Regular walking breaks 'protect arteries'

“Just a five-minute walk every hour helps protect against damage of sitting all day,” the Mail Online reports.

A study of 12 healthy but inactive young men found that if they sat still without moving their legs for three hours, the walls of their main leg artery showed signs of decreased flexibility. However, this was “prevented” if the men took five-minute light walking breaks about every hour.

Less flexibility in the walls of the arteries has been linked to atherosclerosis (hardening and narrowing of the arteries), which increases the risk of heart disease.

However, it is not possible to say from this small and short-term study whether taking walking breaks would definitely reduce a person’s risk of heart disease.

There is a growing body of evidence that spending more time in sedentary behaviour such as sitting can have adverse health effects – for example, a 2014 study found a link between sedentary behaviour and increased risk of chronic diseases.

While this study may not be definitive proof of the benefits of short breaks during periods of inactivity, having such breaks isn’t harmful, and could turn out to be beneficial.

Where did the story come from?

The study was carried out by researchers from the Indiana University Schools of Public Health and Medicine. It was funded by the American College of Sports Medicine Foundation, the Indiana University Graduate School and School of Public Health.

The study has been accepted for publication in the peer-reviewed journal Medicine & Science in Sports & Exercise.

The coverage in the Mail Online and the Daily Express is accurate though uncritical, not highlighting any of the research's limitations.

What kind of research was this?

This was a small crossover randomised controlled trial (RCT) assessing the effect of breaks in sitting time on one measure of cardiovascular disease risk: flexibility of the walls of arteries.

The researchers report that sitting for long periods of time has been associated with increased risk of chronic diseases and death, and this may be independent of how physically active a person is when they are not sitting. This is arguably more an issue now than it would have been in the past, as a lot of us have jobs where sitting (sedentary behaviour) is the norm.

Short breaks from sitting are reported to be associated with improvements in a lower waist circumference, and fats and sugar in the blood.

A randomised controlled trial is the best way to assess the impact of an intervention on outcomes.

What did the research involve?

The researchers recruited 12 inactive, but otherwise healthy, non-smoking men of normal weight. These men were asked to sit for two three-hour sessions. During one session (called SIT), they sat on a firmly cushioned chair without moving their lower legs. In the other (called ACT), they sat on a similar chair but got up and walked on a treadmill next to them at a speed of two miles an hour for five minutes, three times during the session. The sessions were carried out between two and seven days apart, and the order in which each man took part in these sessions was allocated at random.

The researchers measured how rapidly the walls of the superficial femoral artery recovered from being compressed by a blood pressure cuff for five minutes. The femoral artery is the main artery supplying blood to the leg. The “superficial” part refers to the part that continues down the thigh after a deeper branch has divided off near the top of the leg.

The researchers took these blood pressure measurements at the start of each session, and then at hourly intervals. The person taking measurements did not know which type of session (SIT or ACT) the person was taking part in. The researchers compared the results obtained during the SIT and ACT sessions, to see if there were any differences.

What were the basic results?

The researchers found that the widening of the artery in response to blood flow (called flow-mediated dilation) reduced over three hours spent sitting without moving. However, getting up for five-minute walks in this period stopped this from happening. The researchers did not find any difference between the trials in another measure of what is going on in the arteries, called the “shear rate” (a measurement of how well a fluid flows through a channel such as a blood vessel).

How did the researchers interpret the results?

The researchers concluded that light hourly activity breaks taken during three hours of sitting prevented a significant reduction in the speed of the main leg artery recovering after compression. They say that this is “the first experimental evidence of the effects of prolonged sitting on human vasculature, and are important from a public health perspective”.

Conclusion

This small and very short-term crossover randomised controlled trial has suggested that sitting still for long periods of time causes the walls of the main artery in the leg to become less flexible, and that having five-minute walking breaks about every hour can prevent this.

The big question is: does this have any effect on our health?

The flexibility of arteries (or in this case, one particular artery) is used as what is called a “proxy” or “surrogate” marker for a person’s risk of cardiovascular disease. However, just because these surrogate markers improve, this does not guarantee that a person will have a lower risk of cardiovascular disease. Longer-term trials are needed to determine this.

The potential adverse effects of spending a lot of time sitting, independent of a person’s physical activity, is currently a popular area of study. Standing desks are becoming increasingly popular in the US, so people spend most of their working day on their feet. Some even bring a treadmill into their office (see this recent BBC News report on desk treadmills).

Researchers are particularly interested in whether taking breaks from unavoidable periods of sitting could potentially reduce any adverse effects, but this research is still at an early stage. In the interim, it is safe to say that having short breaks from periods of inactivity isn’t harmful, and could turn out to be beneficial.

There has been a rapid advancement in human civilisation over the past 10,000 years. We have bodies that were evolved to spend a large part of the day on our feet, hunting and gathering, but we also now have lifestyles that encourage us to sit around all day. It could be that this mismatch partially to blame for the rise in non-infectious chronic diseases, such as type 2 diabetes and heart disease.

If you feel brave enough, why not take on the NHS Choices 10,000 steps a day challenge, which should help build stamina, burn excess calories and give you a healthier heart.