How does osteoporosis develop?

Bone is made up of calcium and other minerals, which make bone hard. Bone density, or bone mineral density, refers to the mineral content of the bones. It is related to how hard and strong they are. Low bone density is seen in osteoporosis.

Bone is a type of tissue. Like other tissues in the body, bone constantly repairs and renews itself. In bone, this process is called remodeling. Two kinds of cells carry out remodeling:

• Osteoclasts. Cells that break down, causing the resorption of bone and the release of calcium into the blood.

• Osteoblasts. Cells that draw calcium from the blood and create new bone.

A balance between the bone-building osteoblasts and bone-dissolving osteoclasts keeps bones healthy.

In young people, bones lengthen and increase in density. At about age 35, bones start to lose density and strength. Most cases of osteoporosis result from the speeding up of bone loss that can occur for a number of reasons:

• Lower levels of the hormones estrogen and testosterone in the body

• Lack of physical activity

• Too little calcium, vitamin D, or both

• Smoking

• Too much alcohol use

• Certain medicines such as steroids

Osteoporosis is more common in women than in men. This is because during menopause, a woman's ovaries greatly reduce the amount of estrogen made. Estrogen is a hormone that keeps the bone-dissolving activity of the osteoclasts in check. After menopause, the osteoblasts continue to build bone, but they can't keep up with the speed at which the osteoclasts break it down. If no measures are taken to prevent or slow bone loss, osteoporosis can occur.

Bone loss in men generally begins later and advances more slowly than it does in women. Men tend to have larger and stronger bones than women do. They also don't go through the sudden hormonal changes that occur with menopause. As men age, they do lose bone density, in part because of a natural decrease in testosterone. Men and women lose bone mass at similar rates by age 65 to 70. Calcium absorption, which is needed to keep bones healthy, also decreases in men and women.

How does cancer treatment affect bone loss?

Various cancer treatments can increase the risk for osteoporosis for both men and women. Some chemotherapy medicines used to treat breast cancer and various hormonal therapies for breast and prostate cancer can cause a loss of bone density. There are some ways to prevent and treat osteoporosis. Talk about these choices with your healthcare provider.

What causes osteoporosis in men with prostate cancer?

It is well known that testosterone and other male hormones called androgens can stimulate the growth of prostate cancer. For this reason, a common treatment for prostate cancer is to lower the level of testosterone in the body. This approach has been successful in treating men with prostate cancer that has spread throughout the body. Some healthcare providers may also use this treatment when the disease is diagnosed early, before it has spread beyond the prostate.

Low testosterone levels can slow prostate cancer growth. But they can also lead to loss of bone density in men. In particular, hormonal therapies that deprive the body of androgens increase the risk for osteoporosis. These androgen-deprivation therapies include:

• Orchiectomy. This surgery takes out the testicles, the main source of testosterone.

• Luteinizing hormone-releasing hormone analogs (agonists), or antagonists. Medicines, such as leuprolide, relugolix, and goserelin, lower testosterone levels in the body.

Can osteoporosis in men with prostate cancer be prevented or treated?

Not all men develop osteoporosis from androgen-deprivation therapy. But the treatment can increase the risk for this disease. So men getting it should consider having routine bone mineral density screenings. This type of X-ray can diagnose osteoporosis, detect low bone density, keep track of how well treatments are working, and predict the risk for future fractures. It is also called DEXA (dual energy X-ray absorptiometry).

Once bone is lost, it can't be completely replaced using current therapies. Osteoporosis can't be cured. But it can be slowed down. There are a number of ways to prevent and treat osteoporosis in men.

Lifestyle approaches for preventing bone loss in men include:

• Getting more calcium and vitamin D. Calcium comes from the food we eat. Dairy products (such as milk, yogurt, and cheese) and nondairy foods (like salmon, spinach, fortified juices, and tofu) are good sources. Vitamin D comes from diet (fish, eggs, and fortified foods like juice, milk, milk alternatives, and cereal) and the sun. For men older than 50, the recommended daily intake of calcium is 1,000 to 1,200 mg. For vitamin D, it's 600 to 800 international units. 

• Exercising. Regular physical activity, especially weight-bearing exercises, can help prevent bone loss. These include jogging, dancing, stair-climbing, and arm exercises.

• Not smoking

• Limiting how much alcohol you drink

Medical approaches for preventing and treating bone loss in men include:

• Bisphosphonates. Bisphosphonates are medicines that prevent the breakdown of bone. There are different types of bisphosphonates. Some are taken by mouth. Others are given by IV infusion. Two bisphosphonates are pamidronate and zoledronate. They are given as IV infusions. They can be used to treat prostate cancer that has spread to the bones. They may also help prevent osteoporosis in men during androgen-deprivation therapy for prostate cancer. Risedronate and alendronate are approved by the FDA for preventing and treating osteoporosis in men and women. Both medicines are available as pills.

• RANKL (receptor activator of nuclear factor kappa-B ligand) inhibitors.  These medicines work in a different way than bisphosphonates. Denosumab is approved by the FDA to treat osteoporosis. It is also approved to prevent bone loss caused by hormonal therapy given for the treatment of cancer, if used with calcium and vitamin D supplements. It is given as a shot.

• Calcitonin. Calcitonin is a naturally occurring hormone. It is important for calcium regulation and bone metabolism. It is often given as a nasal spray.