Bone Health after Childhood Cancer
 

Friday, September 05, 2008

Bone Health after Childhood Cancer 
by Kevin Oeffinger MD and Nancy Keene

Treatment for childhood cancer sometimes damages the bones, causing an increased risk for developing osteoporosis (weak bones). Fortunately, there are several things survivors can do to strengthen their bones and avoid or minimize this problem. It is therefore important to find out if you are at risk and ensure that you get the appropriate testing and counseling so that any problems are identified early and treated.

Bone Mass (Strength) and Osteoporosis

First, let's talk about bones in general. In the next section, we will talk about bones in childhood cancer survivors. To start with, here are a few terms that will be used in this column:

Bone mineral density or bone mass = bone strength
Osteoporosis = weakened or brittle bones
Bone density test = test to determine the density or strength of the bone

Bone is a living, growing tissue. The human skeleton contains 206 bones, all held in place by connective tissues such as ligaments and tendons. The skeleton gives structure to the body and protects the internal organs. The skeleton also works as a factory, since the marrow in the bones manufactures various blood cells. Bones also act as a storage depot holding calcium and phosphorus for later use by the body.

Nearly half of the bone in an adult's body is created during adolescence. During the teen years, the length of bones increases. The density and mass of bone dramatically increase as well. The average person reaches their peak density or strength of their bones around the age 25 to 30. Then, as we age, calcium is slowly lost from our bones, causing them to weaken as we get older.

When a person's bones are significantly weakened or less dense (brittle bones), s/he is at a much higher risk for having a fracture (broken bone) of the hip, wrist, or other bones, from a simple fall. Also, the vertebrae (bones of the spine) can collapse or "smush" down, which makes the person shorter and can lead to a curvature of the spine. This often causes a lot of problems including chronic pain. This disease, osteoporosis (osteo = bone; porosis = porous), affects 10 million Americans. Another 18 million Americans are at risk and have low bone mass. Many of us have seen this disease in our grandparents, especially grandmothers. If all of us lived to be 120 years old, we would all have osteoporosis. It is important to do everything that we can to keep from having osteoporosis while we are alive.

A lot of research has been done on people in the general population who have never had cancer. From these studies, we know several things. First, there are certain factors that we cannot change that affect our chance of developing osteoporosis. Genes are important-if you have someone in your family with osteoporosis, you are more likely to also develop it. Women have this disease about four times as often as men. Hormone replacement, or taking estrogen pills, reduces this risk in females who have gone through menopause. Similarly, osteoporosis is more common in Caucasians and Asians than African Americans or Latinos, and more common in very thin or short people. So, if you are a slim, white female whose mother developed osteoporosis, you have a high risk of developing it yourself.

Research has also shown us that there are many things that we can do to prevent osteoporosis. Regular exercise and eating a diet that has enough calcium and vitamin D are very important to keep the bones strong. This is especially important in our teenage and young adult years as we are reaching the peak of our bone mass or strength. If we do not exercise or have enough calcium in our diet, we may not reach a normal peak and so when we start to lose calcium from our bones, we can develop osteoporosis at a younger age. Exercise and calcium are not only important for our teenage and young adult years, but throughout our life they can help keep our bones strong.

There are several things that cause the bone to lose calcium at a faster rate, which can lead to osteoporosis at a young age. Smoking is the worst culprit. There is also research to suggest that consuming too much caffeine, drinking carbonated beverages, and eating too much salt may cause an increase risk for bone fractures and osteoporosis.

Childhood cancer survivors and their bones

Many of the therapies used to treat childhood cancer can affect the strength of bones. That makes sense, since children's bones are growing and developing when they receive chemotherapy, radiation, and surgery. Because this is such an important issue, there are a growing number of studies looking at how cancer treatment affects the growth and development of bones.

Based upon early studies, we know that cancer treatment can affect the bones in two different ways, both of which may occur in some survivors. First, because of treatment, the survivor may never reach a normal peak bone mass or density. This is shown in the following graph that shows the bone mineral density or strength of the bone as we age. Note, in the average person, the strength of the bone gradually decreases with age. The survivor, on the other hand, does not reach the normal peak strength of the bone and so may develop osteoporosis at a younger age.

Also, a survivor may lose bone at a faster rate than normal, as shown in the next graph.

Some survivors may have both problems-a lower peak bone mass and a faster rate of loss of calcium from their bones, which may lead to osteoporosis at a much younger age. Needless to say, other factors can add to this problem. If a survivor is a thin white female who smokes and does not exercise, she is at a very high risk. It is important to remember that male survivors are also at risk.

