Background
The average life expectancy continues to increase in most of developed countries; however, this longevity does not necessarily translate in better health [
1]. The ageing phenomenon has led to a substantial increase in chronic conditions, which consequently result in a rising prevalence of multimorbidity, most commonly described as the presence of two or more long-term conditions [
2‐
4]. Multimorbidity has been linked to poor prognosis, lower quality of life [
5], increased health care costs, and the risk of premature death [
6]. Management of multimorbidity is a complex process, which recently has become an emerging priority for public health care professionals and health care systems [
7‐
9]. Physical activity (PA) has been recommended as one of the main lifestyle behaviours in the management of several chronic conditions worldwide [
10‐
12]. Yet, it is not clear whether and to what extent the benefits of PA apply to people with multimorbidity [
9].
To our knowledge, only two studies to date have assessed the relationship between PA and mortality in people with multimorbidity, with inconsistent findings. The first study showed that, in people with multimorbidity, high PA levels were related to a significantly lower risk of mortality, compared to being physically inactive [
13]. Conversely, the second study demonstrated that the risk of mortality was only significantly reduced when engaging in extremely high levels of PA (≥ 8000 moderate-vigorous PA MET-min/month), which may not be feasible for individuals with multimorbidity [
14]. Moreover, both studies used self-reported PA measures which have several limitations [
15]. For this reason, there is a need for accurate and reliable measures of PA [
16,
17]. Objective PA is capable of capturing precise estimates of energy expenditure at different activity intensities, in particular recording light PA [
18]. Yet, to date, no study has examined the association between objective PA and mortality in people with multimorbidity. Furthermore, the life expectancy according to PA levels and multimorbidity status remains not well determined.
We aimed to investigate the association between PA and all-cause mortality and to estimate the effects of PA on life expectancy in people with and without multimorbidity, using both subjective and objective measures of PA in a large contemporary cohort from the UK.
Discussion
We found an inverse dose-response association between PA and mortality in participants with and without multimorbidity, which persisted even after adjustments for sociodemographic and lifestyle factors. For self-reported PA, achieving volumes of PA that are consistent with the current guidelines of 150 min of moderate-intensity PA per week was associated with a longer life expectancy, with little additional benefit seen above this amount. Moreover, results for objectively measured PA suggested as little as 10 min of brisk walking a day was associated with a longer life expectancy, again with little additional benefit seen at higher categories.
Only two studies have assessed the relationship between self-reported PA and mortality in people with multimorbidity. The first study from Spain (
n = 3967), using LTPA, showed that in participants with multimorbidity (
n = 571), being physically active was related to a 35% (95% CI 16–50%) lower risk of mortality, compared to being inactive [
13]. Our results using LTPA mirror these findings, whereby there was a 35% lower risk in the high PA group compared to the low PA group. In contrast, results from the analysis of the National Health and Nutrition Examination Survey dataset (
n = 16,091) found that LTPA had a minimal effect on the multimorbidity-mortality relationship. The models were stratified by PA levels, and the number of chronic conditions was the exposure variable. Results showed that for each additional chronic condition, the association with mortality remained strongly significant, regardless of the amount of PA (i.e. stratifying by ≥ 4000 MVPA MET-min/month indicated for each additional chronic condition, there was a 22% higher risk of mortality). However, for those who performed ≥ 8000 MET-min/month, the multimorbidity-mortality relationship was much smaller (HR 1.08, 95% CI 0.87–1.33), suggesting that people with multimorbidity would gain a benefit only if they report extremely high levels of PA [
14]. Other studies in large general populations support our findings, as they show that both moderate and vigorous-intensity activities were associated with a longevity benefit [
32‐
34]. Although there are no studies that examine the comparative role of PA and multimorbidity on life expectancy, our results are in line with previous research based on different populations [
12,
34‐
36].
