Boning up on Calcium and Osteoporosis
It is a common myth that people should increase their calcium intake.
Mostly, they are encouraged to take supplements and to drink more milk. But
milk may not "do a body good." The highest rates of osteoporosis are in the
industrialized Western nations--the biggest consumers of milk. It turns out
that keeping strong bones depends more on preventing calcium loss than on
increasing calcium intake.
Calcium in the Body
Almost all of the calcium in the body is in the bones. There is a tiny
amount in the blood stream which is responsible for muscle contraction,
maintenance of the heartbeat, and transmission of nerve impulses and other
functions. Hormones control the amount of calcium in the blood. Everyone
constantly loses calcium through urine, sweat, and feces, and it is renewed
with calcium from the bones. In the process, the body constantly breaks
down and rebuilds bones. Ultimately, the body's calcium is replaced by
calcium from food.
Reducing Calcium Loss
Since the 1920's researchers have known that diets that are high in
protein, especially animal protein, cause calcium to be lost through the
urine.1 In nations with high rates of osteoporosis, protein intake is
generally high~usually more than twice the U.S. Recommended Daily
Allowance. Vegetarians have lower rates of osteoporosis than meat eaters.
This may be due to the lower protein intake of vegetarians. Different types
of protein also affect this loss. Meats are overly high in protein and are
high in a particular kind of protein building block, called sulfur-
containing amino acids. These cause increased calcium loss.2
Caffeine and sodium also increase the rate at which calcium is lost
through urine. Alcohol inhibits calcium absorption and may also be toxic
to bone.3 Vitamin D, copper, zinc, manganese, fluorine, and boron are all
essential for good bone formation, and weight-bearing exercise also
increases bone mass and helps to prevent osteoporosis.4 Boron appears to
help stop the loss of calcium. The best way to get boron is through fruits,
vegetables, and beans.
The Need for Calcium
Throughout life, people's calcium needs change. Until about age 35,
people consume more calcium that their bodies lose. But around age 45, the
body begins to slip into "negative calcium balance"~slowly the body loses
more calcium than it takes in. As shown above, how rapidly calcium is lost
depends, in part, on how much protein is in the diet, and the kind of
protein it is. The loss of too much calcium can lead to "soft bones," or
osteoporosis.
Fighting Bone Loss
Most studies have shown that high doses of calcium do not slow bone loss.
In fact, many populations with high intakes of calcium also have high rates
of osteoporosis,5 probably because their high protein intake causes
significant calcium loss. Some African cultures consume no dairy products
and typically get only 175 to 475 milligrams of calcium per day (800mg is
the U.S. RDA), but they have low rates of osteoporosis. Rates of hip
fracture among different populations is one way researchers measure the
prevalence of osteoporosis. One such study of ten nations revealed that as
calcium intake increased, so did the number of hip fractures. Such studies
have also led researchers to believe that exercise and other factors have
more to do with preventing osteoporosis than calcium intake does.
Absorbing Calcium
The body carefully regulates its calcium absorption. The average person
absorbs 30 to 70 percent of the calcium she or he eats, but the more
calcium taken in, the less the body will absorb. This is to protect the
body from overdosing on calcium. At the U.S. RDA of 800mg, the body may
absorb as little as 15 percent of the total amount. This may be one reason
that high calcium intake does not generally prevent bone loss.
While milk is a source of calcium, it certainly is not the ideal way to
get your daily dose. Dairy products, with the exception of skim products,
are loaded with saturated fat. Fat is directly related to heart disease and
cancer. Dairy products are also high in protein. There are other reasons
to worry about milk, too. Cows are routinely fed antibiotics. These are
then passed directly on to the milk drinkers; antibiotics are detectable
in one out of three cartons of milk. Many people are also allergic to milk,
and over three-fourths of the world's population is lactose-intolerant,
which means their bodies lack the enzymes necessary to digest milk.
Great Sources of Calcium
Dark green vegetables, such as broccoli and collard, mustard, and turnip
greens are much better sources of calcium than milk. A single cup of
broccoli contains almost a fourth of the U.S. RDA of calcium. Another good
source is calcium-fortified orange juice. Beans and tortillas are also good
sources of calcium.
Some people do need hormone treatments and/or calcium supplementation for
varying conditions. The risks and benefits should be discussed with one's
doctor.
Conclusion
Calcium is an essential nutrient and is needed for healthy
bones particularly during childhood and adolescence. While it is uncertain
how much calcium is actually needed, it is certain that diet affects
calcium balance. Calcium supplements are not the best way to control
osteoporosis for most people. A diet that is modest in protein,
complemented by exercise, is much more effective. Green leafy vegetables
and beans are good sources of calcium that are also moderate in protein and
very low in fat.
References:
1. Hegsted M, Schuette SA, et al. Urinary calcium and calcium balance in
young men as affected by level of protein and phosphorus intake. J Nutr
1981;111:553-562.
2. Marsh AG, Sanchez TV, et al. Cortical bone density of adult lacto-ovo-
vegetarian and omnivorous women. J Am Diet Asso 1980;76:148-150.
3. Rivlin, RS. Women's health: osteoporosis. Public Health Reports
1986;131-135.
4. Schaafsman F, van Beresteyn ECH, et al. Nutritional aspects of
osteoporosis. Wld Rev Nutr Diet 1987;49:121-159.
5. Hegsted DM. Calcium and Osteoporosis. J Nutr 1986;116:2316-2319.
Calcium is found in a variety of plant foods. The following are low-fat,
cholesterol-free sources of calcium.
Food Amount Milligrams of Calcium
Collard Greens 1 cup 355 mg
Bok Choy 1 cup 250 mg
Turnip Greens 1 cup 200 mg
Kale 1 cup 200 mg
Broccoli 1 cup 180 mg
Kelp (Seaweed) + cup 170 mg
Mustard Greens 1 cup 150 mg
Wakame (Seaweed) + cup 150 mg
Blackstrap Molasses 1 tablespoon 140 mg
Amaranth + cup 140 mg
Great Northern Beans 1 cup 140 mg
Dried Figs 5 figs 135 mg
Vegetarian Baked Beans 1 cup 130 mg
Navy Beans 1 cup 130 mg
Corn Tortilla 1 tortilla 120 mg
Fortified Orange Juice 6 ounces 120 mg
Kidney Beans 1 cup 115 mg
Black Beans 1 cup 105 mg
Okra 1 cup 90 mg
Acorn Squash 1 cup 90 mg
Pinto Beans 1 cup 85 mg
Tofu* + cup 130 mg
Soybeans* 1 cup 175 mg
* may be high in fat
Physicians Committee for Responsible Medicine
P.O. Box 6322
Washington, DC 20015
(202) 686-2210
Jonathan Esterhazy / Manitoba Animal Rights Coalition