Basics about Bones and Bone Density Loss
You might expect that bone would be a straightforward thing to understand. You may think it is just that hard stuff keeping you from being a blob of jelly. Not so! Bone is involved with metabolism, producing immune system cells, and more. Although this lens cannot give you a complete medical education about bone and bone density loss, it is a solid introduction. Your bones are constantly being taken apart and re-made. On most occasions when those two activities get out of balance, the rebuilding gets slower than the destruction. Gradually, this results in loss of bone. Why does this happen, and what can be done about it?
The Bone Cycle
Bone is Continuously Destroyed and Rebuilt
Besides giving you a hard skeleton, your bones serve as a reservoir. Your body uses calcium for ongoing processes such as metabolism. When more calcium is needed in the bloodstream, some bone is destroyed to free the needed calcium. Later, the destroyed bone is rebuilt. This means your bones are constantly being taken apart and refreshed.
Two kinds of cells carry out this demolition and reconstruction:
- osteoclasts which destroy bone (a process called resorption), and
- osteoblasts which then build new bone at sites that have had some bone destroyed
You can keep these cells straight by remembering that the word "osteoblasts" contains the letter "b" for "build."
Hormones are Master Controllers
Something has to manage those cells. If you suspect the body uses one of its favorite tools for a lot of that, you're right–hormones are in the driver's seat.
Estrogen is perhaps the hormone most deeply entangled with the bone cycle. It:
- makes the body produce a molecule that slows down resorption–this molecule essentially gets in the way of bone destruction, preventing cells from getting a signal to turn into bone-destroying osteoclasts
- reduces production of another chemical that is involved in creating more bone-destroying cells
- encourages bone-destroyers to die, and
- helps bone-building osteoblasts live longer
This is apparently why so many women lose so much bone, starting near menopause. With lower estrogen levels, osteoblasts (builders) die quicker and osteoclasts (destroyers) live longer.
Other hormones that substantially affect bone formation and resorption include
- parathyroid hormone
- growth hormone, and
- insulinlike growth factor 1
Levels of growth hormone and insulinlike growth factor 1 are highest during puberty. That establishes your bone composition as you enter adulthood.
Parathyroid hormone (PTH) ordinarily does the opposite of the first portion of what estrogen does–it accelerates destruction of bone. When PTH is elevated for a long time, bone destruction gets out of control. This is why PTH levels must be checked in patients who experience bone density loss. (Click here to go to a page about parathyroid glands, what they do, and what can happen when they malfunction.)
Insulinlike growth factor 1 (IGF-1) provokes creation of more osteoblasts, causing more bone-building. The Framingham Heart Study correlated high IGF-1 levels with high bone density in women. Your serum level of IGF-1 is mostly heredity, although malnutrition can make it drop off dramatically. Of course, there is a trade-off. High IGF-1 helps protect against osteoporosis, but it is associated with a higher risk of cancer in the breast, colon or prostate.
The exact role of growth hormone (GH) is not fully understood, but it works in conjunction with IGF-1. Studies indicate that the GH/IGF-1 axis plays a regulatory role bone regeneration. It is particularly important for men with idiopathic osteoporosis.
The Basic Bone Cycle In Sequence
Here is the basic control mechanism in sequence. This is beneath the overall control settings established by estrogen:
- A drop in calcium levels in the bloodstream happens. This can occur because there isn't enough calcium in the diet, or because there isn't enough vitamin D to pull calcium from food.
- The parathyroid notices and secretes more PTH.
- The increased PTH level causes some bone to be destroyed, releasing calcium that the body needs to be able to pull from the bloodstream for metabolism.
- PTH also stimulates IGF-1, which orders more osteoblasts to be provided.
- By the time the osteoblasts are ready, the bone destruction (a quick task) is finished and it is time for replenishment of the destroyed bone (a slow task) to begin.
If the two aspects of bone utilization (destruction and rebuilding) get out of balance, over time you end up with the wrong amount of bone.
In childhood and early adulthood, your body tends to create bone faster than it destroys it. About 85% to 90% of bone mass is created by the age of 18 for women and 20 for men.
