize that there is as much calcium in 4 ounces of firm tofu or 3/4 cups 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.

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 which 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 milligrams, multiply the percent Daily Value by 10 to get the amount of calcium (in milligrams) in one serving. For example, tofu with 10% of the Daily Value for calcium would have 100 milligrams of calcium in one serving.

How Much Do We Need?

How much calcium do we need? The reccommended level of calcium for adults age 19 through 50 years is 1000 milligrams per day [1]. An intake of 1200 milligrams of calcium per day is recommended for those age 51 years and older [1]. In other countries, calcium recommendations are lower, as low as 600 milligrams daily for adults[2-4] Does only science influence these recommendations or are political and economic factors also at work? (Read Nutrition Action Health Letter from Center for Science in the Public Interest, Vegetarian Journal, Nutrition Week from the Community Nutrition Institute, Advertising Age, and National Dairy Council materials for insight into forces shaping recommendations.)

The Influence of Excessive Protein

Calcium needs appear to be influenced by both protein and sodium intakes. High protein diets seem to markedly increase the amount of calcium lost from the body every day [5-6]. In fact, when young adults had a protein intake of 48 grams per day (slightly lower than the current RDA) they had no net loss of calcium, even though the amount of calcium in their diet was as low as 500 milligrams daily [7]. It has been estimated that for every gram of protein consumed, calcium losses in urine increase by about 1 milligram [6]. Because we only absorb about 10% of the calcium which we eat, this means that for every gram of protein, we would need to take in 10 extra milligrams to make up for urine losses [8].

It is much more likely that protein intakes will be excessive on a meat-based diet or a diet high in dairy products as shown in Table 2. In addition, it appears that soy protein, even at high levels, does not increase calcium excretion the same way that protein from animal sources does [5]. Diets which are too low in protein (around 44 grams a day) also appear to have a negative effect on calcium status [9]. Sodium also increases calcium losses with 5 to 10 milligrams of calcium lost with each gram of salt eaten [8].

Calcium requirements for those on lower protein, plant based diets may be somewhat lower than requirements for those eating a higher protein, flesh-based diet. However, it is important for vegans to regularly eat foods high in calcium and/or use a calcium supplement.

We recommend that three or more servings of good sources of dietary calcium Table 1 be eaten daily by adults (4 or more servings for those age 51 and older), along with the use of a diet without excessive protein. Regular weight-bearing exercise such as walking, running, or aerobic dance is also recommended to promote strong, healthy bones. Table 3 shows several menus which contain more than 1000 milligrams of calcium.

What About Osteoporosis?

What about osteoporosis? Don't vegans need extra calcium to prevent osteoporosis? In osteoporosis, bones become porous and fragile. The Dairy Council leads us to believe that milk is essential to prevent osteoporosis. In reality, many other foods besides milk (see Table 1) provide calcium, often without the high dose of protein seen in milk. Researchers studied close to 78,000 women and 43,000 men and found that higher intakes of calcium rich foods during the adult years did not reduce risk of fractures [13-14]. Many factors lead to osteoporosis and there are a number of possible explanations for these findings.

Other factors which increase the risk of osteoporosis include small frame size, female gender, aging, heredity, cigarette smoking, excessive alcohol, Caucasian or Oriental race, steroid use, early menopause, prolonged immobilization, and inadequate vitamin D.

The most promising way that nutrition can reduce the risk of osteoporosis is by promoting development of a favorable peak bone mass during the first 3 to 4 decades of life. Several studies have shown that lacto-ovo vegetarians have the same [15-16] or larger [17] bone masses than do omnivores. We have little information about the bone health of vegans. A study which included 8 vegan women found that their bone density was not significantly from that of lacto-ovo vegetarians [18]. A study of only 11 elderly vegan women found lower bone density in vegans although this may not be due to the vegan diet since some of the subjects had been vegan for only 2 years [19] . Further studies of bone mass of vegans of all ages are needed.


Table 1: Calcium Content of Selected Vegan Foods


Food					Amount	Calcium (mg)
Soy or ricemilk, commercial,		8 ounces	150-500
	calcium-fortified, plain
Collard greens, cooked			1 cup		357
Blackstrap molasses			2 Tbsp		342
Tofu, processed with calcium
	sulfate*			4 ounces	200-330 
Calcium-fortified orange juice		8 ounces	300
Commercial soy yogurt, plain		6 ounces	250
Turnip greens, cooked			1 cup		249 
Tofu, processed with nigari*		4 ounces	80-230
Kale, cooked 				1 cup		179
Okra, cooked				1 cup		176
Soybeans, cooked			1 cup		175
Sesame seeds				2 Tbsp		160
Bok choy, cooked			1 cup		158
Tempeh					1 cup		154
Mustard greens, cooked			1 cup		152
Figs, dried or fresh			5 medium	135
Tahini					2 Tbsp		128
Almonds					1/4 cup		97
Broccoli, cooked			1 cup		94
Almond butter				2 Tbsp		86
Soymilk, commercial, plain		8 ounces	80
*Read the label on your tofu container to see if it is processed with calcium sulfate or nigari.

