Update on Calcium: Do Vegetarians Need Less?

Bone health is extraordinarily complex, and therefore establishing a precise safe level of calcium intake is a difficult task. For one thing, both diet and lifestyle have a big influence on bone health and calcium requirements. Needs also vary dramatically based on genetics, making it difficult to determine desirable intakes for a person, let alone a population.

Of great interest to vegetarians is the idea that people who don't eat meat might need less calcium. We looked at this issue just a year ago, but new findings and new controversies have only made the issue more complex, and we thought an update was in order.

The Protein Connection

It's no secret that dietary calcium throughout the lifespan is essential for strong bones. But calcium intake is just one part of the equation. Guarding against calcium loss is equally important. And maintaining an overall balanced diet is essential, since many other nutrients are involved in building and maintaining strong bones.

Bone density is the biggest factor determining bone fracture risk. Studies suggest that calcium supplements enhance bone density, and some recent research suggests that they reduce risk of fracture.^1,2

But despite these findings, some people question how much calcium intake really affects bone health. Three types of observations challenge the importance of calcium. First, epidemiologic studies within countries often fail to show that people who consume the most calcium have fewer bone fractures. Second, comparisons among countries show that hip fracture rates are higher where people eat calcium-rich diets. Finally, evidence suggests that protein intake--too much protein, that is--causes calcium loss from bones and may be more important than calcium intake in determining bone health.

The protein theory has a sound scientific basis. Clinical studies show that high intake of protein--particularly animal protein--increases calcium excretion in the urine.³ Protein is believed to promote bone loss because it is acid-producing. The body buffers this acid condition--which would otherwise be deadly--through a complex series of reactions that involve release of calcium from the bone. So it makes sense that eating too much protein will increase calcium needs, and that those who eat less protein, like vegetarians, will have lower calcium needs.

We need to exercise some caution in interpreting these findings, though. First, while excess protein may be bad for bones, adequate protein is essential for bone health, and many older Americans may not consume enough protein. It's also possible that some vegan women have protein intakes that are only marginally adequate.⁴ A number of studies indicate that protein supplements speed healing of fractured bones in older people.⁵

Also, some research suggests that protein enhances calcium absorption.⁶ This may partially explain the increased urinary losses, which may be due to excess calcium that the body has absorbed but doesn't need. While this is not a widely held view, it's an important observation, since it demonstrates that what we know about protein and calcium is, to some degree, still open to interpretation.

An interesting observation is that hip fracture rates are lowest in countries where protein intake is low--even though calcium intake is low in these countries as well.⁷ This would be a strong piece of evidence suggesting that protein is a more important factor than calcium in bone health. However, among many experts, these cross-cultural comparisons are now recognized as being largely unimportant. One reason is that these comparisons of hip fracture are not necessarily a good indicator of overall bone health. In fact, in some countries like Japan where hip fracture rates are low, spinal fractures are actually more common than in western countries--a good indication that hip fracture does not tell the whole story about bone health.⁸ Furthermore, there are genetic differences in hip anatomy that may affect fracture rates. For example, Asians, who experience fewer hip fractures than westerners despite their lower calcium intakes, have a shorter hip axis, length which makes it significantly more resistant to breakage.⁹ Furthermore, Japanese people have better balance and are only half as likely to fall as westerners. Since 90 percent of all hip fractures are due to falls, this is an important factor affecting fracture rates.¹⁰

Also, some evidence suggests that people of Asian descent absorb calcium more efficiently.¹¹ And people of African descent actually metabolize calcium differently and in a way that enhances bone health.¹² People in developing countries where both calcium and protein intakes are low are also much more likely to be physically active, and there is wide consensus among experts that being physically active is crucial to good bone health. Finally, there are other dietary factors that may affect these hip fracture comparisons. People in Scandinavian countries, for example, may have a high intake of vitamin A from animal food sources, which may be linked to poorer bone health.¹³ And high intake of sodium is associated with increased calcium losses. In fact, sodium appears to have a bigger effect on calcium excretion than protein.¹⁴

In short, comparing rates of hip fractures among different cultures and countries tells us little about the relationship between protein and calcium and bone health. So what happens when we turn our attention to comparisons of calcium intake among people within a country? Unfortunately, we don't learn much from these studies either. Most show that people with higher calcium intake are no more likely to have fewer fractures than those with low intake.¹⁵ But we can't be so fast to dismiss the effects of calcium, based on these observations. As for cross-cultural studies, myriad factors affect bone health. These include protein, exercise, sodium, vitamin D, vitamin K, smoking, and heredity. And, because calcium absorption varies dramatically among individuals, it is difficult to identify protective effects of calcium in a given population. It is also very difficult to accurately measure calcium intake in a population. Simply looking at consumption patterns of a group of people doesn't provide enough data to build--or negate--a case for the relationship between calcium and bone health. This may help to explain why controlled clinical studies show an effect of measurable calcium supplement intake, while observational studies show little or no effect of calcium from food.

