Sample and recruitment
heart or lung disease, infection
BLEEDING GUMS, INFECTION, RECRUITMENT
Participants were recruited in the Greater London (UK) area between March 2018 and February 2022, with a pause between March 2020 and September 2021 due to the COVID-19 pandemic, using various recruitment methods to access a diverse sample in terms of sociodemographic characteristics (age and sex). These included adverts in newspapers, social media, online NVP forums, approaching users on the street, email mailouts, as well as use of marketing companies.Participants were screened for eligibility via an online questionnaire. Inclusion criteria for the current study required participants to have smoked an average of five or more cigarettes per day for at least six months and not have regularly used NVPs or HTPs in their lifetime. Current smoking status was verified using a breathalyser to assess expired air carbon-monoxide (CO); readings above 8 ppm indicated current smoking. Due to collection of biological samples (as part of the wider study but not reported here), participants were excluded if they were younger than 18 years old, had a history of heart or lung disease, were pregnant, or had bleeding gums, illness, or infection within 24 h of their scheduled appointment. Forty-five participants were recruited, and this sample provided 90% power to detect medium effects (f = 0.25) for within group analyses. The power calculation was based on detecting effects for biological outcomes (not presented here) in cross-sectional analysis.The study received ethical approval from the University College London Ethics Committee (Project ID 12621/001). All methods were performed in accordance with the relevant guidelines and regulations. Informed consent was obtained from all subjects.