Physical activity across midlife and health-related quality of life in Australian women: A target trial emulation using a longitudinal cohort.

Background: There is little long-term causal evidence on the effect of physical activity on health-related quality of life. This study aimed to examine the associations between longitudinal patterns of physical activity over 15 years and health-related quality of life in both the physical and mental health domains, in a cohort of middle-aged Australian women. Methods and findings: We used data collected at 3-year intervals (1998 to 2019) from 11,336 participants in the Australian Longitudinal Study on Women's Health (ALSWH) (1946 to 1951 birth cohort). Primary outcomes were the physical (PCS) and mental health component summary (MCS) scores (range from 0 to 100; higher scores indicate higher perceived physical/mental health) from the SF-36 in 2019 (when women aged 68 to 73 years). Using target trial emulation to imitate a randomized controlled trial (RCT), we tested 2 interventions: (1) meeting the World Health Organization (WHO) physical activity guidelines consistently throughout the 15-year "exposure period" (2001 to 2016; when women aged 50–55 to 65–70 years; physical activity assessed every 3 years); and (2) not meeting the guidelines at the beginning of the exposure period but starting to first meet the guidelines at age 55, 60, or 65; against the control of not meeting the guidelines throughout the exposure period. Analysis controlled for confounding using marginal structural models which were adjusted for sociodemographic and health variables and conditions. Consistent adherence to guidelines during the exposure period (PCS: 46.93 [99.5% confidence interval [CI]: 46.32, 47.54]) and first starting to meet the guidelines at age 55 (PCS: 46.96 [99.5% CI: 45.53, 48.40]) were associated with three-point higher PCS (mean score difference: 3.0 [99.5% CI: 1.8, 4.1] and 3.0 [99.5% CI:1.2, 4.8]) than consistent non-adherence (PCS: 43.90 [99.5% CI: 42.79, 45.01]). We found a similar pattern for most SF-36 subscales but no significant effects of the interventions on MCS. The main limitations of the study were that it may not account for all underlying health conditions and/or other unmeasured or insufficiently measured confounders, the use of self-reported physical activity and that findings may not be generalizable to all mid-age women. Conclusions: Results from the emulated RCT suggest women should be active throughout mid-age, ideally increasing activity levels to meet the guidelines by age 55, to gain the most benefits for physical health in later life. Binh Nguyen and colleagues, use longitudinally collected data and target trial emulation methods to explore the impact of mid-life physical activity on the health outcomes of Australian women later in life. Author summary: Why was this study done?: ○ The evidence for an association between physical activity and health-related quality of life has been based primarily on cross-sectional studies and randomized controlled trials (RCTs) with short-term outcomes. ○ To date, few longitudinal studies have examined the associations between long-term patterns of physical activity and health-related quality of life, measured physical activity at more than one time point, and examined the causal effects of physical activity. What did the researchers do and find?: ○ We leveraged data on >11,000 women enrolled in the Australian Longitudinal Study on Women's Health (ALSWH) and applied targeted maximum likelihood estimation (TMLE) to emulate various target trials of physical adherence regimes and explore how physical activity in midlife impacts health outcomes in later life. ○ We found that consistent adherence to physical activity guidelines over 15 years was associated with better health-related quality of life in the physical health domain, especially physical functioning. ○ Meeting physical activity guidelines earlier in midlife and especially by age 55 resulted in better physical health-related quality of life outcomes in later life but the same impact on mental health domain outcomes was less evident. What do these findings mean?: ○ This study provides insights into the long-term effects of different patterns of physical activity during mid-age on later health-related quality of life in Australian women. ○ Combined with existing evidence, it contributes to the growing evidence concerning the benefits of maintaining or adopting an active lifestyle in mid-age. ○ The study presents an important message for public health which encourages women to be active throughout mid-age, even if they start meeting physical activity guidelines in their mid-50s, to gain the most benefits for physical health-related quality of life latterly. ○ Limitations of the study included reliance on self-reported physical activity, an inability to account for all contributing factors and findings may not be generalizable to all mid-age Australian women or to women outside of Australia. [ABSTRACT FROM AUTHOR]