Osteoporosis occurs when bones lose mass and density, which is partly a result of a decrease in calcium, phosphorus and other minerals. When this occurs, bone strength decreases and the bone’s internal supporting structure declines. Instead of being dense with interconnecting pieces, bone becomes porous and weak.

Scientists are unsure why this process occurs, although they do know that it is related to bone remodeling. This is the life-long process of creating new bone (formation) and breaking down old bone (resorption). The resorption and formation of bone are essential in repairing small fractures and replacing bone.

Bone remodeling takes two to three months to complete the cycle. Younger people generate new bone faster than old bone is broken down, causing bone mass to increase. By age 20, people have generally accumulated most of their bone mass. Bone mass peaks during the mid-30s. After that, more bone is lost during remodeling than is gained. Not exercising and not getting enough calcium (through diet) and vitamin D (through diet and sunshine) can accelerate the process.

When women reach menopause (change that occurs when a woman’s body no longer releases eggs), bone loss is accelerated even further. Bone loss related to menopause usually lasts for about 10 years. This continues until about age 60, when bone loss slows but does not stop. In contrast, men initially do not lose as much bone mass as they age. However, by age 65, men lose bone at the same rate as women. The risk of developing osteoporosis depends on the amount of bone mass developed between 25 and 35 and how rapidly it is lost during aging.

Several risk factors are associated with osteoporosis. These include:

• Sex and age. Fractures attributed to osteoporosis are more common in women than in men. This increased risk in women is due to the fact that they:
  
• • Tend to start out with lower bone mass
  • Tend to live longer than men
  • Experience a sudden drop in estrogen during menopause (either natural or surgical) which accelerates bone loss
    
    
  However, by age 65, men lose bone at the same rate as women. By age 75, osteoporosis is equally likely in both sexes. Osteoporosis will cause a hip fracture in 6 percent of men after age 50 and a vertebral fracture in 5 percent of that population, according to the National Institutes of Health (NIH).
  
  
• Race. People with fair skin, such as Caucasians and Asians, are most likely to experience osteoporosis. African-Americans and Hispanics have lower incidences, but risk remains fairly high.
  
  
• Family history. Osteoporosis runs in families, and a person’s risk increases if parents or siblings have the disease.
  
  
• Frame. People who are thin or have small body frames have less bone mass, which puts them at higher risk.
  
  
• Lifestyle factors. In addition to diet, these include:
  
• • Tobacco use. Researchers know that tobacco use weakens bones, although the exact relationship between tobacco use and osteoporosis is not clearly understood.
    
    
  • Sedentary lifestyle. Bone health begins in childhood and is strongly influenced by exercise. Exercise throughout life can increase bone density. Weight-bearing exercise, such as walking, aerobics or lifting dumbbells, is particularly beneficial in building bone mass.
    
    
  • Chronic alcoholism. Excess consumption of alcohol reduces bone formation and interferes with the body’s ability to absorb calcium. Among men, alcoholism is one of the greatest risk factors for osteoporosis.
    
    
• Hormones. Lifetime exposure to estrogen is a factor for women. Those who began menstruating at an earlier-than-normal age or who experience menopause later in life are at reduced risk for osteoporosis. However, women are at higher risk if they:
  
• • Have a history of absent menstrual periods (amenorrhea)
    
    
  • Experience menopause earlier than their 40s
    
    
  • Have their ovaries surgically removed before age 45 without receiving hormone replacement therapy (HRT)

For men, a low level of testosterone (male hypogonadism) is a risk factor for osteoporosis as well as insulin resistance, sexual dysfunction and other health problems. Testosterone levels decline as men age, and scientists have documented a rising incidence of male hypogonadism in recent decades. Below-normal levels of estrogen and estradiol in men may also promote osteoporosis.

• Eating disorders. A history of anorexia nervosa or bulimia in women and men elevates the risk of lower bone density in the lumbar spine and hips.
  
  
• Rheumatoid arthritis (RA) or juvenile rheumatoid arthritis. These chronic diseases of the joints can lead to pain, limited mobility and bone loss.
  
  
• Cardiovascular conditions. Studies have linked osteoporosis to disorders including coronary artery disease, heart attack, heart failure and stroke.
  
  
• Diabetes. Research indicates that type 1 diabetes and possibly type 2 diabetes, which is far more common, increase the risk of osteoporosis in men and women.
  
  
• Polycystic ovarian syndrome. An endocrine disorder that involves irregular menstrual cycles. The irregular estrogen levels associated with this condition may increase the risk of lower bone density.
  
  
• Other diseases. Additional disorders that raise the risk of osteoporosis include asthma, chronic obstructive pulmonary disease (COPD), gastrointestinal diseases including liver disease and inflammatory bowel disorders, kidney disease, hypercalciuria (excess calcium in the urine, a sign of kidney stones), neoplastic disease (e.g., cancer or benign tumors), ankylosing spondylitis, cystic fibrosis, homocysteinuria (high levels of an amino acid called homocysteine), a genetic bone disease called osteogenesis imperfecta and a rare cellular disorder called systemic mastocytosis, according to the NIH.
  
  
• Medications. Long-term use of some corticosteroids or other immunosuppressants damages bones. These medications are used to treat RA and other forms of arthritis, asthma, psoriasis, lupus and other chronic conditions. 

Intramuscular birth control medication has also shown to cause decrease in bone density, especially if used in teenagers.

Too much thyroid hormone can also cause bone loss. This may occur as a result of an overactive thyroid (hyperthyroidism) or when a person takes thyroid medication to treat an underactive thyroid (hypothyroidism). Blood tests can ensure that thyroid levels remain optimal.

Some diuretics can cause the kidneys to excrete excessive levels of calcium, which can contribute to thinning of bones. Diuretics are drugs that prevent the buildup of fluids in the body, and they are often used to treat high blood pressure.

Finally, hormonal treatment for prostate cancer, some anticoagulants, anticonvulsants and antacids containing aluminum have been shown to contribute to bone loss.

• Low calcium. In addition to lack of dietary calcium, medical procedures (such as stomach surgery) and medical conditions (such as Cushing’s disease, parathyroid disease and digestive disorders) that inhibit the absorption of calcium can also contribute to bone loss.
  
  
• Radiation therapy. Radiation treatment for cancers in the pelvic area may raise the risk of osteoporotic fractures.
  
  
• Stem cell therapy. A type of stem cell treatment called hematopoietic cell transplantation reduces bone mineral density in children and sometimes causes osteopenia (a type of bone weakness) or osteoporosis.
  
  
• Exposure to lead. The NIH is pursuing evidence that exposure to lead during childhood might limit bone development and predispose a person to osteoporosis later in life.
  
  
• Consumption of cola. Recent research from the Framingham Osteoporosis Study found drinking cola to be an independent risk factor for low hipbone mineral density in women.