Early smoking-onset age and risk of cardiovascular disease and mortality.
Early smoking onset age (SOA) is a public health concern with scant empirical evidence of its role in health outcomes. The study had two aims: i) to assess whether an early SOA was associated with the risk of fatal and non-fatal CVD and all-cause and CVD mortality and ii) to explore the linear and non-linear association between SOA and the outcomes of interest. Data from 4499 current or former smokers, recruited from 1995 to 2005, aged 25 to 79 years, and with a median 7.02 years of follow-up, were obtained from the REGICOR population-based cohort. In the present analysis, performed in 2018, the independent variable was SOA and the dependent variables were CVD events, CVD mortality, and all-cause mortality. Penalized smoothing spline methods were used to assess the linear and non-linear association. During follow-up, 361 deaths and 210 CVD events were recorded. A significant non-linear component was identified in the association between SOA and CVD outcomes with a cut-off point at 12 years: In the group aged ≤12 years, each year of delay in SOA was inversely associated with CVD risk (HR = 0.71; 95%CI = 0.53-0.96) and CVD mortality (HR = 0.58; 95%CI = 0.37-0.90). No association was observed in the older SOA group. A linear association was observed between SOA and all-cause mortality, and each year of delay was associated with 4% lower risk of mortality (HR = 0.96; 95%CI = 0.93-0.98). The associations were adjusted for lifelong exposure to tobacco and cardiovascular risk factors. These results reinforce the value of preventing tobacco use among teenagers and adolescents.