The keys to good bone health

We might think that our skeleton became an inert, fixed structure once we finished growing. But it’s quite the opposite! Every day, our bones adapt to our body’s immediate needs, adjusting their mass and shape.

Our bones continuously renew themselves throughout our lifetime. Two types of cells play a role, one after the other. First, osteoclasts remove (resorb) a small part of the bones to be renewed. Then, osteoblasts fill the vacant space by forming new bone. This succession of phenomena – resorption followed by bone formation – is called bone remodelling.

Several proteins and other elements are essential to the composition of our bones. First, there are amino acids, which produce collagen. This protein accounts for one-third of the bone structure and gives it its particular shape, whether it is a flat bone or a vertebra, for example. Then, calcium, phosphorus and small amounts of magnesium make up the remaining two-thirds of our bones. These minerals make them very strong. Vitamin D is essential, because it enables calcium absorption in our intestines and is involved in bone formation. Other proteins are also involved, such as osteocalcin, which helps deposit calcium in the bones with the help of vitamin K.

Estrogen plays a key role by decreasing osteoclast activity. This is in large part why osteoporosis is so common in women after menopause. In men, a small amount of estrogen is produced from testosterone. The gradual decline in testosterone levels with age is a lot slower in men, which explains in part why osteoporosis affects men less often.

Remodeling of a specific portion of bone is triggered by the physical stress it undergoes. When we exercise, we apply new loads to our bones, which stimulate the production of denser and stronger bone tissue.

Bone remodelling also explains why astronauts rapidly lose bone mass in the weightless environment of space. On Earth, our bones have to resist gravity to support our body weight. In space, this stress disappears: osteoclasts continue to resorb, but because osteoblasts are less active, they produce less new bone. Result: astronauts can lose 1% to 2% of their bone mass every month [4].

Osteopenia is defined as mild to moderate bone loss, whereas osteoporosis refers to more severe bone loss. When this bone fragility results in fractures, it is referred to as fracture osteoporosis. Osteoporosis progresses without symptoms for a long time. It is only when it is well advanced that we may have back pain, notice that we are shorter or experience fractures.

The main risk factor of osteoporosis is age [5]. More than 6% of the Canadian population has been diagnosed with osteoporosis, 81% of whom are women.

Other risk factors include [6]:

• genetics, particularly with certain forms of familial osteoporosis;
• low bone mass in early adulthood;
• long-term treatment with high-dose corticosteroids, including those used for rheumatoid arthritis and Crohn’s disease, as well as anti-ulcer medications and certain antidepressants;
• menopause and certain treatments that lower estrogen and testosterone levels, such as breast or prostate cancer treatments and surgical removal of the ovaries or testicles;
• overactive thyroid gland or parathyroid glands;
• a diet poor in calcium and vitamin D or malabsorption of these nutrients, as well as a lack of sun exposure;
• being too thin, lack of physical activity or prolonged immobilization;
• alcohol and tobacco use.

In the absence of fragility fractures, osteoporosis is primarily diagnosed through a bone density scan. This technique uses low-dose X-rays to measure bone mineral density (BMD). The severity of the condition is determined by comparing the patient’s BMD with that of a reference group of young adults of the same sex.

The results are expressed as a T-score.

• A T-score equal or less than -2.5 is strongly suggestive of osteoporosis.
• A T-score between -1.0 and -2.5 is classified as osteopenia.
• A T-score higher than -1.0 is considered normal.

Standard X-rays remain essential for diagnosing bone fractures that may complicate osteoporosis.

Some factors responsible for osteoporosis are out of our control such as genetics, gender, age or certain medications. However, a number of risk factors depend on our daily lifestyle choices:

• Adopting a balanced diet with sufficient calcium, vitamin D and vitamin K;
• Not smoking and limiting alcohol consumption;
• Exercising regularly;
• Preventing falls, especially for the elderly. In addition to these measures, there are medications available to treat the most severe forms of osteoporosis including bone resorption inhibitors such as bisphosphonates or bone formation agents.

Bone density loss is part of the natural aging process. However, a major part of prevention comes into play early in our lives. During childhood and adolescence, we build most of our bone mass, which will remain with us throughout our lives.

It is important to maintain these good habits as long as possible while limiting our alcohol consumption and quitting smoking. If there are warning signs – height loss, back pain, fractures from relatively mild impacts – we shouldn’t hesitate to consult a healthcare professional. They will prescribe a bone density test to guide prevention or treatment [7].