As you grow older, the balance tilts toward more bone destruction. If you are female, as you approach menopause, your hormone levels shift especially emphatically and can make the tilt toward destruction more dramatic.
When the balance is not corrected, this results in osteopenia (moderately low bone density) and then osteoporosis (so much bone loss that the risk of fractures is abnormally high). Something can go wrong with your bone cycle at any age. Although bone density loss is most common in older people, such things as a parathyroid problem can cause it to happen even when you are young.
Commonplace Risk Factors
- Being female
- Being older
- Personal history or family history of osteoporosis or (easily) broken bones
- Being small and thin
- Low sex hormone levels
- Low estrogen levels in women, regardless of whether due to menopause
- Missing periods (amenorrhea)
- Low levels of testosterone and estrogen in men
- Diet (a few specifics are included later in this list)
- Insufficient calcium intake
- Insufficient vitamin D intake (by getting a little exposure to sunshine or by taking supplements)
- Excessive intake of protein, sodium (usually from table salt) and caffeine (coffee, tea, etc.)
- Inactive lifestyle
- Three or more alcoholic drinks a day
- Some medications such as steroids, some anticonvulsants and others
- Some diseases and conditions such as anorexia nervosa, rheumatoid arthritis, and gastrointestinal diseases
Special Note about Carbonated Soft Drinks (Cola)
Many people say that consuming carbonated soft drinks destroys bone. Studies suggest they are both right and wrong about that.
The most persuasive and well run study I have seen on this topic so far found that drinking dark colored diet carbonated soft drinks (such as diet Coca Cola or diet Pepsi) leads to a loss of bone density in women. The effect can be startlingly high–as much as a 5% bone density loss from daily consumption of the equivalent of a couple of full-sized cans.
But this effect was not found in men, or with consumption of clear carbonated soft drinks, or with colored carbonated regular (not diet) soft drinks.
The study was only able to pin down this association, not the exact reason for it. Keep an eye on Medscape if you need to keep track of further developments yourself.
Detecting Bone Loss
Bone loss is a silent problem until it has become severe enough to cause real trouble. Many people do not realize they have osteoporosis until the day stepping off a curb is all it takes to break a hip, or picking up a bag of groceries it all it takes to fracture a vertebra.
To catch bone loss early enough to prevent trouble, you need to medical tests. In the USA, at a health fair, without a prescription, you can get a screening test cheaply (maybe $20 to $50). This is usually done on the back of a heel or perhaps the elbow. It does not hurt.
Since it is only a screening test, it is not very accurate. If screening results are not good, your doctor may want a proper Bone Mineral Density (BMD) scan. Medicare will generally reimburse for a BMD test every two years. BMD is a more expensive test (maybe $500, plus or minus some) that scans much of your body, with emphasis on the spine and hips.
The neck of the femur is the spot where bone density loss tends to show up first. That is also the most frequently troublesome spot. It takes a pounding all the time and breaks easily when it gets too weak. You can see on the scan image why that spot is so vulnerable. When you "break your hip," the break is usually at the neck of the femur.
Experts prefer a type of BMD that uses central dual energy x-ray absorptiometry (DXA). My doctor also recommends having any follow-up bone density scans in later years done on the same machine. Variations in calibration from one machine to another can disguise a trend in your bone density if your scans are done on different machines.
If you are a woman, when you go into perimenopause in the last years before menopause, a doctor who believes in preventive care may want a bone density scan even if screening tests look okay. Most people believe bone density loss does not become a big problem for women until menopause. That is not true. A large percentage of a woman's lifetime bone loss can occur in the three to five years immediately preceding menopause. That is in addition to a loss of up to 20% in the few years immediately after menopause.
Even if screening tests do not show an alarming rate of bone loss, current recommendations say women age 65 or older should get a bone scan at least once.
Who Should Be Tested?
