The medical term for low bone density is osteopenia. Osteoporosis is an extreme form of osteopenia. Bone density or bone mass is determined by the amount of mineral content in the bones. Calcium, magnesium and phosphorus are major bone minerals. Genetic variables, diet, climate, medications and general health are some of the factors that determine bone density. Marked decrease in bone density causes bone weakness and vulnerability to fractures. Diminished bone density can be detected via DEXA scan, or dual energy x-ray absorptiometry, which determines bone density by calculating the amound of x-rays absorbed by bone.
Inadequate Vitamin D
According to "Harrison's Principles of Internal Medicine," inadequate intake of calories, protein and minerals during growth can compromise formation of peak bone mass and predispose to low bone density or osteoporosis later in life. Calcium metabolism is greatly affected by vitamin D. Dark skinned people and people who live in northern latitudes with diminished sunlight exposure can have inadequate amounts of vitamin D. Chronic kidney disease impairs vitamin D synthesis, which adversely affects calcium absorption and favors low bone density. Low calcium intake and inadequate vitamin D can be remedied by dietary adjustments and supplements containing vitamin D and calcium.
Senile and Post-menopausal Osteoporosis
Senile and postmenopausal osteoporosis are the most common causes of osteoporosis. For both men and women, bone mass naturally decreases with age. The term "senile osteoporosis" refers to bone loss that occurs with age. According to the University of Washington Department of Radiology, men begin to lose bone mass in the fifth and sixth decades of life. It is estimated that men lose .4 percent of bone mass per year after age 50.
Post menopausal osteoporosis overlaps with senile osteoporosis. For women, bone loss accelerates after menopause. Women lose .75 to 1 percent of their skeletal mass after age 35. After menopause, the rate of bone loss increases to as much as 2 to 3 percent per year. Bone loss can remain asymptomatic for many years. Bone loss may manifest clinically as low back pain, stress fractures of the foot, loss of height and "dowager's hump."
In the U.S., it is estimated that there are approximately 1 million bone fractures per year among post-menopausal women. Thirty percent of these fractures could be prevented if osteoporosis was eliminated. University of Washington Department of Radiology recommends exercise, calcium and vitamin D supplements, and avoidance of tobacco and alcohol as measures to combat osteoporosis.
Disuse Osteoporosis
Gravity plays a key role in the maintenance of skeletal integrity. Increased calcium excretion due to bone resorption occurs after a single day of bed rest. After prolonged periods of being immobilized, bone loss can be severe. Demineralization of bone caused by weightlessness is a health issue for astronauts and a challenge for space medicine.
References
- "Harrison's Principles of Internal Medicine"; Anthony S. Fauci, M.D., et al. (eds.); 2008
- About Anti-Ageing: What Causes Low Bone Density?
- University of Washington Department of Radiology: Osteopenia
- Steinberg Diagnostic Medical Imaging Centers: Dexa Scan
