This week's study is another population study. However, it's about walking, not nutrition.The study, conducted by Goldney et al, looked into the association between self-reported walking pace (SRWP) and cause-specific mortality over a decade using data from the UK Biobank.
The UK Biobank, initiated in 2006 and still ongoing, enrolled 503,317 individuals aged 40 to 69 between 2006 and 2010. Despite its massive scale, the response rate was only 5.5%. The study focused on 391,652 participants who were followed for an average of 12.6 years, excluding pregnant women and those recently diagnosed with cardiovascular disease (CVD) or cancer. The primary objective was to explore the links between SRWP and risks of cause-specific mortality, particularly cardiovascular disease, cancer, and other causes.
One fundamental flaw in the study was the reliance on self-reported walking pace, gathered through a touchscreen questionnaire. Approximately 6.6% claimed to be slow walkers, 52.6% identified as average-pace walkers, and 40.8% believed they were brisk walkers. Notably, the self-perceived 'average' skewed heavily toward being above average, highlighting a flaw in the study's baseline characteristics.
Table 1, the characteristics table, failed to appropriately separate data by walking pace. Instead, it divided them by sex, rendering the table irrelevant to the research question. Further, the small group comparator issue emerged, as the study heavily relied on the small group of slow walkers for comparison.
The supplementary file revealed stark differences among slow, average, and brisk walkers. Slow walkers tended to be older, with higher BMIs, lower physical activity, and a higher prevalence of smoking. Adjusting for these differences in statistical models could not account for the holistic health profile of individuals.
Over the 12.6-year follow-up, 22,413 deaths occurred, with brisk walkers displaying lower risk ratios for cancer, CVD, and other causes compared to slow walkers. However, these results were confounded by the healthier profile of brisk walkers.
The discussion section acknowledged the observational nature of the study and potential reverse causality, yet it failed to establish a clear mechanism linking brisk walking to lower mortality. While the paper suggested a connection between cardiorespiratory fitness and walking pace, it left many questions unanswered.
While I agree that SRWP may serve as a clinical predictive marker, I disagree with the notion that interventions to increase walking pace will extend longevity. The study exemplifies a common issue in population studies – mistaking the marker for the maker. Rather than walking pace influencing health, the study highlights that healthier individuals are more likely to walk briskly.