Sitting for over nine hours a day may up risk of early death: Study

Higher levels of physical activity -- regardless of intensity -- are associated with a lower risk of early death in middle aged and older people, a study claims.

The findings, published in the British Medical Journal (BMJ), also show that being sedentary, for example sitting for 9.5 hours or more a day -- excluding sleeping time -- is associated with an increased risk of death.

The World Health Organization (WHO) guidelines recommend at least 150 minutes of moderate intensity or 75 minutes of vigorous physical activity each week for adults aged between 18 and 64 years.

However, these 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.

Researchers led by Professor Ulf Ekelund at the Norwegian School of Sport Sciences in Oslo, Norway analysed observational studies assessing physical activity and sedentary time with death.

Studies included in the research used accelerometers -- a wearable device that tracks the volume and intensity of activity during waking hours -- to objectively measure daily activity levels.

Examples of light intensity activity include walking slowly or light tasks such as cooking or washing dishes. Moderate activity includes any activities that make you breath harder, such as brisk walking.

Data from eight high quality studies involved 36,383 adults aged at least 40 years with average age of 62.

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, 2,149 (5.9 per cent) 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 volume of physical activity increased up to a plateau of about 300 minutes (five hours) per day of light-intensity physical activity or about 24 minutes per day moderate intensity physical activity.

At these levels the risk of death was halved compared to those engaging in little or no physical activity.

"These results are fantastic. It has previously been widely assumed that more is better in terms of physical activity for health," said Tom Yates, a professor at the University of Leicester in the UK.

However, this study suggests health may be optimised with just 24 minutes per day of brisk walking or other forms of moderate-intensity physical activity.

"Another important finding was that spending 9.5 hours or more each day sedentary -- which essentially means sitting was associated with a statistically significant increased risk of death, with each hour more above this threshold increasing the risk of death further.

"This highlights the importance of avoiding spending most of the day sitting, as well undertaking purposeful physical activity," said Yates.

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.

They said the large sample size and device based measures of sedentary time and physical activity provide more precise results than previous studies.

"These findings really reinforce the saying 'Doing something is better than doing nothing'," said Charlotte Edwardson, an associate professor at the University of Leicester.

"Also, a large risk reduction was seen between the least and the second least active group suggesting that incorporating some time doing physical activity, light or moderate intensity, in daily life is associated with a big health benefit," said Edwardson.