Note: Oxalic acid, which is found in spinach, rhubarb, chard, and beet greens is often said to bind with calcium and reduce absorption. These foods should not be considered good sources of calcium. Calcium in other green vegetables, like kale, collard greens, Chinese mustard greens, and Chinese cabbage flower leaves is well absorbed.[10-11]. Fiber appears to have little effect on calcium absorption except for the fiber in wheat bran which does have a small effect [12]

Sources: Composition of Foods. USDA Nutrient Data Base for Standard Reference, Release 12, 1998. Manufacturer's information.


Table 2: Protein Content of Selected Foods


Food					Amount		Protein (gm) 

Cow's milk				8 ounces		8
Egg					1			6
Salmon, pink, canned			4 ounces		22
Beef, ground, lean, baked 		4 ounces		27
Chicken, baked				4 ounces		37
Adapted from Havala, S.: Osteoporosis, Beyond a Simple Answer. Vegetarian Journal 5:11, 1986.


Table 3: Sample Menus Providing More Than 1000 milligrams of Calcium


							Calcium (mg)
Breakfast:
	1 serving Cindy's Light and
		Fluffy Pancakes (p. 23)			195
	1 cup Plain Soymilk				80

Lunch:
	1 serving Hummus on Pita Bread (p. 27)		178
	6 Dried Figs					162
	1/4 cup Almonds					97

Dinner:
	1 serving Scramble Tofu and Bok
		Choy over Brown Rice (P. 96)		190
	1 serving Green Salad and 
		Tangerine Dressing (p. 39)		 30
	1 serving Chocolate Pudding (p. 114)		 92
							---
TOTAL							1024



Breakfast:
	1 serving Tropical Fruit Smoothie (p. 16)	102
	1 toasted bagel with				66
	2 Tbsp Almond Butter	 			86

Lunch:
	1 serving Mini Pizzas (p. 34)			235
	1 serving Creamed Spinach (p. 68)		121

Dinner:
	1 serving Lemon Rice Soup (p. 46)		 82
	1 serving Tofu Squash Burgers (p. 102)		135
	1 cup steamed Broccoli				 94
	 with 1 Tbsp Sesame Seeds			 80
							---
TOTAL							1001

Page numbers refer to recipes in the book Simply Vegan.

Additional foods should be added to these menus to provide adequate calories and to meet requirements for nutrients besides calcium.


References

1. 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.

2. Report on Health and Social Subjects: No. 41, Dietary Reference Values for Food Energy and Nutrients for the United Kingdom. Report of the Panel on Dietary Reference Values of the Committee on Medical Aspects of Food Policy. London: HMSO, 1991.

3. Recommended Dietary Allowances for Japan. Tokyo, Japan: Ministry of Health and Welfare, 1991.

4. Recommended Daily Dietary Allowances, Korea. Kyongi, Korea: Ministry of Health and Social Affairs, 1989.

5. Zemel MB: Calcium utilization: Effect of varying level and source of dietary protein. Am J Clin Nutr 1988; 48: 880-883.

6. Kerstetter JE and Allen LH: Dietary protein increases urinary calcium. J Nutr 1990; 120: 134-136.

7. Linkswiler HM, Zemel MB, Hegsted M, Schuette S: Protein-induced hypercalciuria. Fed Proc 1981; 40: 2429-2433.

8. Heaney RP. Calcium: How your diet affects requirements. Veg Nutr and Health Letter Feb 1998; 1(3): 1-2.

9. Kerstetter JE, Caseria DM, Mitnick ME, et al. Increased circulating concentrations of parathyroid hormone in healthy, young women consuming a protein restricted diet. Am J Clin Nutr 1997; 66:1188-1196.

10. Weaver, CM, Plawecki KL: Dietary Calcium: adequacy of a vegan diet. AM J Clin Nutr 1994; 59 (Suppl.): 1238S-1241S.

11. 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.

12. Weaver CM, Heaney RP, Martin BR, et al. Human calcium absorption from whole-wheat products. J Nutr 1991; 121: 1769-1775.

13. Feskanich D, Willet WC, Stampfer MJ, Colditz GA. Milk, dietary calcium, and bone fractures in women: A 12 year prospective study. Am J Public Health 1997; 87: 992-997.

14. Owusu W, Willett WC, Feskanich D, et al. Calcium intake and the incidence of forearm and hip fractures among men. J Nutr 1997; 127: 1782-1787.

15. Hunt IF, Murphy NJ, Henderson C et al: Bone mineral content in postmenopausal women: comparison of omnivores and vegetarians. Am J Clin Nutr 1989; 50: 517-523.

16. Marsh AG, Sanchez TV, Chaffee FL et al: Bone mineral mass in adult lacto-ovo-vegetarian and omnivorous males. Am J Clin Nutr 1983; 37: 453-456.

17. Marsh AG, Sanchez TV, Mickelsen O et al: Cortical bone density of adult lacto-ovo-vegetarian and omnivorous women. J Am Diet Assoc 1980; 76: 148-151.

18. Barr SI, Prior JC, Janelle KC, et al. Spinal bone mineral density in pre-menopausal vegetarian and nonvegetarian women: cross sectional and prospective comparisions. J Am Diet Assoc 1998; 98: 760-765.

19. Marsh AG, Sanchez TV, Michesen O, et al. Vegetarian life-style and bone mineral density. Am J Clin Nutr 1988; 48: 837-841.


SIMPLY VEGAN COVER This article originally appeared in the book Simply Vegan: Quick Vegetarian Meals by Debra Wasserman. Nutrition section by Reed Mangels Ph.D., R.D. (ISBN 0-931411-20-3)

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