Risk factors

Risk factors for osteoporotic fracture can be split between non-modifiable and (potentially) modifiable. In addition, there are specific diseases and disorders in which osteoporosis is a recognized complication. Medication use is theoretically modifiable, although in many cases the use of medication that increases osteoporosis risk is unavoidable.

Nonmodifiable

The most important risk factors for osteoporosis are advanced age (in both men and women) and female sex; estrogen deficiency following menopause is correlated with a rapid reduction in bone mineral density, while in men a decrease in testosterone levels has a comparable (but less pronounced) effect. While osteoporosis occurs in people from all ethnic groups, European or Asian ancestry predisposes for osteoporosis.Those with a family history of fracture or osteoporosis are at an increased risk; the heritability of the fracture as well as low bone mineral density are relatively high, ranging from 25 to 80 percent. There are at least 30 genes associated with the development of osteoporosis.Those who have already had a fracture are at least twice as likely to have another fracture compared to someone of the same age and sex.

Potentially modifiable

  • Excess alcohol - small amounts of alcohol do not increase osteoporosis risk and may even be beneficial, but chronic heavy drinking (alcohol intake greater than 2 units/day), especially at a younger age, increases risk significantly.
  • Vitamin D deficiency - low circulating Vitamin D is common among the elderly worldwide. Mild vitamin D insufficiency is associated with increased Parathyroid Hormone (PTH) production. PTH increases bone resorption, leading to bone loss. A positive association exists between serum 1,25-dihydroxycholecalciferol levels and bone mineral density, while PTH is negatively associated with bone mineral density.
  • Tobacco smoking - tobacco smoking inhibits the activity of osteoblasts, and is an independent risk factor for osteoporosis. Smoking also results in increased breakdown of exogenous estrogen, lower body weight and earlier menopause, all of which contribute to lower bone mineral density.
  • Low body mass index - being overweight protects against osteoporosis, either by increasing load or through the hormone leptin.
  • Malnutrition - low dietary calcium intake, low dietary intake of vitamins K and C Also low protein intake is associated with lower peak bone mass during adolescence and lower bone mineral density in elderly populations.
  • Physical inactivity - bone remodeling occurs in response to physical stress. Weight bearing exercise can increase peak bone mass achieved in adolescence. In adults, physical activity helps maintain bone mass, and can increase it by 1 or 2%. Conversely, physical inactivity can lead to significant bone loss.
  • Excess physical activity - excessive exercise can lead to constant damages to the bones which can cause exhaustion of the structures as described above. There are numerous examples of marathon runners who developed severe osteoporosis later in life. In women, heavy exercise can lead to decreased estrogen levels, which predisposes to osteoporosis. In addition, intensive training without proper compensatory increased nutrition increases the risk.
  • Heavy metals - a strong association between cadmium, lead and bone disease has been established. Low level exposure to cadmium is associated with an increased loss of bone mineral density readily in both genders, leading to pain and increased risk of fractures, especially in the elderly and in females. Higher cadmium exposure results in osteomalacia (softening of the bone).
  • Soft drinks - some studies indicate that soft drinks (many of which contain phosphoric acid) may increase risk of osteoporosis; Others suggest soft drinks may displace calcium-containing drinks from the diet rather than directly causing osteoporosis.
  • Caffeine – contrary to popular belief, there is no evidence linking caffeine to osteoporosis.

Diseases and disorders

Many diseases and disorders have been associated with osteoporosis. For some, the underlying mechanism influencing the bone metabolism is straight-forward, whereas for others the causes are multiple or unknown.

