The thought of bones often conjures scenes from archaeological digs or a cemetery. Your bones, though, are living things made up of substances that are continually breaking down and being rebuilt. This process is known as remodeling.
Every year, 20 percent to 40 percent of your skeleton is renewed. Children’s bodies make new bone faster than they break down existing bone, which causes bone mass to increase. People reach their peak bone mass in their twenties.
However, in the late thirties, the body begins to break down more bone than it makes. This decrease is slight; normal bone loss is only about 0.3 percent to 0.5 percent per year. The result of this slow loss is that the skeleton becomes less dense and more fragile. The process accelerates the older you get. After menopause, women lose bone density at a rate of 2 percent to 4 percent every year. Men lose 1 percent to 2 percent after the age of sixty.
It goes without saying that if you are trying to ensure the health of your bones, the goal should be to build bone mass when you are young and to maintain it when you get past the age when bone remodeling is at its peak. If you do this, chances are you won’t have problems with your bones later in life. But if you don’t build bone mass when you are young, and if you lose bone mass at an excessive rate after the peak bone-building age, your bones can get more porous and brittle (osteoporosis, a painless disease), which means they can break more easily. If the bone-rebuilding process itself is compromised, you may have symptoms such as persistent pain and bone deformity (osteomalacia or rickets).
How can you build bone mass when you are young and maintain it when you are older? The answer to both questions is the same: be active and get enough calcium in your diet. When we emphasize calcium intake for bone health, the importance of vitamin D is often ignored. But vitamin D is like the yeast in a recipe for bread. You can’t make bone without vitamin D available. And it all starts in your parathyroid glands and intestine.
The opposing processes of bone resorption (the dissolving of existing bone tissue) and formation (the filling of the resulting small cavities with new bone tissue) are well regulated so that an adult’s total mass of bone tissue normally remains nearly constant, but it’s constantly being broken down and replaced such that 20 percent to 40 percent of an adult’s skeleton is remodeled every year. In an infant’s first year of life, almost 100 percent of his or her skeleton is replaced.
A number of factors affect bone development, growth, and repair, including hormones, exercise, and vitamin D synthesis. Vitamin D is necessary for proper
absorption of calcium in the small intestine, from which it can move to your skeleton via your bloodstream and be deposited in the bones to given them their strength—rather like a cement. When vitamin D is absent, calcium is poorly absorbed, which compromises the bone-remodeling process—not enough bone is made to replace the bone that is broken down. The constant breakdown and replacement of bone that occurs throughout your life is spurred largely by parathyroid hormone, which is released from your parathyroid glands, which sit on the upper and lower poles of your thyroid. Without enough calcium moving to your bones thanks to vitamin D’s presence, that delicate dance between bone breakdown and bone creation can become imbalanced. In other words, you can eat as much calcium-rich food, drink as much milk, and take as many calcium supplements as you want to, but if you don’t have enough vitamin D in your body, you won’t be able to effectively absorb that calcium for your bones. And you won’t be able to outpace the breakdown of bones, leading to serious bone-related conditions.
So why is calcium so critical? The intercellular collagen matrix of bone tissue needs a considerable amount of calcium hydroxyapatite to have normal bone mineralization. It is estimated that a person who is vitamin D deficient will absorb only about one third to one half as much calcium as he or she would with a healthy vitamin D status. Without enough vitamin D to help your bones absorb calcium—or without enough calcium itself—your bones don’t remodel properly.
This can happen at any age. And it’s not just about bone health. Low calcium absorption triggers a cascade of physiological problems, as calcium is important for most metabolic functions and neuromuscular activities.
Can Osteoporosis Be Averted Despite Advanced Age?
The most commonly known bone disease is osteoporosis, which is characterized by porous, brittle, and weak bones. Vitamin D deficiency can cause osteoporosis, and it can make it worse. Even when people are consuming enough calcium, numerous studies have shown that they still will not build and maintain bone mass if they are deficient in vitamin D. And even more studies have shown that people who suffer from osteoporosis often have vitamin D deficiency.
As I’ve been reiterating, not getting enough vitamin D doesn’t just affect your bones in old age. If you don’t get enough vitamin D during those early years
when it’s crucial to build bone mass—up until your thirties—you won’t establish the bone mass you need to keep your bones strong when you naturally break down more of the bone structure than you can make. Men do get osteoporosis, but women are at much greater risk. Because women have less testosterone, they have less muscle mass (this also explains why women have a harder time building and maintaining muscle mass, as testosterone factors heavily into one’s muscle mass). Women, in fact, start out with lower bone mass and tend to live longer; they also experience a sudden drop in estrogen at menopause that accelerates bone loss. At the beginning of menopause, women can lose as much as 3 percent to 4 percent of bone mass every year. Slender, small-framed women are particularly at risk. Men who have low levels of the male hormone testosterone are also at increased risk. Doctors can detect early signs of osteoporosis with a simple, painless bone density test (densitometry).
You are at especially high risk of vitamin D deficiency-related osteoporosis if you are predisposed to vitamin D deficiency. There is one exception when comparing the risks of vitamin D deficiency and osteoporosis. Although people of African descent living in higher latitudes are at higher risk of vitamin D deficiency because their bodies don’t convert sunlight into vitamin D as easily as races with fairer skin, they do not appear to be at a higher risk of osteoporosis than those with fairer skin. The reason for this is that people of African genetic lineage tend to start with 9 percent to 15 percent denser bones than Caucasian people. However, chronic vitamin D deficiency will overcome this natural protection and cause African Americans to suffer increased loss of bone density and risk of fracture.
An indication of the importance of vitamin D on the bone density of seniors was found in a study my colleagues and I did of senior citizens living in Maine, which showed that they lost 3 percent to 4 percent of their bone mass in the fall and winter and regained it in the spring and summer months. Obviously, the most serious problem associated with osteoporosis is fractures. As noted previously, osteoporosis is responsible for 1.5 million fractures each year, most notably fractures of the vertebrae (causing the hunched appearance often seen in elderly women and painful sciatica due to nerve compression in the lower back), ribs, wrists, and hips. Hip fractures tend to be crippling and are sometimes fatal.
Osteoporosis-related fractures are more common during the winter months, when muscles tend to be weaker and there’s an increased risk of falling. Unless a person remains active during the winter months, thus keeping up muscle mass and bone strength, there’s a greater likelihood of falling and breaking bones. A
vitamin D deficiency could worsen the situation, since UVB-absent winter months require adequate storage of vitamin D for use and vitamin D supplementation.
Because there is no pain until a fracture occurs, osteoporosis is known as the silent threat. Numerous studies have shown that vitamin D—usually in conjunction with calcium—is an effective treatment for increasing or maintaining bone density and preventing fractures associated with osteoporosis.
Finnish researchers found that 341 elderly people (mostly women ages seventy-five and older) who were given vitamin D injections experienced fewer fractures than 458 people who did not receive the supplements. A French study of 3,270 elderly women showed 43 percent fewer hip fractures in participants who were given an 800 IU vitamin D supplement every day and 800 milligrams of calcium than in those participants who were given a placebo. A study of a less high-risk group was done by Dr. Bess Dawson-Hughes and her colleagues in the Boston area when 391 men and women ages sixty-five and older were given either a 700 IU vitamin D supplement or a placebo. The results showed that the participants who were given the supplement sustained half as many fractures as the placebo group and experienced significant bone density increases.