A study has found that nondaily smokers have substantially higher mortality risks than never smokers, even if they smoke just a few cigarettes per month.

Cigarette smoking results in approximately 480,000 premature deaths in the United States each year, according to published reports. “Smoking behaviors among U.S. adults have changed over the past few decades,” explains Maki Inoue-Choi, PhD, MS. “While many smokers have quit, others have reduced their smoking. Now, many people smoke less than 10 cigarettes per day (low intensity) or on just some days of the month (nondaily).”

According to Dr. Inoue-Choi, there is a common perception among Americans that low-intensity and nondaily smoking poses little or no health risk. “However, accumulating evidence has demonstrated higher risks of death for low-intensity and nondaily smokers than never smokers,” she says. Published data indicate that lifelong nondaily smokers have a 1.7 times higher mortality risk and a 5-year shorter median life expectancy when compared with people who never smoke. “Many questions remain regarding the dose response of low-intensity and nondaily smoking with mortality,” adds Dr. Inoue-Choi.

New Research

For a prospective study published in JAMA Open Network, Dr. Inoue-Choi and colleagues assessed the risk of all-cause and cause-specific mortality in nondaily and daily cigarette smokers. Using harmonized data from multiple cycles of the Tobacco Use Supplements to the Current Population Survey from 1992-2011 that was linked to the National Death Index, the authors analyzed information on smoking patterns among more than 505,000 nondaily and daily cigarette smokers.

“We wanted to evaluate the risk of death by dose of smoking, which was measured by number of cigarettes smoked per month,” Dr. Inoue-Choi says. “We also wanted to assess the effect of reducing from daily to nondaily smoking and compare that with quitting. Providing information about the health risks of nondaily and low-intensity smoking can help smokers make informed decisions. It is also important for physicians to know about these studies so they can provide comprehensive information to their patients.”

Key Findings

In the study, daily smokers smoked a median of 20 cigarettes per day, whereas nondaily smokers typically smoked on 15 days of the month and smoked far fewer cigarettes per month than daily smokers. Lifelong nondaily smokers tended to be younger than daily smokers and nondaily, previous-daily smokers. When compared with daily smokers, participants identified as lifelong nondaily smokers were more likely to be from racial or ethnic minority groups. Current nondaily smokers were more likely to be college-educated than current daily smokers.

“A key finding from our study was that lifelong nondaily smokers had almost twice the risk of death as never smokers,” says Dr. Inoue-Choi. “Smoking as few as 6 to 10 cigarettes per month was associated with a higher risk of death than never smoking. Of note, the mortality risks were even higher among those who smoked more. Smokers who reduced from daily to nondaily smoking had lower mortality risks than daily smokers, but their risks remained higher than former and never smokers.” When compared with never smokers, the mortality risk among those who quit less than 2 years ago was similar to that of current daily smokers, whereas the lowest risk was observed among those who quit 10 or more years ago (Table).

Important Implications

“The most important message to take from our analysis is there is no safe level of smoking,” Dr. Inoue-Choi says. “The benefits of quitting are considerably larger than those of reducing from daily to non-daily smoking. Clinicians should encourage all smokers to quit, no matter how infrequently they smoke.”

Dr. Inoue-Choi notes that nondaily smoking has only recently become more common and therefore is a relatively new smoking pattern. “Future studies of the long-term patterns of nondaily smoking in the U.S. and other populations will be informative,” she says. “We are currently conducting larger studies to examine the health effects of smoking five or less cigarettes per month. We are also interested in learning more about the health risks of non-daily smoking in combination with other products such as cigars and e-cigarettes.”