Meeting minimum public health recommendations could prevent nearly one in two deaths linked to physical inactivity

Keeping physically active or becoming more active during middle and older age is associated with a lower risk of death, regardless of past activity levels or existing health conditions, suggests a large UK study published today by The BMJ.

The new findings indicate that at the population level, meeting and maintaining at least the minimum public health recommendations (equivalent to 150 minutes per week of moderate-intensity physical activity) would potentially prevent 46% of deaths associated with physical inactivity.

Previous studies have linked physical activity to lower risk of death, cardiovascular disease, and certain cancers, but few studies have examined if within-person changes in physical activity over time are associated with subsequent risk of death.

To address this knowledge gap, researchers from the MRC Epidemiology Unit at the University of Cambridge analysed data from 14,599 men and women aged 40-79 from the EPIC-Norfolk study to determine how long-term changes in physical activity are associated with risk of all-cause, cardiovascular and cancer deaths.

EPIC-Norfolk study participants were recruited between 1993 and1997. They were assessed at the start of the study, and then a further three times over an average of 7.6 years up to 2004. From this point in time, mortality was assessed up to 2016, for an average of 12.5 years of follow-up.

Physical activity was measured in each assessment using questionnaires and included activity at work (e.g. office work, standing work, physical and heavy manual work) and leisure-time activity, such as cycling, sports and recreational activities. These estimates were then converted to physical activity energy expenditure (PAEE) using combined movement and heart rate measurements from a validation study.

During the 12.5-year follow-up period, there were 3,148 deaths, including 950 deaths from cardiovascular disease and 1,091 deaths from cancer.

The researchers found that after controlling for established risk factors such as diet, body weight, medical history, blood pressure and cholesterol levels, both existing higher physical activity levels and increases in physical activity over time were associated with a lower risk of death.

For each 1kJ/kg/day per year increase in PAEE, which is equivalent to being inactive at the start of the study and gradually over five years meeting minimum physical activity guidelines, the researchers found a 24% lower risk of death from any cause, a 29% lower risk of cardiovascular death, and an 11% lower risk of cancer death. In addition to that, being active from the very beginning of the study conferred a 30% lower risk of all-cause mortality for a 10kJ/kg/day difference in baseline activity.

The results were similar in those with and without a history of cardiovascular disease and cancer. What’s more, compared with consistently inactive people, those who became more active over time had a lower risk of death from all causes, regardless of past activity levels.

The researchers also reported that the benefits were greatest for those with existing high levels of physical activity who became even more active over time, who had a 42% lower risk of mortality. There was no evidence of very high activity levels being harmful.

Alexander Mok, a PhD student at the MRC Epidemiology Unit and lead author of the study, says:

These results indicate that middle aged and older adults who are currently inactive, and those with existing cardiovascular disease and cancer, can still gain real longevity benefits by becoming more active. This is very encouraging, and underlines the broad public health benefits of physical activity.”

Senior author Dr Soren Brage, also at the MRC Epidemiology Unit, concludes:

Public health efforts should seek to maintain physical activity levels in people as they age, and specifically to prevent declines in middle age and beyond, in addition to efforts to shift the whole population towards meeting the minimum physical activity recommendations.”

This is an observational study, and as such can’t establish cause and effect, and the researchers point out that the sample was made up of people who were available for follow-up almost a decade after initial recruitment, who may not be entirely representative of the general population. However, this is a large study with long follow-up and repeat assessment that controlled for established risk factors, and the researchers say that the conclusions on change in activity would be robust to confounding from unmeasured factors that do not change over time, such as genetics or early-life exposures.

• Full paper: ‘Physical activity trajectories and mortality: population based cohort study’ by Mok et al. BMJ, 26 June 2019 . DOI: 10.1136/bmj.l2323
• The BMJ paper was reported in several national and international news outlets, including the Daily Mail, Sun, Telegraph, ITV News, Times of India, and ABC News, and Dr Brage was interviewed by Sky News Radio.