Effects of Per- and Polyfluoroalkyl Substances (PFAS) Exposure Reduction on Serum Lipids in the Copenhagen City Heart Study: A Protocol for an Observational Cohort Study Emulating a Target Trial

Per- and polyfluoroalkyl substances (PFAS) are environmental contaminants associated with higher serum lipids, although primarily in cross-sectional studies, limiting causal inference. We aim to determine whether there is a causal relationship between PFAS and serum lipid levels by emulating a target trial of a hypothetical PFAS-reduction intervention using observational data. The target trial would enroll adults aged ≥20 years without prior cardiovascular, kidney, or liver disease, diabetes, or use of related medications. Participants would be randomly assigned to either PFAS-reduction counseling or no counseling, with adherence evaluated after 10 years, and then followed up after 10 years to assess effects on serum lipids. To emulate the target trial, we will use data from the Copenhagen City Heart Study on three successive clinical visits: baseline, follow-up, and outcome assessment visit, 10 years apart. Eligible participants meet the target trial criteria, have available blood samples for PFAS quantification at follow-up, and information on serum lipids at the outcome assessment. Intervention strategies will be evaluated based on observed reductions in PFAS concentrations between baseline and follow-up visit. Serum lipids are assessed at the outcome assessment visit. The emulation assumes exchangeability by adjusting for baseline and time-varying confounders using G-computation. This protocol explores applying the target trial emulation framework to improve causal inference in environmental epidemiology.