But being sedentary for several hours a day linked to increased risk

Clear evidence that higher levels of physical activity - regardless of intensity - are associated with a lower risk of early death in middle aged and older people, is published by The BMJ today.

The findings also show that being sedentary, for example sitting still, for 9.5 hours or more a day (excluding sleeping time) is associated with an increased risk of death.

Previous studies have repeatedly suggested that sedentary behaviour is bad and physical activity is good for health and long life.

Guidelines recommend at least 150 minutes of moderate intensity or 75 minutes of vigorous physical activity each week, but are based mainly on self reported activity, which is often imprecise. So exactly how much activity (and at what intensity) is needed to protect health remains unclear.

To explore this further, researchers led by Professor Ulf Ekelund at the Norwegian School of Sport Sciences in Oslo analysed observational studies assessing physical activity and sedentary time with death ("all cause mortality").

Studies used accelerometers (a wearable device that tracks the volume and intensity of activity during waking hours) to measure total activity in counts per minute (cpm) of wear time. Intensity is usually separated into light, moderate and vigorous - and the time in these intensities is then estimated.

Examples of light intensity activity includes walking slowly or light tasks such as cooking or washing dishes. Moderate activity includes brisk walking, vacuuming or mowing the lawn, while vigorous activity includes jogging, carrying heavy loads or digging.

Data from eight high quality studies involving 36,383 adults aged at least 40 years (average age 62) were included. Activity levels were categorised into quarters, from least to most active, and participants were tracked for an average of 5.8 years.

During follow-up, 2149 (5.9%) participants died. After adjusting for potentially influential factors, the researchers found that any level of physical activity, regardless of intensity, was associated with a substantially lower risk of death.

Deaths fell steeply as total activity increased up to a plateau at 300 cpm, similar to the average activity levels in a population-based sample of US men and about 10-15% lower than that observed in Scandinavian men and women.

A similarly steep decrease in deaths occurred with increasing duration of light physical activity up to a plateau of about 300 minutes (5 hours) per day and of moderate intensity physical activity of about 24 minutes per day.

The largest reduction in risk of death (about 60-70%) was between the first quarter (least active) and the fourth quarter (most active), with approximately five times more deaths in those being inactive compared with those most active. This strengthens the view that any physical activity is beneficial and likely achievable for large segments of the population say the researchers.

In contrast, spending 9.5 hours or more each day sedentary was associated with a statistically significant increased risk of death.

The researchers point to some limitations. For example, all studies were conducted in the US and western Europe, and included adults who were at least 40 years old, so findings may not apply to other populations or to younger people.

Nevertheless, they say the large sample size and device based measures of sedentary time and physical activity provide more precise results than previous studies.

As such, they say their results provide important data for informing public health recommendations, and suggest that the public health message might simply be "sit less and move more and more often."

These findings are important and easy to interpret, say researchers in a linked editorial. However, questions remain, particularly over whether the effect of physical activity continues above a certain threshold.

They acknowledge that increasing activity at the population level is challenging, but say walking is one promising target for intervention, as it is simple, affordable (free), achievable even for older adults, and rarely contraindicated.

"Developing ways to limit sedentary time and increase activity at any level could considerably improve health and reduce mortality," they conclude.

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Peer-reviewed? Yes (research); No (linked editorial)

Evidence type: Systematic review and meta-analysis; Opinion

Subjects: People