New research shows that any level of movement decreases risk of premature death, so get moving say Ulf Ekelund and Thomas Yates
It is well established that physical activity of a moderate or vigorous intensity (such as brisk walking) is good for your health.  More recently, it has also been shown that people in contemporary societies are spending the majority of their day sitting, and that this prolonged sitting is also linked to an increased risk for many chronic diseases and premature death. 
Current physical activity recommendations, including those recently updated for the US, suggest that at least 150 minutes per week of moderate intensity physical activity is needed to keep healthy and that prolonged sitting should be avoided. [3,4] However, how much sitting is too much? This is not specified and is widely debated. In addition, are levels of physical activity below those recommended still beneficial for health and does light intensity physical activity still count? Answering these questions have huge relevance for health promotion.
We performed a study to address these questions. To do this, we combined data from eight studies from the US, UK, and Scandinavia in which more than 36,000 participants wore a motion sensor (accelerometer) on a belt around their waist between four and seven days in total. Participants were followed for about six years, during which more than 2500 participants died. Given challenges around the General Data Protection Regulation with sharing individual participant data, not all the studies we included could be pooled. However, the authors of each included study re-analysed their accelerometer data to exactly the same criteria to ensure the measures of physical activity and sedentary behaviour were harmonised. Data from each study were then combined using meta-analytic techniques.
A key strength of this analysis was the use of physical activity monitors, which recorded all of the participants’ movements while the monitors were worn.  Most previous evidence underlying current physical activity recommendations are derived from data from large observational studies where people self-report how physically active they are (among other lifestyle behaviours). [3,4] Unfortunately, self-reported physical activity is prone to misreporting because people may often regard their levels of physical activity as higher than they actually are. The unhealthier the population, the more this misreporting tends to happen, which means that results are biased towards the null (no association). In addition, remembering the exact levels of physical activity undertaken across all domains of daily life (e.g. work, leisure, household) is challenging for everyone. This means that the exact amount and intensity of physical activity needed to reduce the risk of dying prematurely is still an unknown.
Our results suggest strong associations between total physical activity and the risk of dying. This finding was irrespective of the intensity of activity, meaning that increasing the total daily amount of physical activity through light intensity physical activity or moderate to vigorous physical activity substantially contributed to a lower risk of dying. The observation that light intensity physical activity also provided substantial health benefits is important for public health as this suggests that older people and those who are not able to be physically active at higher intensities will still benefit from just moving around.
The observed associations between physical activity and the risk of death were remarkably stronger than results previously observed when physical activity was assessed by participants self-reporting, confirming the effect of bias.  For example, the risk of dying was approximately 60% lower in the most active quarter compared with the least active quarter. If we express this in absolute numbers per 1,000 participants, 23 individuals died in the most active 25% of participants compared with 130 deaths per 1,000 participants in the least active 25%—more than a five-fold difference between groups.
While even doing small amounts of physical activity seemed to be associated with a reduced risk of dying prematurely, we also estimated how much time being physically active was associated with a maximally reduced risk. For moderate to vigorous intensity activity about 24 minutes per day (168 minutes per week) was associated with the greatest risk reduction. Doing more than this did not seem to lower the risk further. This is strikingly similar to the lower level of physical activity recommended by the most recent physical activity guidelines from the US. 
We also found that high amounts of sedentary time (e.g. sitting) above 9.5 hours per day was associated with an increased risk of death, whereas sitting levels below this threshold did not seem to be strongly linked to a difference in risk. Since sedentary behaviours and physical activity seem to be interrelated, a simple public health message would be to “sit less—move more and more often.”
Our analyses took a number of confounding factors that may influence these associations into account. We adjusted our analyses for sex, age, smoking, body mass index (a measure of obesity), and socioeconomic status. We also excluded individuals who died during the first two years of follow-up as including these individuals may have distorted the associations.
This is the largest study to date examining the associations between device measured physical activity and the risk of death. Additional strengths include the integrated approach we took in harmonising and reanalysing data from eight individual studies, and our estimates of the absolute amount of time in different intensities associated with the greatest benefits from physical activity.
However, as this is an observational study, we cannot infer a causal association between physical activity and the risk of death and our results are only applicable to middle aged and older individuals from high income countries. Future research including younger individuals and those from low and middle income countries are needed to confirm if our findings are generalisable to these populations.
Regardless, on a population level, the risks for an individual increasing or maintaining a physically active lifestyle are small, while the potential health benefits from these modest increases are substantial.
Ulf Ekelund is a professor at the Department of Sport Medicine, Norwegian School of Sport Sciences, Oslo and the Department of Chronic Diseases and Ageing, Norwegian Institute of Public Health, Oslo.
Competing interests: See research paper
Thomas Yates is a professor at the Diabetes Research Centre, College of Life Sciences, University of Leicester and the NIHR Leicester Biomedical Research Centre, University of Leicester.
Competing interests: See research paper
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