Osteoporosis - causes; Low bone density - causes

Your body needs the minerals calcium and phosphate to make and keep healthy bones.

• During your life, your body continues to both reabsorb old bone and create new bone.
• As long as your body has a good balance of new and old bone, your bones will stay healthy and strong.
• Bone loss occurs when more old bone is reabsorbed than new bone is created.

Sometimes bone loss occurs without any known cause. Other times, bone loss and thin bones tend to run in families. In general, white women are the most likely to have bone loss.

Brittle, fragile bones can be caused by anything that makes your body destroy too much bone, or keeps your body from making enough bone.

Weak bones can break easily, even without an obvious injury.

As you age, your body may reabsorb calcium and phosphate from your bones instead of keeping these minerals in your bones. This makes your bones weaker. When this process reaches a certain stage, it is called osteoporosis.

Many times, a person will fracture a bone before they even know they have bone loss. By the time a fracture occurs, the bone loss is serious.

Women over age 50 and men over age 70 have a higher risk of osteoporosis than younger women and men.

• For women, a drop in estrogen at the time of menopause is a major cause of bone loss.
• For men, a drop in testosterone as they age can cause bone loss.

Your body needs calcium and vitamin D and enough exercise to build and keep strong bones.

Your body may not make enough new bone if:

• You do not eat enough high-calcium foods
• Your body does not absorb enough calcium from the foods you eat

Certain habits can affect your bones:

• Drinking alcohol. Too much alcohol can damage your bones. It can also put you at risk for falling and breaking a bone.
• Smoking. Men and women who smoke have weaker bones. Women who smoke after menopause have an even higher chance of fractures.

Younger women who do not have menstrual periods for a long time also have a higher risk of bone loss and osteoporosis.

Many long-term (chronic) medical conditions can keep a person confined to a bed or chair.

• This keeps the muscles and bones in their hips and spine from being used or bearing any weight.
• Not being able to walk or exercise may lead to bone loss and fractures.

Other medical conditions that may also lead to bone loss are:

• Rheumatoid arthritis
• Chronic kidney disease
• Overactive parathyroid gland

Sometimes, medicines that treat certain medical conditions can cause osteoporosis. Some of these are:

• Hormone-blocking treatments for prostate cancer or breast cancer
• Some medicines that are used to treat seizures or epilepsy
• Steroid medicines, if they are taken by mouth every day for more than 3 months

Any treatment or condition that causes calcium or vitamin D to be poorly absorbed can also lead to weak bones. Some of these are:

• Gastric bypass (weight-loss surgery)
• Cystic fibrosis
• Other conditions that prevent the small intestine from absorbing nutrients well

People with eating disorders, such as anorexia nervosa or bulimia, are also at higher risk for osteoporosis.

Talk to your health care provider about your risk for bone loss and osteoporosis. Find out how to get the right amount of calcium and vitamin D, what exercise or lifestyle changes you should do, and what medicines you may need to take.

Lewiecki EM. In the clinic. Osteoporosis. Ann Intern Med. 2011 Jul 5;155(1):ITC1-1-15; quiz ITC1-16.

National Osteoporosis Foundation. Clinician's Guide to Prevention and Treatment of Osteoporosis. Washington,DC: National Osteoporosis Foundation;2010.

Miller KK, et al. Determinants of skeletal loss and recovery in anorexia nervosa. J Clin Endocrinol Metab. 2006;91(8):2931-2937.