  • In general, immobilization causes bone loss (following the 'use it or lose it' rule). For example, localized osteoporosis can occur after prolonged immobilization of a fractured limb in a cast. This is also more common in active patients with a high bone turn-over (for example, athletes). Other examples include bone loss during space flight or in people who are bedridden or wheelchair-bound for various reasons.
  • Hypogonadal states can cause secondary osteoporosis. These include Turner syndrome, Klinefelter syndrome, Kallmann syndrome, anorexia nervosa, andropause, hypothalamic amenorrhea or hyperprolactinemia. In females, the effect of hypogonadism is mediated by estrogen deficiency. It can appear as early menopause (<45 years) or from prolonged premenopausal amenorrhea (>1 year). A bilateral oophorectomy (surgical removal of the ovaries) or a premature ovarian failure cause deficient estrogen production. In males, testosterone deficiency is the cause (for example, andropause or after surgical removal of the testes).
  • Endocrine disorders that can induce bone loss include Cushing's syndrome, hyperparathyroidism, thyrotoxicosis, hypothyroidism, diabetes mellitus type 1 and 2, acromegaly and adrenal insufficiency. In pregnancy and lactation, there can be a reversible bone loss.
  • Malnutrition, parenteral nutrition and malabsorption can lead to osteoporosis. Nutritional and gastrointestinal disorders that can predispose to osteoporosis include coeliac disease, Crohn's disease, lactose intolerance, surgery (after gastrectomy, intestinal bypass surgery or bowel resection) and severe liver disease (especially primary biliary cirrhosis). Patients with bulimia can also develop osteoporosis. Those with an otherwise adequate calcium intake can develop osteoporosis due to the inability to absorb calcium and/or vitamin D. Other micro-nutrients such as vitamin K or vitamin B12 deficiency may also contribute.
  • Patients with rheumatologic disorders like rheumatoid arthritis, ankylosing spondylitis, systemic lupus erythematosus and polyarticular juvenile idiopathic arthritis are at increased risk of osteoporosis, either as part of their disease or because of other risk factors (notably corticosteroid therapy). Systemic diseases such as amyloidosis and sarcoidosis can also lead to osteoporosis.
  • Renal insufficiency can lead to osteodystrophy.
  • Hematologic disorders linked to osteoporosis are multiple myeloma and other monoclonal gammopathies, lymphoma and leukemia, mastocytosis, hemophilia, sickle-cell disease and thalassemia.
  • Several inherited disorders have been linked to osteoporosis. These include osteogenesis imperfecta , Marfan syndrome, hemochromatosis, hypophosphatasia, glycogen storage diseases, homocystinuria, Ehlers-Danlos syndrome, porphyria, Menkes' syndrome, epidermolysis bullosa and Gaucher's disease.
  • People with scoliosis of unknown cause also have a higher risk of osteoporosis. Bone loss can be a feature of complex regional pain syndrome. It is also more frequent in people with Parkinson's disease and chronic obstructive pulmonary disease.

Medication

Certain medications have been associated with an increase in osteoporosis risk; only steroids and anticonvulsants are classically associated, but evidence is emerging with regard to other drugs.

  • Steroid-induced osteoporosis (SIOP) arises due to use of glucocorticoids - analogous to Cushing's syndrome and involving mainly the axial skeleton. The synthetic glucocorticoid prescription drug prednisone is a main candidate after prolonged intake. Some professional guidelines recommend prophylaxis in patients who take the equivalent of more than 30 mg hydrocortisone (7.5 mg of prednisolone), especially when this is in excess of three months. Alternate day use may not prevent this complication.
  • Barbiturates, phenytoin and some other enzyme-inducing antiepileptics - these probably accelerate the metabolism of vitamin D.
  • L-Thyroxine over-replacement may contribute to osteoporosis, in a similar fashion as thyrotoxicosis does. This can be relevant in subclinical hypothyroidism.
  • Several drugs induce hypogonadism, for example aromatase inhibitors used in breast cancer, methotrexate and other anti-metabolite drugs, depot progesterone and gonadotropin-releasing hormone agonists.
  • Anticoagulants - long-term use of heparin is associated with a decrease in bone density, and warfarin (and related coumarins) have been linked with an increased risk in osteoporotic fracture in long-term use.
  • Proton pump inhibitors - these drugs inhibit the production of stomach acid; it is thought that this interferes with calcium absorption. Chronic phosphate binding may also occur with aluminium-containing antacids.
  • Thiazolidinediones (used for diabetes) - rosiglitazone and possibly pioglitazone, inhibitors of PPARγ, have been linked with an increased risk of osteoporosis and fracture.
  • Chronic lithium therapy has been associated with osteoporosis.

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