Calcium, the essential mineral that helps build strong bones and teeth, is emerging as an important player in maintaining health in a host of other ways, from controlling high blood pressure and reducing the symptoms of premenstrual syndrome to perhaps even protecting against colon cancer.
At a calcium summit held June 25 in Washington and sponsored by the National Dairy Council, federal health officials, researchers and physicians underscored the growing appreciation for the many roles that calcium plays. "In simplest terms, we need calcium in our diets because life is impossible without it," said Robert P. Heaney, professor of medicine at Creighton University's Osteoporosis Research Center in Omaha, Neb.
Long acknowledged as an important component of bones and teeth, calcium also helps keep blood pressure in check, conference participants said. In the recent Dietary Approaches to Stop Hypertension (DASH) study, researchers at the National Heart, Lung and Blood Institute tested the effects of three eating plans: Standard American fare was compared against a diet high in fruits and vegetables and a combination diet that was rich in fruits, vegetables and low-fat dairy products.
The study, published in 1997, found that the degree of blood pressure reduction from the combination eating plan was comparable to that of some anti-hypertensive medications. By comparison, the diet rich in fruits and vegetables was about half as effective as the combination diet in controlling blood pressure.
Calcium is believed to lower blood pressure by promoting the production of nitrous oxide, a substance that causes blood vessels to relax and open up, thereby causing less resistance in flow.
If more people adopted the dairy-rich DASH eating plan, the United States could see significant improvements in rates of stroke and heart disease, McCarron said. "Science is moving here at a logarithmic pace," he said. "It took us 40 years to find the connection between calcium and osteoporosis and 15 years for blood pressure. It's why I think that we will find other indications for calcium at a faster pace in the next 10 years."
One of the newest frontiers for calcium is in colon cancer prevention. Laboratory, clinical and population studies suggest that a diet high in calcium may protect against this widespread disease. Colon cancer is the second leading cause of cancer deaths in the United States today. The American Cancer Society estimates that nearly 100,000 new cases of colon cancer will be diagnosed in 1999 in the United States and that 50,000 people will die from the disease.
Colon cancer develops from tiny polyps that are the result of rapidly multiplying cells in the lining of the intestine. Why these cells develop into polyps is not completely understood, but the theory is that a high-fat diet produces high amounts of fatty acids in the intestine, which accelerate the cell proliferation.
Growing evidence suggests that calcium can slow this process by binding to fatty acids and bile acids. "This makes them unavailable to irritate the colon," said Peter Holt, professor of medicine at Columbia University's College of Physicians and Surgeons in New York.
Studies have found that both calcium supplements and calcium-rich foods can help achieve these changes. But research points to a particularly beneficial effect from low-fat dairy foods, perhaps, Holt said, "because of other components, including vitamin D, that may work together with calcium to produce these positive changes."
The trouble is that most Americans still don't consume enough calcium to meet the recommended daily intake levels. Teenagers are at particular risk. Bone density increases most from ages 12 to 19, precisely the time when daily calcium intake generally plummets. "Teenagers do what they want," the University of Colorado's Susan Johnson told the summit.
Many adolescents switch from milk to soft drinks that not only lack calcium but also rob calcium from growing bones. The recommended intake of calcium for teenagers is 1,300 milligrams per day. Adolescent girls average 800 milligrams, according to the latest figures from the National Health and Nutrition Examination Survey (NHANES). NHANES found that adolescent boys do better, averaging nearly 1,200 milligrams per day, but still fail to meet the adequate daily intake.
The optimum calcium intake can be achieved in many ways, particularly with the growing number of fortified foods, beverages and supplements available. "It doesn't have to be milk," said McCarron, who consults with the National Dairy Council.
Scientific evidence suggests that foods high in calcium--and dairy products are among the highest--pack more punch. "The evidence is mounting that there's a 40 to 50 percent more effect when calcium comes from dietary sources than supplements," McCarron said.
Concern about the low calcium intake in the United States is so great among public health officials that the federal government has begun campaigns to boost calcium levels. One target is osteoporosis, the debilitating bone disease that afflicts 10 million Americans, according to the National Osteoporosis Foundation. An estimated 18 million more people have low bone mass, a condition that places them at increased risk for osteoporosis.
Osteoporosis results in gradual loss of bone that leaves patients prone to painful fractures. The Osteoporosis Foundation estimates that one in two women and one in eight men over age 50 will have an osteoporosis-related fracture in their lifetime.
Until recently, osteoporosis has largely been considered a disease of Caucasians. But new findings show that it afflicts all races and ethnic groups. Estimates are that 10 percent of African American women over age 50 have osteoporosis; an additional 30 percent have low bone density that puts them at risk of developing osteoporosis, according to the Osteoporosis Foundation.
Because thinning of the bones takes years to occur, osteoporosis does not show up until midlife and later. But the foundations for this disease are laid in childhood.
"Osteoporosis is a pediatric disease with geriatric consequences," said Duane Alexander, director of the National Institute of Child Health and Human Development. "By age 17, 90 percent of adult bone mass is established."
To help combat the low calcium intake among children and teens, NICHD has launched "Milk Matters!", a public health campaign designed to encourage milk consumption among school children.
"Why milk?" Alexander said. "Because milk and dairy products have a lot of calcium per serving, because the body can absorb the calcium from milk easier than from other sources and because milk has lots of other important vitamins the body needs, including vitamin D."
A 1994 panel of experts convened by the National Institutes of Health to study optimal calcium intake also concluded that "the preferred source of calcium is through calcium-rich foods such as dairy products," Alexander said.
Both the Office of Women's Health and the U.S. Department of Agriculture have also joined the fight. Through "Team Nutrition," USDA provides nutrition curricula to schools that highlight the importance of calcium-rich foods. "Your SELF" is another USDA effort designed to get middle-school children to eat more calcium-rich foods.
Even with these efforts, experts say it is still a tough battle to increase calcium consumption. Just as science is finding more links between calcium intake and health, "people are eating less calcium," McCarron said. "It's a very disturbing pattern."
More information about Milk Matters! can be found on the Web at: www.nih.gov/nichd/docs/MILK/why_milk_matters.htm.
Age Recommended, Milligrams per day
0 to 6 months 210
6-12 months 270
1- 3 years 500
4-8 years 800
9-18 years 1,300
19-50 years 1,000
51 and older 1,200
NOTE: The Institute of Medicine/National Academy of Sciences also recommends that calcium intake not exceed 2,500 milligrams/day for those 1 year and older.
SOURCE: Institute of Medicine/National Academy of Sciences, 1997 Dietary Reference Intakes for Calcium, Phosophorus, Magnesium, Vitamin D and Fluoride
Calcium Content of Popular Foods
Here is a list of popular foods with their calcium content, along with the calories and fat content of each.
Nonfat (skim) milk, 8 ounces
Less than 1
Yogurt, plain, nonfat, 1 cup
Less than 1
Salmon, canned sockeye, drained with bone, 3 oz.
Broccoli, boiled, drained, 1/2 cup
Less than 1
Cottage cheese, 2% milkfat, 4 oz.
Cheddar cheese, 1 oz.
Ice cream, light, 50% fat, vanilla, 1/2 cup
Ice cream, chocolate, 1/2 cup
Milk shake, thick chocolate, 10.6 oz.
Pizza with cheese, 1 slice
Tofu, extra firm, nigari, 1/5 block
Tums E-X, 2 tablets
Viactiv, 1 chocolate chew
Less than 1
SOURCES: U.S. Department of Agriculture; Mead Johnson Nutritionals; Smithkine Beecham