Introduction:
Exposure to secondhand smoke (SHS) is associated with an increase in mortality and morbidity. The aim of this work is to estimate the impact of the exposure to SHS on mortality in Spain in the population aged 35 and over in the year 2020.

Material and Methods:
Attributable mortality (AM) to SHS was estimated using a prevalence-dependent method. Prevalence of exposure was derived from a national representative crosssectional study and relative risks from metanalyses. AM estimations were accompanied by 95% confidence intervals (95%CI), which were calculated using a naive bootstrap procedure. AM, globally and by tobacco consumption, was estimated by sex, age group and cause of death. A sensitivity analysis was performed.

Results:
In Spain, in 2020, 747 (95% CI 676-825) deaths in the population aged 35 and over were attributed to exposure to SHS, 279 (95%CI 256-306) due to lung cancer and 468 (95% CI 417-523) due to ischemic heart disease. 75.1% of the AM occurred in men, 561 deaths (95% CI 494-634). 60.9% of deaths attributed to SHS exposure occurred in non-smokers. Including Chronic Obstructive Pulmonary Disease and stroke in the estimation rose the mortality burden to 2,242 deaths.

Conclusions:
Exposure to SHS is an important cause of death in Spain, associated with 1.5% of all deaths from lung cancer and ischemic heart disease in the population aged 35 and over. Most of the AM to SHS occurs in non-smokers. These data reinforce the need for health authorities to commit to reducing the exposure to SHS in any type of context and location.