Running, jumping, walking and weightlifting have something in common—they build bone density and strength. Hematologists now recommend some degree of bone-building physical activity for children with bleeding disorders. Nevertheless, osteoporosis, a disease usually linked to old age and old bones that become thin and brittle, is showing up in kids with hemophilia.
“In children, osteoporosis is still a rare problem, but we’re finding it more often that we would like to,” says Mindy Simpson, MD, pediatric hematologist/oncologist at Rush University Medical Center in Chicago. Her institution is analyzing data from a study of pediatric and adult patients. “It’s a matter of trying to define what we think the prevalence is, what we think the incidence may be and who is at highest risk.”
Defining at-risk patients will help pediatric hematologists devise standard protocols for screenings and preventive measures. Until then, parents can increase their awareness of pre-existing conditions or behaviors that may predispose children for osteoporosis. Understanding the body’s need for calcium and vitamin D as children grow can help parents create a proactive plan for their kids so they can build better bones.
Bone Building
The skeleton provides a strong framework to keep organs in place, and for attachment of ligaments, muscles and tendons. Its bones are like miniature construction sites, where building and demolition teams work round the clock. The osteoblasts are the cells that build bone; the osteoclasts remove it. Ideally, the builders should outnumber the destroyers from childhood until young adulthood. Their goal is to amass as much bone as possible, called peak bone mass, by the time a person is 25–30 years old.
Hormones, gender, genetics, diet and exercise all affect bone mass. Boys’ bones tend to have more mass and density than girls’ bones. During the teenage years, hormones kick in, causing growth spurts and sudden increases in bone density. “This is a very pivotal time for kids to be accruing bone mass, which is essential for the rest of their life,” says Simpson.
Bone mass and density are increased through weight-bearing exercises, such as weight lifting, that force muscles to pull on your bones. “Bone is partially a crystalline structure and it generates a small electrical current that stimulates the cells to make more bone,” says James V. Luck Jr., MD, director of orthopedics and rehabilitation at the Hemophilia Treatment Center at Los Angeles Orthopaedic Hospital.
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Bones also need vitamins and minerals to stay strong. Vitamin D, the so-called “sunshine vitamin” because your skin makes it from ultraviolet rays in sunlight, is a partner in bone building because it helps the body absorb calcium. (See “Bone Up,” HemAware, Spring 2011, p. 10.) Calcium is needed to build bones and teeth and maintain their strength.
Vitamin D and calcium can be obtained in a variety of foods and also through vitamins and supplements. Dairy products are loaded with calcium, as are some types of fish and other foods, including produce. (See sidebar, “Calcium Choices.”) “There is a decent amount of calcium in green leafy vegetables, like broccoli,” says registered dietitian Tina Willis, MA, RD, CD, Indiana Hemophilia & Thrombosis Center in Indianapolis.
The Link Between Hemophilia and Osteoporosis
Certain circumstances associated with hemophilia can increase a child’s risk of developing osteoporosis. Top among them are the periods of inactivity when a child is recovering from a bleed or surgery. “It’s not only the fact that they’re not weight-bearing, but it’s the fact that they’re immobilized,” says Susan Bukata, MD, an orthopedic surgeon in Santa Monica, California. Even a few weeks of immobility can lead to decreased bone mass. “When they go back to weight bearing, they’ll gain some of it back, but they’ll never gain it all back.” When bone development is interrupted, it increases the risk of osteoporosis. “Osteoporosis is a lifelong disease that, for a lot of people, begins during childhood,” Bukata says.
Another contributor is the fear factor. “The osteopenia, or thinning of the bones (a precursor to osteoporosis) may be due to kids with hemophilia having reduced activities, either because parents are overly protective, or the kids themselves are protective as they get to the teen years,” says Guy Young, MD, director of the Hemostasis and Thrombosis Center at Children’s Hospital Los Angeles. “That is when a lot of bone gets put on.”
A 2004 study of 19 children with severe hemophilia in Melbourne, Australia, showed that those with the most damage from bleeds into their ankles and knees also had significant loss of bone density in the lumbar (lower) region of their vertebrae. The most likely explanation for the decreased bone density was lack of physical activity, specifically weight-bearing exercise. Screening for osteoporosis was recommended for at-risk children with hemophilia who had joint damage from bleeds.
Patients with inhibitors, antibodies to infused factor product, are at higher risk for osteoporosis. Because their bleeding is often not well controlled, they can develop target joints. The synovium, the membrane lining the joint, becomes irritated by the influx of iron and other components of the blood. This can lead to synovitis, a chronic condition in which the synovium becomes inflamed and thickened, prone to even more bleeding. Synovitis, in turn, can impair bone growth.
“Chronic inflammation, especially from synovitis, can cause the release of tissue necrosis factor, or TNF-alpha,” says Bukata. TNF-alpha is a cytokine, a protein produced by the immune system that activates osteoclasts, increasing the rate of bone destruction. “The see-saw is then tipped in the direction of bone loss,” she says. “When your body is not in balance for calcium, it steals it from your skeleton.”
The pediatric patients diagnosed with osteoporosis in the Rush study had a history of synovitis—one in his ankles, the other in his knees. Both had severe hemophilia and inhibitors. Compared to their peers on prophylaxis, these two bled a lot. In a one-year period, the older teen had dozens of bleeds; the younger one had more than 10. But it’s not clear if repeated joint bleeds, followed by periods of rest and/or lack of exercise, caused their osteoporosis, Simpson says.