Vegetarian Calcium Needs

Unfortunately, we don't have much to go on in determining calcium needs of vegetarians. The lower protein intake of vegetarians--especially of vegans--may suggest a lower calcium need, since the best evidence is that animal protein in particular has a negative effect on calcium balance. But as we have seen, the relationship among these factors is not that clear. It is likely that the ratio of calcium to protein in the diet is probably one factor affecting bone health. On average, lacto-ovo vegetarian diets have the best ratio. Both omnivores and vegans have poorer ratios--vegans because their calcium intake tends to be low, and omnivores because they consume too much protein and also have calcium intakes lower than recommendations (at least for omnivore women).

Most of what we know about bone health of lacto-ovo vegetarians shows that their bone health is as good as or better than omnivores'.¹⁶ There is little information about vegan bone health, although a few preliminary studies suggest that bone density is poorer in vegan women than in those who consume dairy foods. This doesn't mean there is anything inherently unhealthy about vegan diets; it does suggest that many vegan women may not eat diets that supply enough calcium and should boost their intake of plant foods that are naturally rich in calcium or that are calcium-fortified.

However, one potentially important consideration--albeit a speculative one--is that vegetarian women tend to have lower blood levels of estrogen. Although this may lower breast cancer risk, it may not be good for bones, since estrogen promotes bone health.

It is probable that people who consume diets that are low in sodium and moderate in protein and who exercise regularly have lower calcium needs than those who eat copious amounts of protein and salt and lead a couch-potato lifestyle. But in terms of general recommendations, we can't conclude that vegetarians as a group need less calcium than omnivores.

Pending a better understanding of calcium needs of all groups, vegetarians should aim to meet the current calcium recommendation for their age group. Clearly, however, bone health is not a one-nutrient issue. All the calcium in the world will not do you much good if you don't exercise, don't get adequate vitamin D, eat too much salt, and have a diet that is generally unbalanced. Calcium is important, but it's only one of many important factors.

Meeting Calcium Needs

Make the most of your food choices. Choose calcium-fortified soymilk, rice milk, and orange juice over the unfortified brands. Tofu is made with a variety of salts; look for types made with a calcium salt like calcium sulfate. Be sure to include several very rich sources of calcium in your diet every day--nonfat cow's milk, fortified nondairy milks, fortified juices, or calcium-set tofu. And look for ways to incorporate other sources of calcium into your diet as well. Try some of these tips:

• Toss raw greens like kale with onions and garlic sauteed in olive oil and with just a pinch of cinnamon. Then cook them in a small amount of vegetable broth until tender.
• Make a calcium-rich smoothie by combining 1 cup calcium-fortified orange or apple juice, 4 ounces of calcium-set tofu, and a ripe banana.
• Add chopped fresh or dried figs (soak dried figs in hot water for a few minutes first) to cannellini, navy, or great northern beans seasoned with onions and garlic.
• Toss a handful of soynuts into salads.
• We sing the glories of peanuts in this issue (see page 7) but you can boost calcium intake by trading the peanut butter in your sandwich for calcium-rich almond butter.
• Make a calcium-rich Asian stir-fry by teaming up chunks of calcium-set tofu, broccoli florets, and sliced bok choy (add the bok choy towards the end of cooking time as it cooks in a flash).
• Enjoy calcium-rich desserts like puddings and tapioca. You can make them with low-fat milk or nondairy milks.
• Give homemade baked beans extra flavor and nutrition with a couple tablespoons of blackstrap molasses. Only blackstrap, not regular, molasses is a good source of calcium (and the beans have calcium, too).

1. J Clinical Endocrinol Metabol 83: 3817-3825, 1998

2. N Engl J Med 337: 670-676, 1997 (calcium and vitamin D suppl
and fractures)

3. J Nutr 112:338-349, 1982.

4. Br J Nutr 69: 3-19, 1993.

5. Ann Intern Med. 128:801-9, 1998.

6. Am J Clin Nutr. 1998 Oct;68(4):859-65.

7. Calcif Tissue Int 50:14-18, 1992

8. Int J Epidemiol 24: 1171-1177, 1995.

9. Osteoporosis Int 4: 226-229, 1994

10. Bone 18: 65S-75S, 1996

11. Am J Clin Nutr 1998; 68: 1291-7

12. J Lab Clin Med. 132:358-9, 1998

13. Ann Intern Med. 129:770-8, 1998.

14. Am J Clin Nutr. 67:438-44, 1998.

15. Am J Clin Nutr 69: 147-152, 1998.