According to the National Osteoporosis Foundation, the following groups should be tested for possible bone density loss:
- all postmenopausal women under the age of 65 with one or more risk factors (in addition to postmenopausal status)
- all women over the age of 65
- postmenopausal women or aging men who present with fractures, especially of the hip or spine
- women considering treatment for osteoporosis if findings would affect their decision-making
- women who have been on hormone replacement therapy (HRT) for extended periods of time, so that additional drug therapy can be added if HRT is not adequately protecting against bone loss
Risk factors that may also warrant screening include:
- women with a weight of less than 127 pounds (57.6 kg)
- family history of a fracture
- current cigarette smoking
- patients taking glucocorticoids or anticonvulsant drugs
- patients with medical conditions that may affect bone mass
Of course, if you have risk factors on the more extensive list earlier in this page, getting the inexpensive screening test once in a while would be prudent!
What if Your Scan Shows Bone Loss?
When the scan is not good, that indicates a problem, but it does not pin down why the problem is happening. Before deciding what to do, your doctor must figure out why the problem is happening.
Your doctor will run a serum calcium test to see whether a normal amount of calcium is available in your bloodstream. Low serum calcium levels trigger destruction of bone to release calcium.
Typically, a doctor will test parathyroid levels. Remember, an overactive parathyroid causes bone loss. If that is the reason for your bone loss, the malfunctioning parathyroid will probably be surgically removed, leaving your other parathyroid glands in place.
The doctor can also test whether your body is making use of the calcium you consume, or flushing a lot of it out of your system unused. If your body is not using the calcium you eat, the unused portion is excreted.
Next, there are tests of bone turnover. Bone turnover tests check how fast resorption and rebuilding of bone are being done, and whether they are in balance with each other.
Non-Prescription Treatment Options
The first line of treatment is adequate calcium intake and appropriate exercise. (Not all types of exercise help you build more bone.)
Intake of Calcium and Other Relevant Substances
- Young children need 400 to 800 mg/day of calcium.
- During the primary bone-formation years, appropriate daily intake is 1300 mg.
- It should be boosted to as much as 1600 mg/day during pregnancy.
- From young adulthood until near menopause, the need drops to 1000 mg of calcium daily.
- As a woman approaches menopause, needed intake rises to 1500 mg/day.
Calcium intake should be accompanied by proportional amounts of Vitamin D and magnesium because those are necessary for calcium utilization.
Your doctor may recommend higher intake levels for you if you are at risk for, or show signs of, calcium depletion. High doses should not be taken without a doctor's approval. Consuming much more calcium than your body uses can put you at risk for kidney stones.
If you take supplements, calcium citrate is preferable to calcium carbonate, even though the former is slightly more expensive. Calcium citrate is more readily absorbed and used by the body. It is also gentler to the stomach, and less inclined to cause gas, constipation or bloating.
Calcium carbonate supplements are frequently made from powdered oyster shell. In the USA, a substantial proportion of supplements made in that manner (up to 25% in one study) contain lead as a contaminant because the oysters absorbed it from their environment. Manufacturers are not currently required to mention any such lead contamination on their labels.
Proper utilization of calcium requires adequate levels of vitamin D and magnesium. You can buy calcium supplements that include appropriate amounts of vitamin D. It is best to take calcium supplements separately from ferrous (iron) supplements and multivitamins that contain iron, because iron interferes with calcium absorption.
Weight bearing exercise aids in the rebuilding of bone. Other types of exercise do not. The amount of weight borne during exercise need not be great. If you walk, you can swing a weight in each hand while you walk. If you go to a gym, you can do weight training with the lowest weight settings on the machines. You need not become a power lifter!
Even among weight bearing exercises, some are better than others for building your bones. For example, one study indicates that step training is more effective than classic resistance weight training at bone building for your all-important hips and legs.
Although diet and exercise are essential to preventing bone loss, recent studies indicate up to 70% of the variation in bone mass from person to person is due to heredity. Diet and exercise will help even when the genes are biased toward bone loss, but medication may be necessary.
Medicines for Treating Bone Loss
For many people, boosting calcium intake and weight bearing exercise still leaves bone loss occurring. In that case, drugs are needed in addition to adequate intake of calcium, Vitamin D and magnesium to fend off osteoporosis.
Most of the drug treatments are intended for use after menopause and cannot be used if there is any possibility of pregnancy occurring.
If your doctor prescribes drug therapy to help you maintain bone density, it is imperative that you also make sure your calcium intake at least meets the recommended daily requirement for your age. According to the 2001-2002 Physician Drug and Diagnosis Audit, only about one quarter of physicians mention that to patients for whom they prescribe an osteoporosis drug, even though the drug labels emphasize that they must be accompanied by adequate calcium intake.
