November 21, 2018, 12:40 pm News Staff – An estimated 189 million adults worldwide smoke tobacco "occasionally" but not every day, yet few studies have examined the health risks of nondaily smoking.
Nondaily smokers account for a growing proportion of current smokers in the United States. In 2015, an estimated 8.9 million people in the United States were nondaily cigarette smokers, while the number of daily smokers decreased from 37 million in 2005 to 28 million in 2015.
A study published online in the American Journal of Preventive Medicine on Oct. 24 examined this topic and found that compared with never smokers, lifelong nondaily smokers had a 72 percent higher all-cause mortality risk. Nondaily smokers also had higher risks for cancer, heart disease and respiratory disease mortalities.
Researchers pooled data from the U.S. National Health Interview Surveys for 1991, 1992 and 1995 to create a nationally representative sample of more than 70,900 U.S. adults.
In addition to a thorough demographic breakdown, the surveys used for this study offered detailed cigarette smoking assessments, including days smoked in the past 30 days, number of cigarettes used on days smoked, and whether nondaily smokers had ever smoked daily, as well as linked mortality followup data.
This information permitted the researchers to determine that individuals characterized as nondaily smokers reported smoking a median of 15 days and 50 cigarettes per month in contrast to daily smokers, who smoked a median of 600 cigarettes per month.
The data also allowed the authors to examine the association of nondaily cigarette smoking with mortality throughout the age range and across racial/ethnic groups.
Additional information available from the surveys varied by survey year, including age at first trying cigarettes (1995 survey); age when starting to smoke regularly (1992 survey); number of days smoked in the past 30 days (all surveys); cigarettes used on days smoked (all surveys); number of months since last smoked daily (1991 and 1992 surveys); age at cessation (1992 and 1995 surveys); and number of years since cessation (1992 and 1995 surveys).
Mortality risks among nondaily smokers were assessed by number of days smoked in the past 30 days and number of cigarettes per days smoked among the 961 lifelong nondaily smokers who provided this information.
The NHIS is linked to mortality data through probabilistic record-matching with the National Death Index. Mortality risks through 2011 were identified using the NHIS-Linked Mortality Files.
Participants were followed from the date of interview through the date of death, the date before they turned age 96 or Dec. 31, 2011, whichever came first.
The median age of the 70,913 NHIS participants (29,943 men and 40,970 women) for whom data were analyzed was 41. Total participants broke down into 51 percent never smokers, about 23 percent former smokers and about 26 percent current smokers.
About 17 percent of current smokers were nondaily smokers, of whom about 65 percent said they had previously smoked daily and about 35 percent said they never smoked daily. Among former smokers, about 89 percent had ever smoked daily.
Compared with current daily smokers, current nondaily smokers were younger and more likely to belong to racial/ethnic groups other than non-Hispanic white and have higher educational achievement.
Researchers observed similar patterns when comparing current lifelong nondaily smokers with those who had previously smoked daily, as well as when comparing former never-daily smokers with former daily smokers.
Current nondaily smokers started smoking at a slightly older age than current daily smokers. Among current nondaily smokers, those who previously smoked daily smoked on more days in the past 30 days than lifelong nondaily smokers (15 versus 10 days).
The authors identified a total of 16,761 deaths through the end of 2011, including deaths from cancer (4,114); heart disease (3,830); cerebrovascular disease (1,121); respiratory disease (1,361); and other causes (6,335).
They also examined survival from age 18 to 95 by cigarette smoking status, with never smokers having a median survival of 85 years, lifelong nondaily smokers having a median of 80 years and daily smokers having a median of 75 years.
The researchers observed increased mortality risks among lifelong nondaily smokers, even at very low levels of cigarette use. Compared with never smokers, lifelong nondaily smokers' mortality risks based on the number of cigarettes they smoked per month were also higher: Those who smoked 11-30 cigarettes had a hazard ratio of 1.34, those who smoked 31-60 cigarettes had a 2.02 hazard ratio, and those who smoked more than 60 cigarettes had a hazard ratio of 1.74.
In comparison, daily smokers still had the highest mortality risks of the groups, with a hazard ratio of 2.5.
"As the number of nondaily smokers in this study was relatively small, future larger studies are needed to refine the associations, particularly among nondaily smokers using 30 or fewer cigarettes per month," the authors noted. "Yet, these findings provide additional evidence that even very low levels of smoking are hazardous and that all smokers, no matter how few cigarettes they smoke, should quit, as recommended by current guidelines."
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