Osteoporosis – Pathophysiology
Osteoporosis causes bones to become weak and brittle — so brittle that a fall or even mild stresses like bending over or coughing can cause a fracture. Osteoporosis-related fractures most commonly occur in the hip, wrist or spine.
Bone is living tissue that is constantly being broken down and replaced. Osteoporosis occurs when the creation of new bone doesn’t keep up with the removal of old bone.
Osteoporosis affects men and women of all races. But white and Asian women — especially older women who are past menopause — are at highest risk. Medications, healthy diet and weight-bearing exercise can help prevent bone loss or strengthen already weak bones.
There typically are no symptoms in the early stages of bone loss. But once bones have been weakened by osteoporosis, you may have signs and symptoms that include:
- Back pain, caused by a fractured or collapsed vertebra
- Loss of height over time
- A stooped posture
- A bone fracture that occurs much more easily than expected
Your bones are in a constant state of renewal — new bone is made and old bone is broken down. When you’re young, your body makes new bone faster than it breaks down old bone and your bone mass increases. Most people reach their peak bone mass by their early 20s. As people age, bone mass is lost faster than it’s created.
How likely you are to develop osteoporosis depends partly on how much bone mass you attained in your youth. The higher your peak bone mass, the more bone you have “in the bank” and the less likely you are to develop osteoporosis as you age.
A number of factors can increase the likelihood that you’ll develop osteoporosis — including your age, race, lifestyle choices, and medical conditions and treatments.
Some risk factors for osteoporosis are out of your control, including:
- Your sex. Women are much more likely to develop osteoporosis than are men.
- Age. The older you get, the greater your risk of osteoporosis.
- Race. You’re at greatest risk of osteoporosis if you’re white or of Asian descent.
- Family history. Having a parent or sibling with osteoporosis puts you at greater risk, especially if your mother or father experienced a hip fracture.
- Body frame size. Men and women who have small body frames tend to have a higher risk because they may have less bone mass to draw from as they age.
Osteoporosis is more common in people who have too much or too little of certain hormones in their bodies. Examples include:
- Sex hormones. Lowered sex hormone levels tend to weaken bone. The reduction of estrogen levels at menopause is one of the strongest risk factors for developing osteoporosis. Women may also experience a drop in estrogen during certain cancer treatments. Men experience a gradual reduction in testosterone levels as they age. And some treatments for prostate cancer reduce testosterone levels in men.
- Thyroid problems. Too much thyroid hormone can cause bone loss. This can occur if your thyroid is overactive or if you take too much thyroid hormone medication to treat an underactive thyroid.
- Other glands. Osteoporosis has also been associated with overactive parathyroid and adrenal glands.
Osteoporosis is more likely to occur in people who have:
- Low calcium intake. A lifelong lack of calcium plays a major role in the development of osteoporosis. Low calcium intake contributes to diminished bone density, early bone loss and an increased risk of fractures.
- Eating disorders. People who have anorexia are at higher risk of osteoporosis. Low food intake can reduce the number of calories and amount of protein and calcium ingested. In women, anorexia can stop menstruation, leading to weaker bones. In men, anorexia lowers the amount of sex hormones in the body and can weaken bone.
- Gastrointestinal surgery. A reduction in the size of your stomach or a bypass or removal of part of the intestine limits the amount of surface area available to absorb nutrients, including calcium.
Steroids and other medications
Long-term use of oral or injected corticosteroid medications, such as prednisone and cortisone, interferes with the bone-rebuilding process. Osteoporosis has also been associated with medications used to combat or prevent:
- Gastric reflux
- Transplant rejection
Some bad habits can increase your risk of osteoporosis. Examples include:
- Sedentary lifestyle. People who spend a lot of time sitting have a higher risk of osteoporosis than do those who are more active. Any weight-bearing exercise and activities that promote balance and good posture are beneficial for your bones, but walking, running, jumping, dancing and weightlifting seem particularly helpful.
- Excessive alcohol consumption. Regular consumption of more than two alcoholic drinks a day increases your risk of osteoporosis.
