Calcium Information

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

Summary: Calcium, needed for strong bones, is found in dark green vegetables, tofu processed 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 are believed to be below the usual recommendations. _____________________________________________

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.

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 9 (see below) shows the amount of calcium in selected foods. When you realize that there is as much calcium in 5 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 U.S. RDA (often 10 or 15%). Since the current U.S. RDA for calcium is 1000 milligrams,multiply the percent U.S. RDA by 10 to get the amount of calcium (in milligrams) in one serving. For example, tofu with 10% of the U.S. RDA for calcium would have 100 milligrams of calcium in one serving.

How much calcium do we need? The RDA for adults age 25 and older is 800 milligrams of calcium per day (1). An intake of 1200 milligrams of calcium per day is recommended for those age 11-24. In other countries, calcium recommendations are lower than in the US. For example, British adults are advised to have a calcium intake of 500 milligrams per day (2) and adults in Japan are told to have 600 milligrams of calcium daily (3). 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, Guide to Healthy Eating from Physician's Committee for Responsible Medicine, Nutrition Week from the Community Nutrition Institute, Advertising Age, and National Dairy Council materials for insight into forces shaping recommendations.)

Calcium requirements may be influenced by high protein intakes (4). 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). In contrast, when young adults were on a diet high in protein (112 grams-- typical of many Americans), they lost substantial amounts of calcium in their urine, even when calcium intakes were as high as 1400 milligrams per day (7).

Although phosphorus, another mineral found in foods which are high in protein, does reduce the effects of protein on calcium somewhat,calcium status appears to be more affected by the amount of protein in the diet (5, 6). A protein intake above 70 grams per day is not recommended (6). Of course, this level of protein intake is likely to be exceeded on a meat-based diet or a diet high in dairy products. As Table 10 (see below) shows, by eating 2 servings of meat or fish, an egg, and 2 cups of milk every day, a person would come close to exceeding the 70 gram upper limit for protein without even considering other protein sources such as breads and vegetables. _____________________________________________

Table 9: Calcium Content of Selected Vegan Foods

Food Amount Calcium (mg)

Tofu, firm, processed with calcium 4 ounces 250-765 sulfate*

Tofu, regular, processed with calcium 4 ounces 120-392 sulfate*

Collard greens, cooked 1 cup 357

Rhubarb, cooked 1 cup 348

Spinach, cooked 1 cup 278

Blackstrap molasses 2 TB 274

Turnip greens, cooked 1 cup 249

Tofu, firm, processed with nigari* 4 ounces 80-230

Kale, cooked 1 cup 179

Sesame seeds 2 TB 176

Okra, cooked 1 cup 176

Soybeans, cooked 1 cup 175

Beet greens, cooked 1 cup 165

Bok choy, cooked 1 cup 158

Tempeh 1 cup 154

Mustard greens, cooked 1 cup 150

Figs, dried or fresh 5 medium 135

Tahini 2 TB 128

Tofu, regular, processed with nigari* 4 ounces 80-146

Swiss chard, cooked 1 cup 102

Almonds 1/4 cup 97

Broccoli, cooked 1 cup 94

Almond butter 2 TB 86

Soymilk, commercial, plain 8 ounces 84

*Read the label on your tofu container to see if it is processed with calcium sulfate or nigari.

The RDA for calcium for adults, 25 and older, is 800 milligrams per day; for those 11-24, the RDA is 1200 milligrams of calcium. United States recommendations are more than 50% higher than the British and Japanese.

Note: Oxalic acid, which is found in spinach, rhubarb, chard, and beet greens is often said to bind with calcium and reduce absorption.In laboratory experiments, calcium does combine with oxalates. However,at normal dietary intakes, oxalates have little practical effect on calcium absorption (1).

Sources: Composition of Foods. USDA Handbook 8. Manufacturer's information. _____________________________________________

The type of protein may also be important. At least one study shows that soy protein, even at high levels, does not increase calcium excretion the same way that protein from animal sources does (5).

The RDAs for calcium were made for people consuming typical American high protein diets. Many vegan diets are lower in protein than these typical American diets. For those whose protein intake is lower, but adequate, or whose protein is from non-animal sources,calcium intakes below the RDA are probably adequate.