So, which treatments can cause a problem and increase the risk for osteoporosis? The following information is based on early studies. We hope that much more will be learned in the next few years to help better understand individual risks. The following groups of survivors appear to be at risk for developing osteoporosis at a younger age:

  • Survivors at highest risk are those who have ovarian or testicular failure from radiation below the diaphragm (abdominal or pelvic/gonadal radiation), and/or took high doses of alkylating medications (cyclophosphamide, ifosfamide). Similarly, survivors who experience early or premature menopause may have a faster loss of calcium.
  • Survivors with premature or early puberty tend to have an early end of their growth spurts, thus may not reach a normal peak bone mass.
  • Survivors who took or take medications such as glucocorticoids (prednisone, dexamethasone) and/or methotrexate can have decreased bone mass. Steroids have a direct effect on bone, causing problems with bone formation, decreased calcium absorption from the intestine, and increased excretion of calcium through the kidneys.
  • Survivors who had whole brain or cranial radiation.
  • Survivors who were bed ridden for long periods.
  • Survivors who do not exercise during and after treatment. Weight bearing exercise (walking, jogging, most sports) causes bone mass to increase.
  • Survivors who have inadequate calcium intake.

What can a survivor do to lower the risk of osteoporosis?

Two very important things can be done by all survivors to lower their risk: be physically active and take adequate calcium.

Exercise and a physically active lifestyle

If a survivor picked the one thing that would have the greatest impact on his/her life and lower the risk for a number of late effects and common adult health problems, it would be to make a lifetime habit of being physically active. Regular exercise, four times a week for about thirty minutes, makes a huge difference in the strength of our bones.

Suggestions for exercise:

  • Simple walking is GREAT!
  • If you are not active, begin slowly and build up each week
  • You can exercise for short periods several times a day.
  • Alternate the types of exercise to keep it fun.
  • Use other ways to increase your activity level. Use the stairs rather than the elevator. When weather permits, park a few blocks from the store or office and walk. Mow your own lawn. Take an exercise break at work.

Some survivors are limited to certain types of activity because of surgeries or other treatments for their cancer. If you have a problem with deciding how to best exercise or be active, sit down and discuss the options with your physician or health care provider.

Calcium

Most people do not have an adequate amount of calcium in their diet. The National Osteoporosis Foundation recommends that all adults have a daily dietary intake of 1000 to 1200 mg of calcium each day. Some physicians recommend that survivors get 1500 mg a day. The main sources of calcium in the diet are dairy products (milk, yogurt, cheese) and green, leafy vegetables.

Calcium in foods:

  • Milk (8 ounces) 300 mg
  • Yogurt (8 ounces) 400 mg
  • Cheese (1 ounce) 200 mg
  • Broccoli (1/2 cup) 47 mg
  • Pinto beans (1/2 cup) 40 mg

An excellent web site with a calculator to help determine the amount of calcium in your diet is http://www.calciuminfo.com/index.htm

If your diet is low in calcium and you are unable to get the level up to 1200 to 1500 mg per day, then taking a calcium supplement pill is recommended. A wide variety of calcium supplements are available at the grocery or health food store. See the following web site for a discussion of calcium pills: http://www.nof.org/prevention/calcium_supplements.htm

Other important things that a survivor can do to lower the risk for osteoporosis:

  • Don't smoke
  • Don't drink more than one alcoholic drink per day (e.g. 12 oz. beer or 5 oz. of wine or 1.5 oz of 80-proof distilled spirits)
  • Avoid excessive intake of caffeinated products-they can increase the loss of calcium through the kidneys and drain off skeletal calcium
  • Avoid excessive consumption of carbonated soft drinks

What follow up is needed for those at risk?

First, it is important that all survivors be physically active and get enough daily calcium. Those who are at risk for osteoporosis should discuss screening options with their physician or health care provider. To date, we do not know the best way to screen survivors. Most of the research has been done in the general population, especially in women sixty-five years of age or older. For survivors at highest risk, such as those who have ovarian failure or premature menopause, it is reasonable to get testing to determine your current bone density. We do not know what screening is beneficial for other survivors, but a number of studies in process should provide some answers within the next few years.

Peak bone mass can be measured by a number of different methods, with dual energy x-ray absorptiometry (DXA or DEXA) being the most widely used technique. From this special x-ray of two or three sites (hip, wrist, low back), the bone density can be calculated. DXA has a low radiation dose and is fairly precision and accurate. The bone mineral density is reported as a "T-score", which is a comparison to the peak bone mass of young adults in the general population. Osteopenia (low bone mass) is a T-score between -1.0 and -2.5 standard deviations (SD; a unit of variation), while osteoporosis is defined as a T-score of < -2.5 SD. A single test, such as a DEXA, tells us how the bone mass is only at that time and does not tell you how rapidly calcium is being lost from the bone. A follow-up DEXA, generally one or two years later, can show how the bone mass is changing over time.

Based upon this information, your physician can discuss your bone strength with you and what further testing or treatment might be needed.

Some excellent web sites for more information are:

http://familydoctor.org This is a web site run by the American Academy of Family Physicians and includes general health information.

http://www.familydoctor.org/healthy.html discusses healthy habits, including exercise and calcium.

http://www.familydoctor.org/healthfacts/136/index.html discusses women and osteoporosis.

http://www.nof.org/prevention/index.htm The National Osteoporosis Foundation describes ways to prevent osteoporosis.

 
 

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