Volume 9, Number 12 March 1, 2002

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Graduate Student Profile

Grad student makes key finding in children’s bone density

By Elizabeth Frogley

Successful Kinesiology PhD candidate Shawn Davison

When Shawn Davison started studying bone development, he wondered why adolescents are so likely to break bones at a time when their bone density should be increasing.

Davison, who recently completed a PhD in Kinesiology at the University of Saskatchewan, researched how and when people gain bone mass. Researchers believed bone mineral density constantly increases through adolescence, but kids are most likely to break bones when they are growing the fastest.

"My question here was: "Why are children fracturing bones at a point when they are increasing in density?" he says.

His answer: contrary to all previous research, bone mineral density decreases during adolescent growth spurts.

"I found that in fact children’s bone mineral density decreased during the period of maximum growth," Davison says. "After the growth spurt there was generally a rebound in density, which then increased until adulthood. This was dramatically different from the constant increase in bone mineral density over adolescence previously reported in hundreds of research articles."

Previous findings were flawed because of the equipment used to measure bone mineral density, Davison discovered.

"One of the biggest problems with the measurement of bone mineral density is that the best tool we have, a dual-energy x-ray absorptiometer (DXA), is incorrectly influenced by the physical size of the bone — larger bones will have their density overestimated and smaller bones underestimated."

Davison worked out a mathematical formula to adjust the DXA results and find an accurate bone mineral density that wasn’t influenced by the bone size. He then compared his results to fracture rates in Saskatchewan adolescents.

"It was one of those moments that scientists dream of — there was a perfect inverse relationship between bone mineral density and fracture rates," he says.

Bone mineral density is important because most bone mass is built up in the four years around a person’s peak growth. "This exceedingly rapid rate of accrual makes positive behavior, such as optimal calcium intake and physical activity, so beneficial at this time; but negative behaviors, such as smoking and hormonally insufficiency, so destructive," Davison says.

If bone mineral density isn’t built up during adolescence, osteoporosis is more likely to develop as bone mineral naturally decreases over time. For this reason, Davison says, "osteoporosis can be considered a paediatric disease."

Osteoporosis is characterized by low bone mass and deterioration of bone tissue. The disease can reduce mobility and cause fractures, particularly of the hip, spine, and wrist. It’s very common, affecting 1.4 million Canadians.

Davison hopes his research will lead doctors to rethink the way they diagnose low bone density. "Paediatricians may be treating a lot of children who do not need it, particularly if they are just small kids and perfectly healthy — in that instance the DXA would wrongly assume a lower density than the child actually possessed."

His findings will also influence future research. "I would hope that some of the equations that were developed could be used in clinical practice, to better assess when a child does have too little bone and should be managed."

Davison is now a clinical research scientist with the Osteoporosis Society of Canada. He is heading the largest review of osteoporosis literature ever attempted, with assistance from osteoporosis researchers from all over Canada.

He’ll write the guidelines for the prevention and treatment of osteoporosis in Canada 2002 based on the results of this review.

Davison plans to continue his research at either McMaster Medical School or Johns Hopkins Medical School, and says his time at the U of S has left him well-prepared for a career in research.

"I chose the U of S over all other schools because of the reputation of the paediatric bone physiologists here — they are second to none."

Elizabeth Frogley writes graduate student profiles as part of her Graduate Student Fellowship work for the College of Graduate Studies & Research.

For more information, contact communications.office@usask.ca

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