We recommend that two or more servings of good sources of dietary calcium be eaten daily by adults, along with the use of a diet without excessive protein. Teenagers and young adults (age 20-25) should eat 3 or more servings of foods high in calcium. Regular weight-bearing exercise such as walking, running, or aerobic dance is also recommended to promote strong, healthy bones. Table 11 (see below)shows several menus which contain more than 800 milligrams of calcium. _____________________________________________

Table 10: 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 4 ounces 26

Chicken 4 ounces 19

Adapted from Havala, S.: Osteoporosis, Beyond a Simple Answer. Vegetarian Journal 5:11, 1986. __________________

Table 11: Sample Menus Providing More Than 800 milligrams of Calcium

Calcium (mg) Breakfast: 1 serving Cindy's Light and Fluffy Pancakes (p. 23) 210

Lunch: 1 serving Hummus on Pita Bread (p. 27) 178 5 dried figs 135

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 835 _____________________________________________

Breakfast: 1 serving Tropical Fruit Smoothie (p. 16) 102 1 toasted bagel with 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 ---TOTAL 855

Additional foods should be added to these menus to provide adequate calories and to meet additional nutrient requirements. _____________________________________________

Vegetarian, and especially vegan, diets are often high in fiber due to frequent use of whole grains, beans, fruits, and vegetables. This maybe one reason why vegetarians have a lower incidence of heart disease and some kinds of cancer than does the general public. However, one concern with diets high in fiber is that the fiber can bind with minerals, like calcium, in the intestine and thus keep the minerals from being absorbed. Vegan diets may contain 40 or more grams of fiber per day (8). Dietary fiber intakes of 35 grams or less are not believed to have a significant impact on mineral absorption(9). However, humans may be able to adapt to diets with more than 35 grams of dietary fiber, so that, in time, these diets have little effect on calcium absorption. This adaptation apparently occurs in vegans since bone density of vegans appears to be normal (10). If calcium absorption was impaired, bone density of vegans would be expected to be low.

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 9, above) provide calcium, often without the high dose of protein seen in milk.

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

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 vegetarians have the same (11, 12) or larger (13) bone masses than do omnivores.

References

1. Food and Nutrition Board, National Research Council: Recommended Dietary Allowances, 10th ed. Washington, DC: National Academy Press, 1989.

2. Department of Health and Social Security: Recommended Daily Amounts of Food Energy and Nutrients for Groups of People in the United Kingdom. London: HMSO, 1979.

3. Recommended Dietary Allowances for Japan. Tokyo, Japan: Ministry of Health and Welfare, 1984.

4. Food and Nutrition Board, National Research Council: Recommended Dietary Allowances, 9th ed. Washington, DC: National Academy Press, 1980.

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

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

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

8. Roe LS, Thorogood M, Mann JI: Diet and plasma lipids in a group of vegetarians and omnivores. Proc Nutr Soc 49: 59A, 1990.

9. Kelsay JL: Update on fiber and mineral availability. In Vahouny GW and Kritchevsky D (eds): Dietary Fiber. New York: Plenum Publishing Corporation, 1986; 361-372.

10. Ellis FR et al: Incidence of osteoporosis in vegetarians and omnivores. Am J Clin Nutr 25: 555-558, 1972.

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

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

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

This article was originally published in Simply Vegan,published by: The Vegetarian Resource Group, P.O. Box 1463 Baltimore, MD 21203, (410) 366-VEGE

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Our health professionals, activists, and educators work with businesses and individuals to bring about healthy changes in your school, workplace, and community. Registered dietitians and physicians aid in the development of nutrition-related publications and answer member and media questions about vegetarian diets. The Vegetarian Resource Group is a non-profit organization. Financial support comes primarily from memberships, contributions, and book sales.

For questions or comments on this article, please contact Bobbi Pasternak at bobbi@clark.net. This article is copied with the permission of the authors.Copyright 1991 by Debra Wasserman and Reed Mangels, Ph.D., R.D. The contents of this article, as with all The Vegetarian Resource Group publications, is not intended to provide personal medical advice.Medical advice should be obtained from a qualified health professional.