Study: Teenage couch potatoes will have brittle bones for life

Canadian teens spend too much time sitting and not enough time moving. Only 5% of 12 to 17-year-olds get the 60 minutes of heart-pumping physical activity they need each day.

We know inactivity is partly to blame for increasing waistlines and skyrocketing rates of type 2 diabetes among Canadian youth, but it’s also bad for their bones.

A recent study published in the Journal of Bone and Mineral Health by researchers at the University of British Columbia, looked at the relationship between physical activity, sedentary time, and bone strength in adolescents. Over four years, they took high-resolution scans of 173 girls’ and 136 boys’ forearms and shins to measure their bone strength. The same teens’ activity levels were measured using accelerometers.

The results are scary.

WHAT WAS FOUND?

Unfortunately, the teens who were less active had significantly weaker bones than those who were more active.

Overall, the study participants were actually more active than average teens. About a quarter, or 24%, of participants got the daily 60 minutes they need according to the physical activity guidelines, although the levels decreased as they aged. As for sedentary time, on average participants spent a whopping 9.1 hours per day being sedentary.

What’s even more startling, though, is the fact that getting enough physical activity didn’t counteract the ill effects of the whopping sedentary time. Kids who spent too much time sitting, even if they were active otherwise, still had weaker shins.

These findings are concerning because they show that a lack of load- or weight-bearing activity throws off the bone formation-resorption balance. In other words, inactivity is causing teens’ bones to not absorb minerals properly and inhibiting the formation of new cells. If teens don’t use them, they will lose them.

Young Canadians are spending too much time being sedentary, increasing their risk for broken bones now and of developing osteoporosis later in life. Extensive sitting is causing major, irreversible damage to their skeleton.

FOUR CONCLUSIONS

1. Teens need to move more and sit less. Canadian teens are growing thinner, weaker bones because of their current lack of activity. This needs to change.

2. Teens should participate in bone-strengthening activities three times a week. Examples of good weight-bearing activities include running, skipping, tennis, gymnastics, basketball, and resistance training.

3. Outdoor activities are important too. Our bodies need the right vitamins and minerals to build strong bones. Getting outside more often can be a great way to ensure teens are getting enough vitamin D, which plays a critical role in forming strong bones. Plus, getting outside almost always leads to less sitting and more moving.

4. We must start early. At ParticipACTION we’re fond of saying it’s never too early or late to start. As a general rule, this is great advice because physical activity can have many immediate benefits, even if you’ve been inactive for a long time.

But in this case, there is such a thing as too little too late. Our bones are formed and grow dense before the age of 30, and being active during this time is critical. Getting active later can still have some bone benefits, but it can’t undo the hours of sitting as a younger person.

In life, we only get one chance to build strong bones, and to do that, teens need to start immediately moving more and sitting less.

Heart disease and diabetes used to only affect the old. If the current levels of inactivity persist, we may start to see cases of osteoporosis in younger people as well.