- Tobacco use. The exact role tobacco plays in osteoporosis isn’t clearly understood, but it has been shown that tobacco use contributes to weak bones.
Bone fractures, particularly in the spine or hip, are the most serious complication of osteoporosis. Hip fractures often result from a fall and can result in disability and even death from postoperative complications, especially in older adults.
In some cases, spinal fractures can occur even if you haven’t fallen. The bones that make up your spine (vertebrae) can weaken to the point that they may crumple, which can result in back pain, lost height and a hunched forward posture.
Tests and diagnosis
Your bone density can be measured by a machine that uses low levels of X-rays to determine the proportion of mineral in your bones. During this painless test, you lie on a padded table as a scanner passes over your body. In most cases, only a few bones are checked — usually in the hip, wrist and spine.
Treatments and drugs
Treatment recommendations are based on an estimate of your risk of breaking a bone in the next 10 years using information such as the bone density test. If the risk is not high, treatment might not include medication and might focus instead on lifestyle, safety and modifying risk factors for bone loss.
For both men and women at increased risk of fracture, the most widely prescribed osteoporosis medications are bisphosphonates. Examples include:
- Alendronate (Fosamax)
- Risedronate (Actonel, Atelvia)
- Ibandronate (Boniva)
- Zoledronic acid (Reclast)
Side effects include nausea, abdominal pain, difficulty swallowing, and the risk of an inflamed esophagus or esophageal ulcers. These are less likely to occur if the medicine is taken properly. Intravenous forms of bisphosphonates don’t cause stomach upset. And it may be easier to schedule a quarterly or yearly injection than to remember to take a weekly or monthly pill, but it can be more costly to do so.
Using bisphosphonate therapy for more than five years has been linked to a rare problem in which the middle of the thighbone cracks and might even break completely. Bisphosphonates also have the potential to affect the jawbone. Osteonecrosis of the jaw is a rare condition that can occur after a tooth extraction in which a section of jawbone dies and deteriorates. You should have a recent dental examination before starting bisphosphonates.
Estrogen, especially when started soon after menopause, can help maintain bone density. However, estrogen therapy can increase a woman’s risk of blood clots, endometrial cancer, breast cancer and possibly heart disease. Therefore, estrogen is typically used for bone health only if menopausal symptoms also require treatment.
Raloxifene (Evista) mimics estrogen’s beneficial effects on bone density in postmenopausal women, without some of the risks associated with estrogen. Taking this drug may also reduce the risk of some types of breast cancer. Hot flashes are a common side effect. Raloxifene also may increase your risk of blood clots.
In men, osteoporosis may be linked with a gradual age-related decline in testosterone levels. Testosterone replacement therapy can help increase bone density, but osteoporosis medications have been better studied in men with osteoporosis and are recommended alone or in addition to testosterone.
Other osteoporosis medications
If you can’t tolerate the more common treatments for osteoporosis — or if they don’t work well enough — your doctor might suggest trying:
- Denosumab (Prolia). Compared with bisphosphonates, denosumab produces similar or better bone density results and reduces the chance of all types of fractures. Denosumab is delivered via a shot under the skin every six months. The most common side effects are back and muscle pain.
- Teriparatide (Forteo). This powerful drug is similar to parathyroid hormone and stimulates new bone growth. It’s given by injection under the skin. After two years of treatment with teriparatide, another osteoporosis drug is taken to maintain the new bone growth. This drug is reserved for patients with severe osteoporosis.
Lifestyle and home remedies
These suggestions may help reduce your risk of developing osteoporosis or experiencing broken bones:
- Don’t smoke. Smoking increases rates of bone loss and the chance of experiencing a fracture.
- Avoid excessive alcohol.Consuming more than two alcoholic drinks a day may decrease bone formation. Being under the influence also can increase your risk of falling.
- Prevent falls. Wear low-heeled shoes with nonslip soles and check your house for electrical cords, area rugs and slippery surfaces that might cause you to trip or fall. Keep rooms brightly lit, install grab bars just inside and outside your shower door, and make sure you can get into and out of your bed easily.
Video: Medical Nucleus Media
Article: Mayo Clinic