Daily 20-25 minutes of physical activity may reduce death risk from prolonged sitting

According to research published online in the British Journal of Sports Medicine, just 20-25 minutes of physical activity each day may be enough to offset the increased risk of death from a sedentary lifestyle.

But higher daily tallies of physical activity are linked to a lower risk, irrespective of the amount of time spent seated every day, the findings show.

In developed nations, adults spend an average of nine to ten hours every day sitting down--mostly during working hours. And a highly sedentary lifestyle is associated with a heightened risk of death, explain the researchers.

Much of the previously published research on the benefits of physical activity to counter prolonged sitting time has relied on aggregated data, which inevitably results in a broad brush approach, they suggest.

To try and overcome this, the researchers pooled individual participant data from four groups of people fitted with activity trackers to find out whether physical activity might modify the association between sedentary time and death, and vice versa, and what amount of physical activity and sitting time might influence risk.

They included Individual participant data from collected between 2003 and 2019 from the Norwegian Tromso Study 2015-16; the Swedish Healthy Ageing Initiative (HAI) 2012-19; the Norwegian National Physical Activity Survey (NNPAS) 2008- 09; and the US National Health and Nutrition Examination Survey (NHANES) 2003-06.

Just short of 12,000 people aged at least 50 were included in the analysis. They had a minimum of four days of 10 daily hours of activity tracker records, had been monitored for at least two years, and had provided details of potentially influential factors: their sex, educational level, weight, height, smoking history, alcohol intake, and whether they had current and/or previous cardiovascular disease, cancer and/or diabetes.

In all, 5943 people spent fewer than 10.5 hours sitting down every day; 6,042 clocked up 10.5 or more sedentary hours. Linkage with death registries showed that during an average period of 5 years, 805 (7 per cent) people died, 357 (6 per cent) of whom spent under 10.5 hours sitting down every day, and 448 of whom clocked up 10.5 hours or more.

The analysis of the activity tracker data showed that being sedentary for more than 12 hours a day was associated with a 38 per cent heightened risk of death compared with a daily tally of eight hours--but only among those totting up fewer than 22 daily minutes of moderate to vigorous physical activity.

More than 22 daily minutes of moderate to vigorous physical activity was associated with a lower risk of death.

While a higher amount of moderate to vigorous physical activity was associated with a lower risk of death, irrespective of the amount of sedentary time, the association between sedentary time and death was largely influenced by the amount of moderate to vigorous physical activity.

For example, an extra 10 minutes a day was associated with a 15 per cent lower risk of death in those spending fewer than 10.5 sedentary hours, and a 35 per cent lower risk among those spending more than 10.5 sedentary hours, every day.

Light intensity physical activity was only associated with a lower risk of death among highly sedentary people (12+ daily hours).

This is an observational study, and as such, can't establish cause and effect. And the researchers acknowledge that they weren't able to repeat measures of physical activity and sedentary hours, so precluding any changes in either over time.

Potentially influential factors, such as diet, mobility issues, and general health weren't accounted for either. And activity trackers may not correctly classify all activity types and their corresponding intensity--cycling, resistance exercises, gardening, for example.

Nevertheless, the researchers conclude: "Small amounts of MVPA [moderate to vigorous physical activity] may be an effective strategy to ameliorate the mortality risk from high sedentary time, where accumulating more than 22 minutes of MVPA eliminates the risk of high sedentary time.

"Efforts to promote physical activity may have substantial health benefits for individuals."