This study has some limitations. Firstly, participation in the UK Biobank was voluntary with slightly higher representation from affluent groups; therefore, the results may not be completely representative of the UK population [
37]. The sub-sample who undertook the objective PA measurements was relatively healthier than those who did not participate and was limited to only computer literate participants [
38]; this limits the representativeness of the sample for objective PA analysis, and these results should be interpreted with caution. Another limitation is related to the time difference between the baseline assessment and objective PA assessment: we analysed and adjusted for covariates at baseline (i.e. shifting the objective PA backwards), thus assuming the PA levels of the participants did not change between baseline and objective PA assessment, which may not be true. Nevertheless, objective PA measures have been used in a similar fashion in another UK Biobank analysis [
39]. Furthermore, data from a longitudinal study on older adults in England reported steady PA levels over time with a slight decline in the time spent in vigorous-intensity activities [
40]. Therefore, our results may have slightly under-estimated the association between objective PA and mortality. However, the hazard ratio results remained unchanged when we used the time of objective PA assessment as the start of the follow-up. Moreover, the short follow-up for the cohort of participants with objective PA did not allow a landmark analysis excluding participants who died in the first 2 years. There is currently no standard method for measuring multimorbidity [
41]; however, our definition included most of the core conditions for any multimorbidity measure [
7,
23,
25], and we have carried out sensitivity analyses using two different methods to ensure our findings are valid. Since this study was observational, we cannot derive any causality from the relationships we evidenced, yet there is substantial evidence supporting a causal relationship between higher levels of PA and good health status [
10,
11,
18,
34,
36]. Finally, although we found an association between PA and higher life expectancy, especially in people with multimorbidity, we were unable to assess whether this translates to a better quality of life.
Strengths of this study include the large sample size used to assess the association between PA with mortality and life expectancy by multimorbidity status. Also, this is the first study to use objective PA to assess its association with mortality in people with multimorbidity. We controlled for a wide range of important confounders, including age, as this is related to both PA and multimorbidity; however, we cannot completely exclude the potential for residual confounding. We also removed deaths occurring within the first 2 years at baseline to minimise the risk of reverse causality. We used three different measures of PA and three different multimorbidity definitions to ensure that the findings are robust. When accounting for the severity of the conditions, we found that the message was even stronger for those with a poor health rating and multimorbidity, or with top-10 comorbidity, because the benefits of physical activity had a much greater impact on the years of life gained compared to those who had a good health state or without top-10 comorbidity.
Conclusions
In conclusion, our findings showed an inverse dose-response association between PA and all-cause mortality suggesting the mortality benefits of PA still apply in people with multimorbidity. Moreover, our results indicated that self-reported levels of physical activity that are consistent with the current physical activity guidelines, or as little as 10 min of brisk walking a day based on objective measurement, were associated with longer life expectancy with little additional benefit observed above these levels, implying that it is not necessary to engage in high-volume or high-intensity PA to achieve the potential health benefits. However, we identified a large number of participants with multimorbidity who did not reach this level of PA, suggesting that there is a need for individuals with multimorbidity to increase their PA in ways that are achievable.
Acknowledgements
This research has been conducted using the UK Biobank Resource (Reference 14614).
We acknowledge the support from the National Institute for Health Research Collaboration for Leadership in Applied Health Research and Care - East Midlands (NIHR CLAHRC - EM), the Leicester Clinical Trials Unit, and the NIHR Leicester Biomedical Research Centre. The views expressed are those of the authors and not necessarily those of the NHS, the NIHR, or the Department of Health.
As part of the PhD, this study was selected to be presented at the following conferences: (1) CLAHRC East Midlands and North Thames Multimorbidity Collaboration Meeting 2017, Diabetes Research Centre, Leicester; (2) NIHR CLAHRC Cardiometabolic Research Day 2017, Stamford Court, Leicester; (3) Department of Health Sciences’ Annual Conference 2018, Stamford Court, Leicester; (4) National NIHR CLAHRC Multimorbidity Research Event 2018, Stamford Court, Leicester; (5) Trent Region Society for Academic Primary Care 2018, St Marys Conference Centre, Sheffield (awarded prestigious prize for the best presentation); (6) Public Health Research and Science Conference 2018, Public Health England, Warwick University, Warwick; (7) European Diabetes Epidemiology Group Annual Meeting 2018, Hotel Marienlyst, Elsinore, Denmark; (8) Health Sciences Postgraduate Forum 2018 (HeSPoF), College Court, Leicester; (9) Public Health England Research and Development Meeting 2018, East Midlands Centre, Seaton House, Nottingham; and (10) The UK Biobank Scientific Conference 2018 (abstract placed within the top 20 in the UK Biobank Early Career Researcher of the Year competition), QEII Conference Centre, London.