Moderate physical activity linked to longer lifespan...

"Just one brisk walk a week cuts risk of early death by 70% in older women, study claims," is the headline in the Mail Online.

The news comes from a US study that investigated the effect of different levels of physical activity on risk of death in older women (aged 72 on average).

To stay healthy, it's recommended that adults aged 65 and over do at least 150 minutes of moderate aerobic activity (such as cycling or brisk walking) every week, or 75 minutes of vigorous aerobic activity (such as running) every week, as well as strength exercises.

But it can be difficult for some older people to take part in these intense forms of exercise, so researchers wanted to see if light-intensity exercise, or even just less sedentary behaviour, would have the same health benefits.

The results suggested they didn't: light-intensity exercise, such as housework or gardening, was found to have no significant effect on risk of death.

But moderate to vigorous exercise had a better-than-expected effect on lowering death risk.

For women who recorded doing the highest levels of moderate to vigorous exercise, their risk of death was around 70% lower than women doing the lowest levels.

Bear in mind, though, that the study can't prove direct cause and effect. For example, it could be the case that people with poorer health (who were therefore already at higher risk of death) were less active.

Also, this isn't to say that light-intensity exercise doesn't have a positive effect on other health outcomes, such as heart health or mood.

Even if you don't feel able to meet the current recommended physical activity guidelines, the results of this study suggest that doing even a modest amount, such as regular brisk walking, may reduce the risk of death.

Where did the story come from?

The study was led by researchers from Harvard University in the US, and included researchers from several other institutions in the US and Japan.

It was funded by grants from the US National Institutes of Health.

The study was published in the peer-reviewed journal Circulation. It can be read for free online.

Generally, the Mail's coverage of this study was balanced, although claims made in the headline that one brisk walk a week could reduce the risk of early death by 70% isn't strictly accurate.

The 70% estimate only applied for people doing the highest levels of moderate to vigorous physical activity a day, compared with those who did the lowest levels.

For those who only did some moderate to vigorous activity (when compared with those who did no activity at all), the risk reduction was more around the 50 to 60% level.

What kind of research was this?

This prospective cohort study aimed to investigate the link between different levels of physical activity and sedentary behaviour, and risk of death in older women.

Prospective cohort studies like this one are useful for examining the influence of one thing (in this case, activity levels) on an outcome (in this case, death).

But the study design is limited in that it isn't possible to fully rule out the influence of other health and lifestyle factors, such as diet, and therefore can't confirm definite cause and effect.

What did the research involve?

The researchers used data from the Women's Health Study, one of the largest and longest-running observational women's health studies in the US, conducted at Harvard Medical School.

The women were all health professionals with an average age of 72 at baseline.

From 2011 to 2015, 18,289 women agreed to take part in the study, who represent about 60% of those eligible.

Participants were on average younger and healthier than those who chose not to take part.

The women were given a device called a triaxial accelerometer (ActiGraph GT3X+, ActiGraph Corp) and were asked to wear it on their hip for 7 days, except when sleeping or taking part in water-based activities.

The device is able to detect any activity levels, including light-intensity physical activity and sedentary behaviour.

Any deaths that occurred between 2011 and 2015 were recorded. The data was obtained from the US National Death Index.

The researchers examined associations between deaths and activity levels, looking at total physical activity, moderate to vigorous physical activity, low-intensity physical activity, and sedentary behaviour.

Researchers used a measuring scale, based on accelerometer technology, known as accelerometer vector magnitude counts per minute.

An AVM count provides an accurate measurement of physical activity by combining information about how fast someone is moving (acceleration) with how far they are moving (distance).

The higher the count per minute, the more vigorous the activity:

moderate to vigorous physical activity was categorised as equal to or more than 2,690 counts a minute
low-intensity physical activity as between 200 to 2,689 counts a minute
sedentary behaviour as less than 200 counts a minute

The findings were adjusted by age and the amount of time the participant reported wearing the device.

The second model was adjusted for confounding lifestyle factors, such as diet, smoking history and medication use.

What were the basic results?

The average time spent doing moderate to vigorous physical activity was 28 minutes a day, while low-intensity physical activity was 351 minutes a day, and sedentary behaviour was 503 minutes a day.

Average follow-up time was 2.3 years, during which 207 women died (1% of the study sample).

The highest quartile of each physical activity pattern or sedentary behaviour was compared with the lowest.

In the model fully adjusted for all confounders:

people with the highest total physical activity levels had 56% lower risk of dying than those with the lowest activity levels (hazard ratio [HR] 0.44, 95% confidence interval [CI]: 0.26-0.74)
there was also an even stronger association between moderate to vigorous physical activity and death from any cause, with the people doing the highest levels of moderate to vigorous physical activity showing a risk reduction of approximately 65% (HR 0.35, 95% CI: 0.20-0.61)
there was no significant association between levels of low-intensity physical activity and sedentary behaviour, specifically, and risk of death from all causes

How did the researchers interpret the results?

The researchers concluded: "The present study adds meaningfully to existing data because of its large sample size, use of triaxial accelerometer data, and investigation of a clinical outcome."

They say it supports current guidelines on moderate to vigorous physical activity, but doesn't support doing more low-intensity activity or decreasing sedentary behaviour to decrease risk.

Conclusion

The results of this study generally support current recommendations on moderate to vigorous physical activity, finding that higher levels were associated with a reduced risk of death in older women.

But increasing how much low-intensity physical activity older women do, or reducing their sedentary behaviour, doesn't lower this group's risk of death.

This was generally a large and well-conducted study, but there are a few points to note:

The study design can't prove definite cause and effect. Though the researchers have adjusted for several potential health and lifestyle confounders, it's difficult to ensure their effects have been fully accounted for.
Reverse causation is possible – it could be that people in poorer health (who were already at higher risk of death) were less active.
The study can't quantify an optimal amount of moderate to vigorous physical activity, or how this should be performed.
It also only looked at deaths from any cause. Although researchers found low-intensity physical activity and lower sedentary behaviour weren't associated with a reduced risk of death, it doesn't mean this type of exercise doesn't have other health benefits, such as for heart health.
The cohort was all older women, who were all health professionals. This makes it difficult to apply the findings to other groups. Health professionals could be generally healthier and adopt healthier habits than other people. And those who agreed to take part were already healthier than those who didn't.

To stay healthy, adults aged 65 and over should try to be active daily by doing:

at least 150 minutes of moderate aerobic activity, such as cycling or brisk walking, every week
strength exercises on 2 or more days a week that work all the major muscles (legs, hips, back, abdomen, chest, shoulders and arms)