Then there’s the issue of weight gain. Being overweight taxes joints and limits range of motion in children with hemophilia. A 2004 study by the Centers for Disease Control and Prevention showed that nearly one-third of the boys and teens treated at the hemophilia treatment centers (HTCs) they surveyed were overweight or obese. “Obesity definitely leads to inactivity, which then can make osteopenia worse,” Young says.
Osteoporosis Diagnosis
Symptoms of osteoporosis can be subtle or nonexistent. Had the two boys not been in the Rush HTC study, Simpson doubts their osteoporosis would have been identified. “Osteoporosis is a silent disease,” says Bukata.
That’s why tests confirming osteoporosis are performed, the gold standard of which is the dual-energy X-ray absorptiometry, or DEXA, scan. It uses radiation to measure bone density at sites of frequent fractures—the wrist, the spine and the head of the femur (the long thigh bone). If the results are at least two standard deviations below those of healthy peers and the child has a clinically significant history of bone fractures, osteoporosis is presumed, according to the International Society of Clinical Densitometry. However, because children’s bones are less dense than adults’, the DEXA scan is not always accurate.
Other tests may be needed to confirm bone loss. Lab tests can provide clues on the levels of calcium, potassium (which helps the body absorb calcium), and vitamin D in the blood. X-rays can furnish proof that bones are brittle, but only after a loss of 40% or more of their mineral content, says Luck. He looks for changes in the trabeculae, the spongy tissue in the center, and in the cortical, or compact, bone on the outside. “The lines in the trabelular bone pattern start to disappear and they become coarser. There are fewer of them,” Luck says. “Also, the cortices, which are normally nice and thick and strong, start to get thin.”
Healthy Bone Basics
Having healthy bones means getting back to basics—good nutrition, plenty of exercise and daily exposure to some sunshine. A 2010 study by the National Institutes of Health (NIH) showed that only 12% of girls and 17% of boys were getting the recommended daily allowance of calcium. Further, 9% of children and 61% of teens were severely deficient in vitamin D, a trend also found in patients with hemophilia. “More than half the subjects in our study had low vitamin D levels,” Simpson says.
In kids, it’s more beneficial to boost their calcium intake through diet, than supplements or vitamins, say experts. “You’re actually getting a balance of calcium phosphate, magnesium and vitamin C through different foods,” says Bukata. An 8-ounce glass of milk at breakfast, a piece of string cheese at lunch and a 6-ounce cup of yogurt at dinner supply the 700 mg of calcium needed by most kids, she says.
But vitamin D is different. Now that people are slathering on the sunscreen, it’s hard to tell if you’re truly absorbing your 15-30 minutes daily dose of vitamin D in the great outdoors. Although there are vitamin D-rich foods, such swordfish, salmon and tuna, and foods fortified with it, including orange juice and cereal, it’s difficult to reach the recommended daily amount through diet alone. Although the Institute of Medicine recommends 600 units of vitamin D per day for children, individual needs can vary. “Some kids are going to need more than you would expect,” says Bukata. “For kids with hemophilia, it might be a good idea to have a baseline vitamin D through a blood test, just to know where they are.”
Approved Activities
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Prophylaxis has opened the door to a wide array of approved activities. “We have definitely shifted our thinking about how much pounding joints can take,” Simpson says. A 2009 study in Pediatrics concluded that in boys with severe hemophilia who were on prophylaxis, high-impact sports, such as running and skateboarding, did not produce more bleeds than low-impact sports, like golf and swimming. (See “Jump Start,” HemAware, Spring 2010, p. 10.)
That may mean letting your kids do some bone-building activities, within reason, after school. “We try to keep them as active as we can within the constraint of what’s going on with their particular joints,” says Sharon Funk, PT, DPT, at the University of Colorado Denver Hemophilia and Thrombosis Center in Aurora. “If there is a complicating factor, like an inhibitor, you have to approach any form of exercise very cautiously.”
Walking is a good weight-bearing exercise for kids, Funk says. Running is usually fine when kids are young and play rudimentary games of soccer and basketball. When the games get more competitive and contact occurs, such as during junior high and high school, there is a higher likelihood of injury or bleeds, says Funk.
Lifting weights, on the other hand, is a bone-healthy activity. The muscles attached to the bones pull on them, creating resistance. “That provides a form of stress on the bone, which stimulates it to form more bone,” Funk says. She prefers ellipticals and NordicTracks over treadmills, because of their gliding motion. They’re probably more suited to teens and young adults than younger children, she says.
The schoolyard favorite, the jump rope, receives praise from PTs. “There’s probably nothing better for building bone density than jumping and landing,” says Funk. But kids with ankle or knee issues should avoid that steady pounding, Funk says. Instead, they could reap similar rewards by dribbling a basketball toward the hoop and doing lay-ups.
Opportune Time for Osteoporosis Study
Although osteoporosis is unexpected in kids, researchers and HTC staff see this as an opportune time for study and analysis. The growing awareness of its existence is a good start, says Simpson. The next step is to determine who is most at risk. “Maybe it’s not just the inhibitor patients, but the ones who have more problems earlier in life,” she says. “Hopefully between several places that are putting data together, we’ll be able to define who they are.”