Hormone Replacement Therapy
Since the July 2002 bombshell about the risks of hormone replacement therapy (HRT) outweighing the benefits, classic HRT is no longer recommended. Estrogen seems to be especially potent for bone retention, but postmenopausal women are generally supposed to try treatments other than estrogen replacement to treat their bone loss, and only resort to HRT if needed.
The full impact of estrogen is only beginning to be appreciated. A new class of synthetic mimics are being developed to provide the benefits of estrogen without the risks. At some point, those mimics may take the place HRT once held as a recommended option. Until then, other drugs must do the job.
Selective estrogen receptor modulators (SERMS) such as Evista® do not provide as much benefit for bone retention as estrogen for increasing bone density. SERMS can cause hot flashes. But Evista® does a neat trick of acting like estrogen in some tissues while blocking estrogen in other tissues. This may be why Evista® reduces the risk of breast cancer.
Antiresorptive Therapy: Bisphosphonates
Bisphosphonates are considered the strongest currently approved drugs for this purpose. Two leading varieties are Fosamax® (alendronate sodium) and Actonel® (risedronate sodium). They are antiresorptives, interfering with bone destruction in the constant bone regeneration process. These tablets tend to be hard on the digestive tract, but can be taken in weekly rather than daily doses. These drugs are approved by the FDA for preventing or treating osteoporosis in postmenopausal women and in men, including treatment of osteoporosis caused by long term use of steroid medications.
Boniva® (ibandronate) is approved for preventing or treating osteoporosis in postmenopausal women.
Reclast® (zoledronic acid) is approved to treat osteoporosis in postmenopausal women, to increase bone mass in men with osteoporosis, and to prevent new clinical fractures in patients who recently had a low-trauma hip fracture.
Didronel® (etidronate), is primarily used to treat Paget's Disease, or to address specific bone problems that can occur after hip replacement or spinal injury.
Many people cannot tolerate the orally administered bisphosphonates. In that case, intravenous bisphosphonates may be prescribed. Zometa® (zoledronic acid) is administered in a single dose or perhaps one dose per year. Aredia® (pamidronate) is also used for this purpose, but off-label, with doses every three months.
Antiresorptive Therapy: Other Medications
Miacalcin® (calcitonin-salmon) is a nasal spray. It is intended for use only by women more than five years beyond menopause who are not taking any type of estrogen-related therapy.
Fortical® is a different formulation of calcitonin.
Like the bisphosphenates, these are believed to reduce osteoclast activity and thereby reduce bone destruction. They can be used to treat osteoporosis in women who are at least five years beyond menopause. These drugs may need to be kept refrigerated between uses.
Bone Building Anabolic Therapy
Oddly, when PTH is only intermittently boosted via injections, bone density and structural integrity increase–especially in the spine. Daily injectable PTH was approved by the USA FDA late in 2002 as an osteoporosis treatment. The drug is Forteo® (teriparatide). It comes with a special warning because it causes malignant bone tumors in lab rats, and clinical trials on humans so far have only included a relatively limited number of people (in the low thousands).
This "pulsed PTH" treatment helps bone building osteoblasts live longer. It also activates insulinlike growth factor 1 (IGF-1), which in turn stimulates formation of more osteoblasts. Notice that this treatment boosts bone formation, where most of the other favored treatments reduce bone destruction.
Forteo® can be prescribed along with one of the other treatments to achieve better results by simultaneously affecting both sides of the bone regeneration process. The FDA recommends that this drug should not be used by a patient for more than two years.
Other Drug Therapies
Preliminary studies indicate that low dose treatment with human growth hormone can cause an increase in IGF-1 levels and can slow down the loss of bone density in postmenopausal women over the long term. In men, the effect on bone density may not be positive but the effect on mechanical strength of bone appears beneficial. In both women and men, the initial response to treatment increases the rate of both resorption and formation. As treatment continues, the resorption rate tends to return to its normal level, while in women the formation rate remains elevated.
