Bone and Calcium Metabolism
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Prevention of Osteoporosis QuickTimeª and a
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By Dr. Murray Fox
Bone metabolism in the human body is a very dynamic process. There is a constant lying
down of bone by cells called osteoblasts and resorbtion of bone by cells called osteoclasts.
Initially the osteoblasts work much harder and faster that the osteoclasts and bone is laid
down to facilitate growth.
Each person has a genetically determined peak bone mass which is attained in their
twenties. By age 17 ninety percent of the bone mass has been obtained. The
consequence of bone loss is the development of very weak and fragile bones, a medical
condition known as osteoporosis. Osteoporosis is associated with compression fracture of
the bones of the spine called vertebra(ae) and fracture of the hip. While these fractures
from osteoporosis may be painful and cause shortening of stature, even difficulty
breathing, the major consequence is complications and even death from surgical repair of
the hip fracture.
Calcium and Vitamin D Play a Critical Role
Adequate calcium, exercise and vitamin D are required to attain and maintain bone
mass. This is important in the prevention of osteoporosis. Current data indicates that the
majority of children do not receive adequate amounts of calcium or vitamin D.
Recommended amount of calcium vary for individuals. Below is a table of adequate
intakes as outlined by the National Academy of Science.
Recommended Calcium Intakes
Ages Amount mg/day
Birth–6 months 210
6 months–1 year 270
1–3 500
4–8 800
9–13 1300
14–18 1300
19–30 1000

31–50 1000
51–70 1200
70 or older 1200
Pregnant & Lactating 1000
14–18 1300
19–50 1000
Vitamin D also plays an important role in healthy bone development. Vitamin D helps in
the absorption of calcium (this is why milk is fortified with vitamin D). In the past many
people depended on the sun’s effect on the skin to make vitamin D. Since more emphasis
has been place on sunscreen, there is less sun effect and a greater need for vitamin D
supplement. The exact amount of vitamin D required is being debated, but the
consensus is that Americans are generally deficient in vitamin D and require greater
amounts than originally thought. 800 international units to 1000 international units is the
current recommendation for adults.
Certain medical conditions may limit the amount of calcium that may be ingested. As
always, consulting your physician is suggested regarding your personal specific calcium
needs.
Exercise is Necessary to Maintain Bone Health
Weight bearing exercise (walking, running, etc.) is an excellent stimulus for bone growth.
Current recommendations are:
Adults: Engage in at least 30 minutes of moderate physical activity [on] most, preferably
all, days of the week
Children: Engage in at least 60 minutes of moderate physical activity [on] most,
preferably all, days of the week
Bone Mineral Density
The evaluation of bone strength, the about of calcium in the bone, is measured by a dual
density densitometer. The purpose of this is to measure the exact bone mineral density of
the spinal vertebrae, usually the four lumbar (lower back) vertebrae, and the femur, the
large thigh bone that connects to the pelvis in the hip socket.
The bone mineral density (BMD) is usually expressed as a “T” score which is a
comparison of the patients BMD to a young person. A “T” score that is - 1 or higher is
considered normal. A “T” score of - 2.5 or lower is considered osteoporosis. A “T” score
between – 1 and – 2.5 is called osteopenia – a softening of the bone.
Bone mineral density testing should be recommended to all postmenopausal women aged
65 years or older. Bone mineral density testing may be recommended to postmenopausal
women younger than 65 years who have 1 or more risk factors for osteoporosis (See

Below). Bone mineral density testing should be performed on all postmenopausal women
with fractures to confirm the diagnosis of osteoporosis and determine disease severity.
Risk Factors for Osteoporotic Fracture in Postmenopausal Women
• History of prior fracture
• Family history of osteoporosis
• Caucasian race
• Dementia
• Poor nutrition
• Smoking
• Low weight and body mass index
• Estrogen deficiency*
o Early menopause (age younger than 45 years) or bilateral oophorectomy
o Prolonged premenopausal amenorrhea (>1 year)
• Long-term low calcium intake
• Alcoholism
• Impaired eyesight despite adequate correction
• History of falls
• Inadequate physical activity
Dr. Murray Fox, MD
Women’s Specialists of Plano
3809 W 15th St # A
Plano, TX 75075
(972) 379-2416
www.obgynplano.com/dr-murray-fox