Nondaily smoking still tied to elevated cancer, mortality risk

People who smoke occasionally — even just a few times a month — still have a mortality risk significantly higher than never smokers, suggesting that complete cessation is needed to lower risks, according to a study published in JAMA Network Open.

Maki Inoue-Choi, PhD, MS, staff scientist in the metabolic epidemiology branch of the division of cancer epidemiology and genetics at the National Cancer Institute, and colleagues wrote that despite studies indicating that nondaily smoking is associated with elevated mortality, “there is a common perception among smokers that nondaily smoking poses little or no harm.”

Inoue-Choi and colleagues assessed the risk for all-cause and cause-specific mortality among daily smokers and nondaily smokers based on the number of cigarettes they smoke every month and years since they lowered their consumption from daily smoking or quit smoking.

They collected data from the NIH Tobacco Use Supplement to the Current Population Survey taken multiple years from 1992 to 2011 and linked those participants to responses from the National Longitudinal Mortality Survey.

After exclusions, 505,500 participants were included in the study and 47,000 deaths occurred.

The researchers found that daily smokers smoked a median of 600 cigarettes each month, nondaily smokers who had previously smoked daily had a median of 75 cigarettes each month and lifelong nondaily smokers smoked a median of 40 cigarettes each month.

Compared with never smokers, the risk for all-cause mortality was significantly higher among both current daily (HR = 2.32; 95% CI, 2.25-2.38) and lifelong nondaily (HR = 1.82; 95% CI, 1.65-2.01) smokers, despite the large difference in cigarette use between the groups.

Inoue-Choi and colleagues noted that an elevated risk for all-cause mortality association began with those who smoked just 6 to 10 cigarettes each month and increased with cigarette use.

The researchers determined that those who were nondaily smokers and had previously been daily smokers had lower mortality risks compared with daily smokers.

They also found that after 10 years of nondaily smoking, they had a similar a risk for all-cause mortality compared with never smokers to lifelong nondaily smokers (HR = 1.73; 95% CI, 1.56-1.92). However, these smokers had higher all-cause mortality risks compared with never smokers than those who had been daily smokers and had completely quit smoking for 10 or more years (HR = 1.18; 95% CI, 1.15-1.22).

Compared with never-smokers, Inoue-Choi and colleagues identified risks for smoking-related cancers that were 2.16 (95% CI, 1.64-2.86) times higher in lifelong nondaily smokers, 3.65 (95% CI, 3.11-4.27) times higher in nondaily smokers who had previously been daily smokers and 4.88 (95% CI, 4.57-5.22) times higher in daily smokers.

When specifically examining the risk for lung cancer, the researchers found that the hazard ratios compared with never smokers were 5.64 (95% CI, 3.89-8.18) in lifelong nondaily smokers, 10.22 (95% CI, 8.29-12.60) in nondaily smokers who had previously been daily smokers and 13.96 (95% CI, 12.50-15.59) in daily smokers.

“Our findings indicate that even very low levels of cigarette smoking are hazardous, supporting public health recommendations that there is no safe level of smoking and that all smokers, including nondaily and very low-intensity smokers, should quit,” Inoue-Choi and colleagues wrote.