Research to Watch
Statin drugs point toward a possibility for the future. Statins and bisphosphenates do similar things with the same biochemical pathways. The difference is that statins target liver cells, while bisphosphenates target bone cells.
Statins mostly get taken up by the liver very quickly, so very little has a chance to affect bone. Lovastatin and a newer drug called cerivastatin (atorvastatin) seem to have more effect on bone than the other statin drugs. It appears that:
- If you take a bisphosphonate and a statin, the combination can wipe out the bone retention effects of the bisphosphonate. Unless the drugs and dosages are carefully chosen, you can only use one or the other.
- Statins are capable of having the same effect on bone density as bisphosphonates, if only they could get to (and into) the bone cells.
- Statins don't just "lower cholesterol." They also have an anti-inflammatory effect, which may be the reason they reduce the incidence of heart attack and stroke. If there was a way to have some of a statin dosage go to bone and some to the liver, one drug could do all that plus help prevent bone density loss.
- If it is true that much of the trouble in some diseases comes from an overly active inflammatory process, a statin drug should also dampen some of that excess. It could therefore have health benefits for some patients beyond what it has for the general population.
Such applications of statin drugs are not ready for clinical use, but future developments may be worth watching.
Drugs with Adverse or Mixed Effects
Some non-steroidal anti-inflammatory drugs (NSAIDS) may either interfere with osteoblast production or cause osteoblasts to die prematurely. Other NSAIDS may prevent bone loss. Very different results are being found, depending upon exactly which NSAID is being used, at what dosage and for what duration.
- Proprionic NSAIDs might prevent bone loss is special situations. Those drugs include ibuprofen, naproxen, and ketoprofen.
- Acetic acid NSAIDs might not, and low dose aspirin apparently does not. Those include indomethacin and diclofenac.
- Ketorolac is blamed for an elevated rate of failure of spinal fusions.
But none of that is cast in stone yet.
The summary above does not show how much variation is turning up in study results as researchers try to figure out exactly what is going on and how dosage is involved. For example, PubMed's summary only says indomethacin does not prevent bone loss. A contradictory study done in Taiwan found that both indomethacin and ketorolac halt osteoblast production at a specific step (G0/G1 phase). The Taiwan study also found cytotoxic effects from diclofenac and piroxicam.
Similarly, other researchers have found that ibuprofen and indomethacin may interfere with the healing of fractures in long bones–yet ibuprofen is on the list of NSAIDS that the PubMed survey names as appearing to prevent bone loss.
The whole story about NSAIDS and osteoblasts apparently has not been put together yet. Perhaps the effect of NSAIDS on bone regeneration depends upon the patient's genetics in relation to calcium metabolism, or some other factor that has yet to be uncovered.
Bones and Electricity
Bone is a Piezoelectric Substance
This is an overview of some findings that may be of use if you are having trouble maintaining bone density. This is an offshoot of decades of investigation into EMFs (electromagnetic fields) and health.
Electricity and magnetism go together; an electric field generates a magnetic one and vice versa. We usually hear about electromagnetic fields (EMFs) in connection with concern about possible detrimental effects from high voltage power lines, building wiring, televisions, computer displays, and such.
But EMFs can also be used in medicine. During the 1950s, experiments began to show that bone is a piezoelectric substance. That means a change of shape such as bending creates local electric currents. Bend a piece of bone in a dark room, and you may see tiny sparks of light from it where the bending occurs.
This helped explain why exercise strengthens bone and being immobile weakens it, and brought to light the connection between subtle electric currents and bone growth. From there, using electric currents for therapy was a logical next step.
The USA FDA has approved EMF generators for a couple of medical uses. These devices are often used when bone fractures are refusing to heal, and to fuse spinal vertebrae in people with unrelenting back pain. If the piezoelectric traits of bone help to activate bone building, that may also help to explain a study which found step training more effective for bone building than classic resistance weight training.
Research into medical application of EMFs has begun to look at more complex problems than bone density and healing stubborn fractures. Several years ago, Brown University School of Medicine in Providence RI tried EMFs to treat a strain of guinea pigs that usually start showing signs of osteoarthritis by the time they are 1 year old. One group of research animals got EMF therapy for 6 months starting at an age of 1 year. The other group got no treatment. At the end of the study, a few of the treated animals seemed to have no pain, and most had relatively mild disease. The untreated animals all had crippling osteoarthritis. The results were so dramatic that the study was repeated to make certain it was correct before publication; results came out the same.
