Canadian teens are developing ‘lazy bones.’ Here’s why

They swipe on their smartphones and tap away on their laptops, but how often are Canadian teens active? New research suggests that today’s growing adolescents are developing “lazy bones” that are weaker and more likely to break.

A new University of British Columbia study is warning that there’s a four-year window – between the ages of 10 to 14 for girls and 12 to 16 for boys – that’s crucial for bone health. It’s during this timeframe that as much as 36 per cent of the human skeleton is formed.

Physical activity offers bones their best chance of developing and strengthening. The problem is it’s during these pivotal years that adolescents tend to lead sedentary lifestyles, though.

“The skeleton and bone are really, really clever tissues so if you’re on screens or you’re doing anything where [bones] don’t have to be strong, they start to resorb very quickly so that when you do impose a load, they’re more likely to break or be injured,” Dr. Heather McKay, a UBC medicine professor, told Global News.

Tweet This Click to share quote on Twitter: "The skeleton and bone are really, really clever tissues so if you're on screens or you're doing anything where [bones] don't have to be strong, they start to resorb very quickly so that when you do impose a load, they're more likely to break or be injured," Dr. Heather McKay, a UBC medicine professor, told Global News.

During these years, adolescents encounter a growth spurt. In the subsequent six to eight months, their bones are “laid down” and “fill in,” she explained.

“The things you do around adolescence to build your bone strength can never be repeated,” she warned.

Tweet This Click to share quote on Twitter: "The things you do around adolescence to build your bone strength can never be repeated," she warned.

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McKay worked with PhD candidate Leigh Gabel for their study that looked at the exercise habits and bone health of 309 teenagers over a four-year period. The duo looked at high-res, 3D X-ray images to compare differences between youth who met daily physical activity recommendations compared to those who got less than 30 minutes of exercise per day.

“We found that teens who are less active had weaker bones, and bone strength is critical for preventing fractures,” Gabel said.

McKay said that there haven’t been long-term studies looking at physical activity in adolescence and comparing it to bone health in adulthood or as seniors. But retrospective studies have suggested that the elderly with frail, brittle bones were less active in their youth.

“It’s historical. We are meant to be moving and loading. All of our systems respond to physical activity and our bones are no different,” McKay said.

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Canadians struggle to meet daily guidelines for physical activity, which call for about 150 minutes a week for adults. Only 43 per cent of boys in the study were getting enough exercise, and only 11 per cent of girls hit targets. Keep in mind, women are at an increased risk of developing osteoporosis later in life.

Boys dealt with a high risk of breaking bones, though. A combination of factors makes up bone strength, from size, density and microarchitecture.

McKay said for adolescents, three to 10 minutes of certain activities go a long way. They should be taking on weight-bearing activities, such as running and jumping, to sports like soccer, Frisbee and basketball.

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“Bones like these short, sharp responses or stimuli – jumping, things like basketball, gymnastics, skateboarding. Short, sharp stimuli prompt bones to increase their strength … it’s a little bit of loading, but a little bit goes a long way,” McKay said.

It’s not too late for adults, either. While this years-long window to build skeleton closes, it doesn’t stop in its tracks. Adults are still forming skeleton but lose bone strength and density as they age. The process can be slowed through being physically active and making sure we’re getting enough calcium and vitamin D.

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Adults should also be taking on weight-bearing activities, such as running and jumping, to sports like soccer, ultimate Frisbee and basketball.

Gabel and McKay’s full findings were published in the Journal of Bone and Mineral Research.

carmen.chai@globalnews.ca
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