Bone is constructed from calcium and other minerals crystallized on a soft matrix (a sort of 3-D frame) of collagen and other proteins. The combination of organic and inorganic materials makes bone both rigid and strong. (Unlike calcium alone—think of how easy it is to snap a piece of chalk, which is made primarily of calcium, in half.) Blood vessels run throughout bone. In the center of each bone you find marrow, where blood cells are made.
Your skeleton is made of two kinds of bone. About 80 percent of it is cortical bone, which is hard, dense, and stiff. It makes up the outer shell of most bones, and the long bones in your arms and legs, and most of your hip bones. It is designed to withstand quite a bit of stress. Spongy trabecular bone is found inside of cortical casings, in the vertebrae, at the ends of the long bones in your limbs, and in parts of your hips.
As bones age, cells called osteoclasts seek out old or damaged parts of the bone and dissolve them, which is called resorption. Resorption dissolves crystallized calcium and other minerals in your bones, returning them to the blood. This leaves small spaces, and cells called osteoblasts create new bone to fill them in. In forming new bone, calcium and other minerals are taken from the blood and crystallized in the bone. The continuous cycle of formation and breakdown is known as bone remodeling. When all goes well, this is a constant tit-for-tat for many years, with the osteoblasts (builders) staying just ahead of the osteoclasts (dissolvers) to produce bone that is growing and getting denser—or maintaining good density.
You lose and gain bone this way throughout your lifetime. Remodeling is orchestrated by various hormones, and in later chapters you will see how important maintaining natural levels of hormones is to the health of your bones. Throughout childhood and into young adulthood, bone formation outpaces resorption, so you get taller as your bones get longer, for one thing, and your bones also get wider and denser. But the neat teamwork of osteoblasts and osteoclasts comes uncoupled somewhere around age 35, and bone breakdown can then outpace bone formation— and that’s the rub. If the osteoclasts are busier dissolving bone than the osteoblasts are busy making it, your bones actually get holes in them. That’s osteoporosis—literally, porous bones. Thin bones like that are brittle and fragile, so they fracture easily. Osteoporotic fractures can cause disfiguration, chronic pain, immobility, and even death.
Officially, osteoporosis is divided into two categories. Type I, which is postmenopausal osteoporosis, mainly affects women between 50 and 65, and usually involves trabecular bone more than cortical bone. Type II, which is “age-associated,” and the bane of older people, typically involves loss of cortical bone equal to that of trabecular. Osteoporosis known to be caused by a medication or disease is known as secondary osteoporosis.
Osteomalacia, or soft bones, known as rickets in children, is a related concern, occurring when minerals don’t crystallize on the bone matrix properly (often due to lack of vitamin D, which you need to make use of the calcium, phosphorus, and magnesium— not to mention vitamins A and E). With osteomalacia, you don’t have enough calcium and phosphorus forming into bone, but that alone is not the same as osteoporosis. Osteoporosis involves lack of other minerals as well, along with a decrease in bone matrix. For healthy bones, both bone mass and bone quality are key. Osteomalacia can be a precursor of osteoporosis.
Another precursor is osteopenia, which means simply low bone mass: density that is lower than normal, but not low enough to lead to fractures. This is a warning sign that osteoporosis— which does lead to a high rate of fractures—is on its way unless you take action. Far too often, the first sign of osteoporosis (or the first one that gets read, anyway) is a fracture that is spontaneous or results from a minor impact, especially in the hip, wrist, or spine. Most victims don’t even realize they are in danger until they are already at a crisis point. The second goal of this book, after prevention, is awareness. You won’t be able to protect yourself and keep yourself healthy unless you know you are at risk.
If you know their significance, there are other signs that your bones are already in trouble. Bad back pain, especially in the lower back, or other bone pain, is a common symptom, as is a decrease in height. Deformity is also a signal, particularly kyphosis—dowager’s hump or hunchback— resulting from multiple fractures in the vertebrae that cause the vertebrate to become wedged together and the spine to collapse. Several other signs, especially if clustered together, may be pointing toward osteoporosis: leg and foot cramps, especially at night, extreme fatigue, large amounts of plaque on the teeth, periodontal disease, loss of teeth, brittle or soft fingernails, premature graying, and heart palpitations. Especially in the case of these more amorphous associations, you should rule out everything else before you pin the cause on osteoporosis or low bone density. Don’t panic because you need your teeth cleaned more than every six months: you might just have a super-conscientious dentist, or need a better brushing/flossing routine, or you just have a lot of plaque.
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