Digging into the research behind a seemingly improbable health claim.
One of those too-good-to-be-true health headlines has been making the rounds recently. “Dashing for the bus could protect against osteoporosis,” as the Daily Mail put it. “Just ONE MINUTE of running a day boosts bone health.”
Exaggeration? Well, the official press release says pretty much the same thing: “One minute of running per day associated with better bone health in women.” As for the journal paper, its title is a little more inscrutable – but the overall message is surprisingly similar. This is a neat result, and it’s worth digging into what the scientists found and why.
The study, from researchers at the University of Exeter and the University of Leicester, is published in the International Journal of Epidemiology, and takes advantage of a massive collection of data called the UK Biobank, which includes (among other things) activity-monitoring and bone health data from 100,000 people between the ages of 40 and 69. The researchers wanted to figure out if the patterns of physical activity measured by accelerometers could predict who had the healthiest bones.
There are, of course, lots of previous studies that have looked at questions like this. Surprisingly, some studies have failed to find any link between the amount of vigorous exercise people do and how strong their bones are. One possible explanation is that most accelerometer data is averaged over relatively long periods of time, typically 15 to 60 seconds, which “smoothes out” the most vigorous jolts of activity. That makes sense for studies of cardiovascular fitness, where sustaining an elevated heart rate is what matters. But for bone health, short high-impact jolts are thought to stimulate bone remodelling, so in this case the researchers measured peak acceleration data every second.
What sort of accelerations are we talking about? Testing indicated that, with this set-up, running at 7:30 per kilometre pace gives you a jolt equivalent to about 75 per cent of the force of gravity, while running at 6:00 min/km pace is about 100 per cent the force of gravity. Subjects in the study wore a three-dimensional accelerometer for a week, allowing the researchers to calculate how much time (summing up individual seconds) they spent above those two thresholds.
This is where the headline result comes from. For pre-menopausal women, accumulating at least one minute per day above the 100-per-cent-gravity threshold offered a statistically significant improvement in bone mineral density and other measures of bone health. Accumulating at least two minutes gave an even bigger boost.
For post-menopausal women, the same pattern was seen at the lower 75-per-cent-gravity threshold. In broad terms, that suggests older women only need to jog to get the same bone benefits that younger women get from quicker running. That may be because your biomechanics change as you get older, resulting in a more jarring impact with each stride. Or it may be because your bones get weaker as you age, so require less of a stimulus to get stronger. There’s a bit of evidence for both those possibilities, but not definitive in either case.
Are these findings a massive surprise? Not really. There are three basic ways you can stimulate your bones to get stronger. One is simply to be on your feet a lot, doing weight-bearing exercise. This is no longer thought to be a particularly effective way of strengthening your bones, but there is some evidence that people who walk a lot tend to have stronger bones.
Another approach is to do resistance training. Strengthening your muscles puts tension on your bones, which in turn triggers them to get stronger.
The third approach, which seems to be the most powerful trigger of all, is jarring impacts. Simply jumping as a high as you can a few times a day can have powerful effects on your bones. In fact, after somewhere between 40 and 100 impacts, the bone benefits seem to max out, so this is a case where more isn’t necessarily better. Studies have found positive effects from simple intervention like 10 jumps, three times a day in schoolchildren, or five sets of 10 jumps three times a week in adult men.
Thanks to the detailed every-second analysis of the accelerometer data, this new study confirms that you don’t necessarily need to do jump-specific exercise – running itself gives you the jarring impacts you need. That helps explain why, for example, runners tend to have better bone density than cyclists.
This doesn’t mean you should only run for one minute per day. There are, of course, many other benefits to running. But it does suggest yet another reason to include some short bursts of fast running in your routine a few times a week, because the impacts are highest when you’re running fast. And in this case, the too-good-to-be-true headlines turn out to be more or less true: even a minute or two is enough to make a difference.