Welcome to Impact Factor, your weekly dose of commentary on a new medical study.
I'm Dr. F. Perry Wilson of the Yale School of Medicine.
10,000 steps a day.
I know you’ve heard the number.
A number that reminds us to get up, move around, walk to the store instead of drive there.
10,000 steps is achievable, but not precisely easy, at least if you have a job that keeps
you sitting in front of a computer for 8 hours a day.
And, with smartphones in our pockets, knowing if you’ve hit that magic mark is trivial.
As far as health interventions go, encouraging people to walk 10,000 steps a day is pretty
low risk, and the price is certainly right.
But the benefit is harder to tease out.
That is why I got intrigued by a new study in JAMA Internal Medicine that looked at the
link between steps taken and the risk of death and found something novel.
It’s not just how many steps you take.
It’s how you take them.
The study leveraged the UK Biobank cohort – a longitudinal study of British adults
that collects a lot of data over time, but does not collect step counts.
So the authors e-mailed over 200,000 cohort participants asking them if they’d wear
a step counter – actually a pretty fancy step counter called an Axivity AX3 accelerometer
– 24-hours a day for seven straight days.
Nearly 50% responded that they would – a really impressive response rate I can say
as someone who would give my own pinky for a 50% consent rate for one of my studies.
Of course, not everyone wore the thing when they got it or had adequate data, but in the
end the authors had a pretty huge dataset – 78,500 people with 7 days of step data.
And it wasn’t just step counts.
The authors wondered if all steps are the same.
After all, there are the steps we take just sort of living our lives – walking to the
water cooler – that sort of thing.
The study called these incidental steps.
There were the purposeful steps – the steps we take when we are actually going somewhere.
They also measured something they call the Peak-30 cadence – think of it as the peak
walking speed during the day.
Are all steps created equal?
They linked these various metrics to all-cause mortality, as well as cardiovascular and cancer-specific
mortality.
Let’s start off simply with step count.
As you can see here, as step counts increased, the risk of death went down, but there are
a couple of interesting things to note here.
First, there was no lower limit to benefit, 3000 steps was better than 2000 which was
better than 1000.
Second, the benefit seemed to level off after 10,000 steps or so.
Maybe it is a magic number.
Of course, the data gets sparser out in the high-step counts, so we don’t want to jump
to conclusions.
Overall, the authors report a relative reduction in death rate of 36% for people hitting that
10,000 mark.
All studies like this are plagued by what we often call reverse causation.
Maybe steps don’t promote health, maybe healthier people take more steps.
The authors account for this by excluding deaths that happen within two years of the
step assessment – so we can be somewhat reassured that these weren’t people who
were very ill when the step counts were done.
They also adjusted for a slew of factors including age, sex, race, education, smoking, alcohol
use, social deprivation, fruit and vegetable consumption and so on.
Perfect?
No.
But not bad.
But what’s really interesting is the findings for those other types of steps.
Putting the data altogether, there is a good signal that any steps are good, but purposeful
steps – really walking somewhere – are a bit better.
About 5000 purposeful steps had the same effect as 10,000 total steps.
And of course, how you walk matters.
A higher step cadence was associated with reduced overall mortality too – with the
best rate being about 75 steps a minute which is definitely a brisk walk.
But it might be worth it – the top 20% in the cadence analysis – the speed walkers
if you will – had a 34% lower death rate than the lowest 20%.
The results were broadly consistent when the cause of death was examined, though a bit
stronger for prevention of cardiovascular deaths and a bit weaker for prevention of
cancer deaths.
In the end, this data supports what really is becoming a huge body of literature suggesting
that sedentary lifestyles increase mortality risk.
It also tells us that though 10,000 steps is really good, any steps are good, so if
you usually get 2000, shoot for 4000.
If get 4000, shoot for 8000.
And walk somewhere.
Not every step is the same – and a purposeful walk – perhaps a brisk walk – will get
you there a bit healthier.
For Medscape, I'm Perry Wilson.