Most Americans have heard the message: Post-menopausal women need plenty of calcium to maintain bone density and head off the effects of osteoporosis. For the same reason, men older than 50 -- who also are vulnerable to osteoporosis -- and younger women must be equally aware of the importance of building strong bones. So who else needs more calcium? The answer: everybody.
Calcium is the most abundant mineral in the human body, with 2 or 3 pounds stored in the bones and teeth of the average man or woman. It's crucial not only to building strong bones and teeth but also for contraction of blood vessels, nerves and muscles, and the regulation of blood pressure.
The body doesn't make calcium, and the majority of Americans -- whatever their age -- do note get enough through diet. According to the U.S. Report Health People 2000: The Surgeon General's Report on Health Promotion and Disease, calcium deficiency in this country is "serious enough to warrant national attention."
With the number of Americans diagnosed with osteoporosis increasing seven-fold during the past decade, the calcium message is usually aimed at women, and men, older than 50. But, according to the National Institutes of Health, only 13.5 percent of adolescent girls and 36.3 percent of boys get the recommended daily amount of calcium.
The primary dietary source of calcium is dairy foods -- milk, yogurt and cheese -- and three servings a day are needed. Adults may avoid these foods, because they are relatively high in fat and calories, and children and adolescents may choose soft drinks and fatty snacks.
The result is an increased risk of not only osteoporosis, but obesity, high blood pressure and a number of other medical problems.
Osteoporosis literally means "porous bones," and post-menopausal women are most at risk because of a decline in calcium absorption that occurs as a result of reduced estrogen production. Of the 10 million Americans with osteoporosis, 80 percent are women, but older men also are vulnerable to deteriorating bone mass and the resulting risk of fractures of the hip, vertebrae, wrist, pelvis, ribs and other bones.
The stage is typically set much earlier in childhood and adolescence when bones are growing. Adequate intake of calcium is crucial during youth not only to help bones grow to normal length but also to develop strength, density and mass to help counter the losses that may occur in later life.
Throughout life, bone goes through constant change, with small amounts of old bone being broken down (resorbed) and new bone formed through the deposition of calcium. During youth, ideally there is more formation than breakdown. Once peak bone mass is reached at about age 30, breakdown and deposition of bone remain roughly equal until age 50 or so, when breakdown may start to exceed new bone formation. This change may be because of a lower intake of calcium or, more likely, to decreased absorption that often accompanies aging.
When inadequate stores of calcium are available, the body digs into the bones to obtain the calcium needed to maintain normal nerve, muscle and blood vessel function.
The role of calcium in controlling blood pressure is becoming increasingly clear.
It's long been known that vegetarians who eat a diet high in minerals such as calcium, magnesium and potassium are less likely than others to develop high blood pressure.
More recently, the Dietary Approaches to Stop Hypertension diet, focusing on fruits, vegetables, whole grains and low-fat dairy products, has been found effective enough at lowering blood pressure that many subjects were able to reduce or discontinue their medication.
Researchers attributed improvements to the increased calcium obtained from reduced fat dairy products -- along with minerals, such as magnesium and potassium from the fruits and vegetables.
A later study found the DASH approach even more effective than sodium restriction in lowering blood pressure.
Although evidence is not yet conclusive, there are indications linking an increased calcium intake with a reduced risk of colon cancer. In one study, subjects taking 1200 milligrams daily of calcium carbonate had a reduced recurrence of pre-cancerous adenomas in the colon.
Another study found that colon cancer patients getting a similar amount of calcium from low-fat dairy products were less likely to have a recurrence of cancer.
Data from the Nurses' Health Study and Physicians' Health Study concluded that subjects consuming 700 to 800 milligrams a day of calcium were 40 percent to 50 percent less likely than other subjects to develop left side colon cancer.
According to other research, low levels of calcium in the diet tend to promote the storage of fat, conversely, a large intake of calcium leads to increased burning of fat.
Some believe that 1,200 to 1,600 milligrams of calcium a day, combined with moderate calorie restriction, may promote weight loss.
Calcium also has been associated with a reduced severity of premenstrual syndrome, a lower incidence of kidney stones and improved metabolism.
It's best, of course, to increase your calcium intake through foods such as low-fat dairy products or fortified orange juice, which have other nutrients needed to ensure maximum absorption.
Other sources include kale, Chinese cabbage, broccoli, beans, tofu and canned sardines and salmon (with the bones).
Vitamin D helps improve absorption of calcium.
Absorption is decreased, on the other hand, when too much calcium is consumed at one meal.
High intake of sodium and protein can increase excretion of calcium before it is absorbed.
A proper balance of calcium, magnesium and potassium may be as important of the actual amount of each nutrient consumed -- reinforcing the idea that it's better to get your nutrients through a variety of foods.
Some individuals -- such as post-menopausal, pregnant and breast-feeding women; vegans; and people with lactose intolerance -- may, however, need supplements.
The burgeoning incidence of osteoporosis in this country, serious enough on its own, should be taken as a sign that Americans of all ages -- women and men -- should eat more of this multi-purpose mineral.
It is estimated that the average American gets only about 600 milligrams a day -- less than half of what is required for healthy living.