This is not quite the same as the result of earlier bone treatments. It not only reduced swelling and pain, it modified development of the disease. There are some experimental indications that the EMF treatment is increasing production of natural anti-inflammatory agents in the joints.
There are also experiments underway with regard to possible EMF treatment of soft tissue (e.g. to reduce swelling in the wrists of carpal tunnel syndrome patients).
Caution: The research done so far, and the devices approved so far, make it clear that properly applied EMFs can be effective therapeutically. However, that does not mean all EMFs are necessarily good. Just as a drug can be misused, so can this. An EMF therapeutic device that has no solid, specific research behind it (to tune the frequency of the vibrations, the strength of the electric current, etc) might ultimately turn out to be just as big a gamble as a new drug that has not been through formal scrutiny and approval. The safest way to get to this type of treatment right now for osteoporosis or osteoarthritis would be to try to get into a clinical trial if/when they start trying it on people, and hope that the researchers are far enough along for the trial to do you some good.
National Osteoporosis Foundation: This link will take you directly to the NOF web page that provides clinical guidelines. If you want the official word about diagnosis and treatment, go here!
- Davidson, Michele R. "Pharmacotherapeutics for Osteoporosis Prevention and Treatment." Journal of Midwifery and Women's Health, volume 48, 2003.
- Rosen, Clifford J. "Restoring Aging Bones." Scientific American, Feb 2003. ( www.sciam.com ) Solid introductory article.
- Sugimoto T; Kaji H; Nakaoka D; Yamauchi M; Yano S; Sugishita T; Baylink DJ; Mohan S; Chihara K. "Effect of low-dose of recombinant human growth hormone on bone metabolism in elderly women with osteoporosis." European Journal of Endocrinology, Sep 2002.
- Watts, Nelson (MD). "Bisphosphenates, Statins, Osteoporosis, and Atherosclerosis." Southern Medical Journal, July 2002. (http://www.medscape.com/viewarticle/438222)
Special thanks go to the National Osteoporosis Foundation for the extensive and very up-to-date information available through its website at www.nof.org
I am not a medical professional. Years ago I was a volunteer sysop in an online forum for people with chronic illnesses. The forum was so highly regarded that some doctors sent patients to it to learn how to live with their illnesses. I did a fair amount of translating from medical jargon into something more understandable for the benefit of the forum's members. If you need a detailed and completely up-to-the-minute understanding of this topic, please consult the original medical literature. I'm no substitute for that!
Some Relevant Books
The Whole-Body Approach to Osteoporosis: How to Improve Bone Strength and Reduce Your Fracture Risk (The New Harbinger Whole-Body Healing Series)
The Osteoporosis Diet: The Complete Guide To Osteoporosis Nutrition, Supplements, & Exercise To Reverse Bone Loss Without Drugs
Your Bones: How You Can Prevent Osteoporosis and Have Strong Bones for Life – Naturally
Dr. Lani’s No-Nonsense Bone Health Guide: The Truth About Density Testing, Osteoporosis Drugs, and Building Bone Quality at Any Age
The Wellness Doctor’s Guide to Preventing and Reversing Osteoporosis (The Wellness Doctor Series Book 1)
Before You Comment
I reject comments that just attempt to get people to sign on with an ambulance-chasing law firm to file malpractice lawsuits.
Yes, Fosamax can have severe side effects for some people. Yes, some defective artificial joints have gotten produced and implanted in some people. Every powerful medication and treatment can have bad consequences for some patients. Using such drugs or treatments is always a matter of trade-offs.
I welcome legitimate information and feedback but I do not welcome unbalanced comments that attempt to scare people into any particular course of action. I also do not welcome comments that just briefly compliment the page in order to post one or two unrelated spammy links.
Each person's situation is unique and individual. This page is intended to promote understanding of the bone cycle so everyone can make well-informed decisions about their own personal care. Please honor that goal–your help toward that goal is very welcome.