Space-age lessons could protect childhood cancer survivors’ bone health

Space has inspired and delighted people for centuries. The much-anticipated advent of crewed spaceflight taught invaluable lessons, even for the most unexpected groups back on terra firma. In the 1960s, astronauts returned from microgravity with decreased bone density. This decrease revealed that bones must undergo constant stress to grow and maintain themselves.

Survivors of childhood cancer, while seemingly unrelated to astronauts in the weightlessness of space, are one group unexpectedly impacted by this revelation. These two distinct groups share a connection in the loss of bone density occurring during a significant life event. Children receiving cancer treatment are often sedentary due to their therapy. Their listlessness mimics microgravity’s effect on astronauts, while the treatment itself may also negatively impact their bone health.

Recent research spearheaded by first author Chelsea Goodenough, PhD, St. Jude Department of Epidemiology and Cancer Control, characterized bone mineral density loss in survivors of childhood cancer. Published in JAMA Network Open, her study looked at survivors five or more years after treatment using the St. Jude Lifetime Cohort Study (St. Jude LIFE). She found that survivors were more likely than age-matched peers to experience low bone mineral density. Low bone mineral density predicted a higher chance of lacking independence, including being unemployed or requiring a personal care attendant, highlighting the need to find ways to intervene to protect and promote survivors’ bone health.

“Glucocorticoids given during cancer therapy can act as a giant hammer to bone mineral density,” said corresponding author Kiri Ness, PT, PhD, FAPTA, St. Jude Department of Epidemiology and Cancer Control. “We found that this loss could have long-term consequences for survivors. We saw 30-year-olds that functionally looked like they were in their 70s and 80s, showing the need for early interventions after treatment.”  

Modifiable factors influence survivors’ bone mineral density

“The unique aspect of this study is that we calculated the extent to which different factors contributed to loss of bone density,” Ness said. “That gives us a starting place to design interventions.”

Bone loss decades after treatment could be related to therapy, something investigators can’t change after the fact, but potentially modifiable factors could also be contributing. The St. Jude researchers wanted to see if they could identify any modifiable factors that could point to protective interventions for further investigation.

“We found that about 33% of bone density loss was due to cranial radiation for those who received it,” Ness explained. “But about 25% of the deficit was related to hormone deficiencies, such as hypogonadism.” Hypogonadism is a common consequence of childhood cancer therapy. During treatment, the patient receives hormone-disrupting chemicals, sometimes resulting in an extended deficiency of sex hormone production (testosterone or estrogen) and human growth hormone. These three hormones are known to have significant impacts on bone health. Since hormone replacement therapies already exist, the study has identified an area for potential pharmaceutical intervention to address hypogonadism to improve bone density among survivors of childhood cancer. 

Lifestyle changes can impact bone health

“Compared to hypogonadism, smoking and sedentary behavior were responsible for a smaller but still significant decrease in bone density,” Ness said. “But we already have interventions for both; we just need to test them for their effect on bone mineral density.”

Sedentary behavior is a common experience during treatment. “Understandably, kids don’t feel good during cancer therapy,” Ness explained. “So, they lay in bed.” Lying in bed acts like microgravity: The kids don’t put stress on their bones, resulting in bone loss. However, survivors can prevent this with physical activity. Exercise has already been shown to help protect cardiovascular health among survivors, so the research provides another potential motivation for exercise.

Ness, whose research focuses on lifestyle interventions to support survivors of childhood cancer, already promotes the positives of physical activity. Her insistence, bolstered by this study, has gained her a reputation among patients. “The kids on the floor call me the ‘exercise lady,’” Ness proudly acknowledged. “When they see me, they say, ‘Here she comes, the exercise lady is here.’”

Physical activity to improve bone health could be as simple as jumping or as elaborate as a dedicated heavy weight-lifting program. The increased activity will likely promote bone maintenance and, hopefully, growth, a parallel to the exercise program astronauts undergo upon returning from space to reestablish their bone mass.

While exercise is one way in which survivors can improve their bone health, the study also suggested that those who develop a smoking habit may have one more reason to quit. Survivors who smoked were more likely to have a moderate or severe bone mineral density deficit, along with a host of other problems.

“Smoking is just a bad idea for survivors,” Ness said. “Smoking causes a lot of ill effects, not just bone loss. So, we need to encourage young cancer survivors never to start and give cessation interventions to those that have.” Over 20% of survivors in the study currently smoked, indicating a significant opportunity for intervention.

Better understanding means more chances to help

By attributing the sources of bone mineral density loss, the St. Jude scientists have created a roadmap for exploring potential interventions. The ultimate goal is to give survivors of childhood cancer as much independence as possible to take control of their futures.

“I want survivors to know that if they have low bone mineral density, it’s not an insurmountable problem,” Ness said. “You can be proactive — by being physically active, avoiding smoking and making sure your physician understands your chronic health condition. That’s how you give yourself the best chance of having an independent life as an adult, chasing your dreams.” 

Maybe, one day, they could even become an astronaut.