BACKGROUND: Growing evidence demonstrates that there are health risks associated with non-daily smoking, but more work is needed to establish whether there is a dose-response, particularly with less frequent use.
METHODS: We assessed associations of non-daily smoking and all-cause and cause-specific mortality using data from 1,141,000 U.S. adults in the Tobacco Longitudinal Mortality Study (TLMS), a large nationally representative dataset from the Tobacco Use Supplement to the Current Population Surveys (TUS-CPS) with linked mortality data. Detailed information was collected in the TUS-CPS from 1992 to 2018 with mortality data through the end of 2019. We fit Cox proportional hazards regression models to estimate hazard risks (HRs) and 95% confidence intervals (CIs) for mortality outcomes, adjusting for potential confounders and survey year, including sampling weights for generalizability. Age at survey was used as the time metric.
RESULTS: After a mean follow-up of 13.3 years, mortality was higher among persons who smoked non-daily lifelong (HR=1.53, 95% CI=1.52–1.53) compared to those who never smoked, and when stratified by race/ethnicity in this non-daily group, mortality was higher among non-Hispanic Black individuals than their White counterparts. We observed a dose-response relationship in mortality risks by cigarettes per day (CPD) and month (CPM), across exposure from non-daily lifelong to daily smoking. Compared with people who never smoked, the mortality risk for all mortality among those who reported lifelong non-daily smoking was higher in the 1-2 CPM group (e.g., HR=1.14, 95% CI=1.11–1.18), with HRs increasing up to two-fold for those who smoked >90 CPM.
CONCLUSIONS: Non-daily smoking, regardless of whether participants reported lifelong non-daily smoking or prior daily use (not shown), is associated with increased all-cause and cause-specific mortality, with higher risk for 1-2 CPM and a dose-response relationship observed with higher CPM. Consistent with prior research, we observed increasing risks across the continuum of non-daily to daily smoking.