International journal of epidemiology最新文献

Background: Cohort studies are instrumental in examining long-term risks associated with environmental exposures but require appropriate control for various confounding effects. In this contribution, we assessed this issue by investigating the relationship between fine particulate matter (PM2.5) exposure and mortality in a UK-based cohort.

Methods: We analysed data from half a million adults in the UK Biobank linked with time-varying individual-level exposure data and followed up during the period 2006-21. The assessment focused on confounding related to spatial and temporal patterns as well as due to measurable variables, including both contextual and individual-level factors. We performed an evaluation consisting of descriptive analyses, specification and interpretation of direct acyclic graphs (DAGs), and comparison of results from survival models.

Results: We found correlations between PM2.5 exposure and mortality rates across time, geographical areas, and categories of measurable variables. The DAG indicated complex causal pathways and the need to adjust for a wide set of potential confounders. The regression analysis confirmed these patterns: the fully adjusted model estimated a hazard ratio (HR) of 1.25 (95% CI: 1.06-1.49) per 10 μg/m3 increments in PM2.5, but the association reversed to 0.82 (0.76-0.87) when excluding control for recruitment centre, suggesting strong spatial confounding. Calendar time showed stronger confounding effects compared to age. Area-level socio-economic indicators were more important than individual-level counterparts, while lack of control for lifestyle factors led to a noticeable overestimation.

Conclusions: This case-study illustration elucidates various confounding mechanisms in cohort studies on environmental risks and offers a critical evaluation of alternative adjustment strategies.

Background: Greenspace has been linked to reduced mortality while air pollution has been associated with increased mortality. We examined whether the joint association of greenspace and air pollution on mortality varies across ages, sexes, educational levels, urban and rural environments, and differential levels of both exposures in a nationwide population of Finland.

Methods: This study utilized routinely collected individual-level register data from Statistics Finland encompassing all citizens aged 30 years or older in 2000 (N = 3 003 519), followed until 2019. Greenspace was measured using the Enhanced Vegetation Index (EVI), and air pollution by the concentration of fine particulate matter ≤2.5 µm (PM2.5). Cox proportional hazards models were used to assess linear and non-linear associations between EVI, PM2.5, and mortality. Age was modeled flexibly with a natural cubic spline with four knots. Analyses were stratified by sex, educational level, and urbanicity.

Results: Both EVI and PM2.5 were independently associated with mortality (EVI: HR 0.99; 95% CI: 0.98-0.99 per IQR; PM2.5: HR 1.02; 95% CI: 1.01-1.03), with evidence of an interaction between the two (EVI × PM2.5: HR 0.99; 95% CI: 0.99-0.99). The joint association varied across age, sex, education, urbanicity, and the level of both exposures. PM2.5 was primarily linearly associated with increased mortality, accounting for EVI. In contrast, the relationship between EVI and mortality was less linear and more variable.

Conclusions: Expanding greenspace may be most beneficial in areas where it is limited and where air pollution levels are high.