Like the steel supports of a large building, bone is the structural support of the body. Unlike steel, however, bone is alive. Bone can change in strength, density and shape, and how we care for our bones will influence our structural strength. The body does most of its bone building during the first 30 years of life. Bone is constantly being broken down and replaced, however, bone loss begins to outpace bone growth between the ages of 30 and 35. Although an adult's body doesn't build bone as effectively as it did in childhood, adults can still take steps to maintain bone strength. Bone depletion can be minimized through adequate calcium intake, weight-bearing exercise and hormone replacement therapy.
Strength to last a lifetime
Genetics determine our skeletal size and mass, and it's up to us to make the most of what nature has given us. Adequate calcium intake in childhood and adolescence is essential to attain optimal bone mass and size. Weight-bearing exercise is critical, too. A 1991 study from Indiana University showed a direct correlation between children's bone strength and their level of physical activity.
So while our bodies are programmed to give us a certain minimum or maximum bone strength, our choices in diet and exercise will determine our level of bone development within that genetically set range.
Bones consist of about 50 percent water and 50 percent solid matter, primarily calcium-containing salts. Made up of tough fibers, bone serves as a storage place for calcium and marrow.
Bone loss happens to all adults, but it proceeds faster in women. The decrease in bone mass in adulthood is caused primarily by a decrease in hormones, which regulate bone metabolism. The drop in hormone levels for post-menopausal women is dramatic; for men, the decrease is more gradual.
The only sure way to measure bone strength is through bone density testing, now widely available. The National Osteoporosis Foundation recommends bone density tests for all women over age 65 and postmenopausal women with fractures or one or more risk factors for osteoporosis.
Bone up on calcium
You've seen the commercials: "Milk builds strong bones." It's true, but apparently many people don't heed this advice. Most Americans don't consume even half of the recommended daily allowance (RDA) of calcium. The National Institutes of Health (NIGH) recommends between 1,000 and 1,500 milligrams of calcium a day for healthy adults; the average adult consumes only 500 to 700 milligrams of calcium a day.
The preferred source of calcium is food. Dairy products, such as milk, cheese and yogurt, are the best source of dietary calcium, although calcium can also be found in other foods, such as salmon (with bones), some legumes, tofu and green, leafy vegetables. Some chemical components in spinach and wheat bran may reduce the absorption of calcium.
Getting the RDA of calcium from food alone requires careful attention, so many physicians recommend calcium supplements. For the best absorption, take your supplement at mealtime and don't take more than 500 milligrams of calcium at one time. Calcium interferes with some drugs, so discuss your medications with your doctor or pharmacist.
You'll get more than a boost in bone strength from calcium. Studies have shown that calcium may play a protective role in a number of disorders, including gastrointestinal cancers, hypertension, preclampsia and colon cancer. The NIH has noted that people need not exceed the RDA for calcium to gain these benefits.
Weight bearing exercise strengthens bones
Using exercise to build strong bones isn't a new idea. In fact, it was first proposed in 1892 by a fellow named Wolff. Wolff's theory held that exercise strengthened bone as well as muscle, making bone less susceptible to fracture. In the century since, many studies have proven Wolff's theory to be true.
In fact, we now know that athletes have stronger bones than non-athletes; an increase in training is reflected in bone strength; and some sports provide more bone-building potential than others. Among athletes, weightlifters have the greatest bone density, while swimmers have the least bone density. That's because swimming is not a weight-bearing activity.
A weight-bearing exercise is one in which the bone has to support additional weight or force beyond its usual requirement, which is to support the weight of the body against gravity. The bones of a weightlifter not only need to support the weightlifter's body; the bones are also supporting the weight of the object being lifted. Swimmers' bones aren't supporting additional weight -- they don't even support the weight of the body, the water does.
You don't need to be a world-class weightlifter to develop strong bones through exercise. Walking, jogging, bicycling, tennis, basketball, soccer and dancing are all forms of weight-bearing exercise that will strengthen your bones.
Keep in mind that exercise is site specific. If your preferred form of exercise is walking, for example, you'll see the bone strength increase in your legs more so than in your arms. Of course, you can improve your results by carrying small handheld weights and swinging your arms when you walk.
Exercise also plays an important role in preventing falls. Bone density, muscle mass, strength and balance -- all benefits of exercise -- reduce the risk of falling. While increased calcium intake and hormone replacement therapy may help build strong bones, only weight-bearing exercise strengthens bone and diminishes the risk of falling.
Please note that if you already suffer from osteoporosis -- or you suspect that you may -- you should check with your doctor before beginning an exercise program.
Hormone replacement therapy proven successful
For people with -- or at risk for -- osteoporosis, medications are available that can slow bone loss, increase spinal bone density and help prevent fractures. These hormone replacement therapies inhibit the function of certain cells in the bone called osteoclasts. Osteoclasts work to remove excess bone tissue during bone growth or repair.
In women, estrogen therapy has been shown to prevent bone loss, reduce menopausal symptoms and decrease the risk of cardiovascular disease. However, it also presents a slight increase in the risk of breast and endometrial cancer.
As an alternative to estrogen therapy, a drug called raloxifene hydrochloride provides the same bone protection without increased risk of cancer. Another option is a nasal spray called calcitonin-salmon, which has been shown to increase spinal bone mass in women with established osteoporosis.
Finally, if you're at risk for osteoporosis, you need to discuss your level of risk and treatment options with your doctor. Together, you can determine a plan to help you build better bone strength.