Osteoporosis

Definition
Osteoporosis is defined as an absolute decrease in the amount of bone mass such that bones become fragile and porous. Bone is constantly remodeling as a normal process over the course of a lifetime. Bone is constantly breaking down and rebuilding in both the cortical (dense, hard) bones and the trabecular (cancellous – vertebrae) bones. Osteoporosis occurs when bone breaks down much faster than new bone is being formed –break down leads to decreased bone density and a greater than normal susceptibility to fractures.

Symptoms
Osteoporosis is often asymptomatic. Early symptoms are acute pain in the middle to low back; restricted spinal movement. Vertebral compression fractures and fractures of the femur (large leg bone), hip or arm can also be seen. In severe osteoporosis a characteristic Dowager’s hump may be seen.

Risk Factors
Post menopausal, premature menopause, amennorhea (estrogen is protective)
White or Asian ancestry, positive family history
Short stature, small bones, leanness
Low Calcium intake, high protein intake
Inactivity, disuse
Nulliparity (having no children, pregnancy increases bone mass)
Hyperparathyroidsim, thyroid disease
Gastric or small bowel resection
Overuse of antacids
Long term use of glucocorticoids
Smoking, heavy alcohol use, caffeine

Physiology
Bone is the hardest tissue in the human body. It functions to:
–support the fleshy structures.
–protect vital organs.
–contain bone marrow (blood cells are made here).
–act as a system of levers that allow movement based on muscle contractions.

Bone tissue is made of an intercellular calcified matrix with embedded cells that make and breakdown bone in a continuous cycle. Each bone has an external and internal lining of connective tissue that act to nourish the bone tissue. Calcium, phosphate, bicarbonate, citrate, magnesium, potassium and sodium are all present in bone. Calcium and phosphate combine to form a strong crystalline substance called hydroxyapatite that lies along collagen fibers in the matrix. The association of hydroxyapatite with collagen is responsible for the hardness and resistance of bone. 99% of total body calcium is located in bone and teeth; most is locked in the hydroxyapatite reservoir. Some calcium within bone is freely exchangeable with that in the blood such that it is available to the tissues to maintain normal function. Calcium in the blood must be tightly controlled because it is necessary to cell function for such things as blood clotting, muscle contraction, enzyme reactions, cellular communication and skin differentiation.

Calcium is rather deficient in the environment. The body has developed special mechanisms to extract calcium from dietary sources. Normal adults adapt to decreased calcium intake by increasing the fraction of dietary calcium absorbed, but absorption is impaired by aging. Several hormones are involved in calcium metabolism. Two protein hormones, parathyroid hormone and calcitonin, and a derivative of Vitamin D act to make sure the body optimally assimilates dietary calcium. Calcitonin is available as a therapy for osteoporosis where it helps to maintain the bone that is still present.

Nutrition
Dietary sources of calcium are mostly from the dairy foods. However, meat, some beans, seafood, tofu, and green leafy vegetables contain substantial amounts of calcium. 72% of the calcium available from dietary sources is from the dairy group. All women over 35 should see that they get enough calcium, magnesium, vitamins C & D and exercise. Unless an individual has an adverse reaction to milk’s components (e.g., lactose intolerance) milk consumption is encouraged.

Dietary Sources of Calcium
The following chart gives information about the approximate calcium content in a specified serving size for the following foods. This is intended to be a representative example of foods containing calcium, not a comprehensive source. Getting calcium in a well balanced diet is an excellent way to ensure bone health.

Calcium Supplements
Calcium supplements vary widely in terms of the amount of actual elemental calcium they contain. The table below is designed to serve as a guideline on the relative percentages of the various calcium products.

Calcium carbonate is inexpensive and provides the most elemental calcium per tablet, but it requires gastric acid for absorption so people with low gastric acid (the elderly or people taking blocking drugs for ulcer treatment) should take another form such as calcium citrate. Taking calcium supplements with food, especially acidic foods such as citrus,  increases calcium absorption.

Prevention
Things you can do to decrease your risk of osteoporosis — (Bone mass peaks at age 30-35):
Maintain a regular diet in calcium and protein.
Exercise (weight bearing exercise, gravity is our friend in this case)
Stop cigarette smoking (always an excellent health-promoting idea!)
Reduce alcohol intake
Avoid caffeine and overuse of carbonated beverages
Increase overall calcium intake to recommended levels:

RDA is at least 1100mg/day for adult women
RDA is 1600 mg/day for those age 11 to 24 and for pregnant or breastfeeding women.
U.S. – NIH recommends 1500 mg/day for women 19-24, pregnant or nursing and 1000-1500 for all other age groups.

*RDA = recommended daily allowance
**NIH = National Institutes of Health

Therapy
Drug therapy for osteoporosis is divided into three categories:
1. Agents that stimulate bone formation — none of these are approved by the FDA for treatment of osteoporosis.

a. Fluoride — increases bone mass. Mechanism still under investigation.
b. Parathyroid hormone — investigations show some potential, but not much information available on it in the treatment of osteoporosis.

2. Drugs that inhibit the breakdown of bones.

a. Bisphosphates (e.g., alendronate, Fosamax®) are absorbed onto the surface of the bone and protect the bone from being further broken down. In clinical trials, they are proven to be effective and are approved by the FDA. Side effects include gastrointestinal upset. It may also increase the incidence of esophogeal ulceration. May also experience some abdominal and muscle or bone pain. This drug tends to not be as effective if taken with food. Patients are advised to take it with a full glass of water on an empty stomach.
b. Calcitonin is normally produced in the thyroid gland and stops the breakdown of bone. It reduces the risk for new vertebral fractures and also provides some pain relief. It is approved by the FDA and is available as an injection or as a nasal spray. Minimal side effects include nausea, flushing and nasal ulcerations from the nasal spray. There is a possibility of an allergic reaction.

3. Hormone replacement therapy (HRT).

a. Estrogen has been shown to provide definite benefits against osteoporosis by stimulating the replacement of bone and inhibiting the breakdown. Estrogen regimens can be any of the following:

i. Continuous combination –estrogen + progesterone — this can cause some menstrual spotting for the first 3-6 months, then no more menstrual cycles.
ii. Continuous estrogen + cyclic progesterone
iii. Cyclic estrogen + progesterone

The FDA has recently approved an existing transdermal estrogen patch for the prevention of postmenopausal osteoporosis. The patch, delivers estradiol, is applied twice weekly, and has been available for the treatment of menopausal symptoms since1996.

b. Progesterone is used if the patient has an intact uterus — without the progesterone component, a patient with an intact uterus taking just estrogen has an increased risk of endometrial cancer.

c. Selective Estrogen Receptor Modulators (SERMs) — an option for someone who can’t or won’t take an estrogen. Has the same positive, anti-osteoporotic and cardioprotective effects as estrogen without causing the side effects associated with starting estrogen replacement therapy.