Association between long‐term low‐intensity cigarette smoking and incidence of smoking‐related cancer in the national institutes of health‐AARP cohort

An increasing proportion of US smokers smoke ≤10 cigarettes per day (CPD) or do not smoke every day, yet the health effects of low‐intensity smoking are poorly understood. We identified lifelong smokers of <1 or 1‐10 CPD and evaluated risk of incident cancer among 238,525 cancer‐free adults, aged 59‐82, in the NIH‐AARP Diet and Health Study. A questionnaire administered in 2004‐2005 assessed CPD during nine age‐periods (<15 to ≥70). We estimated hazard ratios (HR) and 95% confidence intervals (CI) using multivariable‐adjusted Cox proportional hazards regression with age as the underlying time metric. Of the 18,233 current smokers, (7.6%), 137 and 1,243 reported consistently smoking <1 CPD and 1‐10 CPD, respectively. Relative to never smokers, current smokers who reported consistently smoking 1‐10 CPD over their lifetime were 2.34 (95% CI = 1.86‐2.93) times more likely to develop smoking‐related cancer. Current lifetime smokers of <1 CPD were 1.89 (95% CI = 0.90‐3.96) times more likely to develop tobacco‐related cancer, although the association did not reach statistical significance. Associations were observed for lifelong smoking of ≤10 CPD with lung cancer (HR = 9.65, 95% CI = 6.93‐13.43); bladder cancer (HR = 2.22, 95% CI = 1.22‐4.05); and pancreatic cancer (HR = 2.03, 95%CI: 1.05‐3.95). Among lifelong ≤10 CPD smokers, former smokers had lower risks of smoking‐related cancer with longer time since cessation and longer smoking duration. Lifelong <1 and 1‐10 CPD smokers are at increased risk of incident cancer relative to never smokers and would benefit from cessation, providing further evidence that even low‐levels of cigarette smoking cause cancer.