Bones are organs that contain metabolically active tissues composed primarily of materials and a
fibrous protein called collagen. We have two types of bone: cortical and trabecular. Cortical bone
is dense and composes about 80% of our bone. Trabecular bone is porous in nature and
composes about 20% of our bone. Trabecular bone is more sensitive to hormonal and nutritional
factors and turns over more rapidly than cortical bone.
The three types of bone activity are growth, modelling and remodelling. Our bones reach their
peak bone mass by our late teenage years and into our twenties; bone mass begins to decline
around age 40. Bone is constantly being recycled through a process called remodeling.
Remodeling of bone involves the resorption of bone through the action of osteoclasts and the
formation of bone through the action of osteoblasts.
Dual energy x-ray absorptiometry (DXA or DEXA) is the gold standard measurement of bone
mass. It is a simple, safe and painless procedure. DXA can measure bone mass throughout the
entire body. The results if a DXA include a T-score, which is a comparison of you bone density
with that of a 30 year old healthy adult of the same sex and race. A T-score between +1 and -1 is
normal; a score between -1 and -2.5 indicates poor bone density; and a score more negative than
-2.5 indicates osteoporosis.
Quantitative ultrasound, peripheral dual energy x-ray absorptiometry, and single energy x-ray
absorptiometry are other methods that can be used to measure bone density. These methods
typically measure the bone density of peripheral sites such as the heel, wrist or finger.
Calcium is the most abundant mineral in our bodies. It is a significant component of our bones.
Blood calcium is maintained within a very narrow range, and we use our bone calcium to
maintain normal blood calcium if dietary intake is inadequate. Calcium is necessary for normal
nerve and muscle function. The AI for calcium is 1000 mg per day for adults aged 19 to 50; the
AI increases to 1200 mg per day for older adults and is 1300 mg per day for adolescents. Dairy
products, canned fish with bones, and some green leafy vegetables are good sources of calcium.
The most common long-term effect of inadequate calcium consumption is osteoporosis.
Hypercalcemia causes muscle and joint aches and mental confusion, while hypocalcemia causes
muscle spasms and convulsions.
Vitamin D is a fat-soluble vitamin and a hormone. Vitamin D can be made in our skin from
exposure to the sun. Vitamin D regulates intestinal calcium absorption and blood calcium levels
and maintains bone health. The AI for vitamin D is 5 µg (200 IU) per day for adult men and
women aged 19 to 50 years; the AI increases to 15 µg (600 IU) per day for adults over the age of
70 years. The UL for vitamin D is 50 µg (2000 IU) per day for all adults. Foods contain little
vitamin D, with fortified