Dose-Response Association of Low-Intensity and Nondaily Smoking With Mortality in the United States

IMPORTANCE An increasing proportion of US smokers smoke at low intensity and not every day. Some nondaily smokers have always had this pattern, whereas others previously smoked daily. The effect of reducing the level of smoking from daily to nondaily smoking and the dose response at low smoking levels are poorly understood. OBJECTIVE To evaluate risk of all-cause and cause-specific mortality among nondaily and daily cigarette smokers, by cigarettes per month, years after reducing from daily to nondaily smoking, and years since quitting. DESIGN, SETTING, AND PARTICIPANTS A prospective cohort study using harmonized data from multiple cycles of the Tobacco Use Supplements to the Current Population Survey (TUS-CPS), linked totheNationalDeathIndex,wereanalyzedduringtheperiodfrom2018to2020.Adultscompleted the 1992-1993, 1995-1996, 1998-1999, 2000, 2001-2002, 2003, 2006-2007, or 2010-2011 TUS-CPS. Cigarette smokers were classified as daily or nondaily users; current nondaily smokers were further categorized by whether they previously smoked every day. MAIN OUTCOMES AND MEASURES Hazard ratios (HRs) and 95% CIs for risks of mortality vs never smoking.Agewastheunderlyingtimemetric,adjustedforsex,race/ethnicity,education,surveyyear, and household income. RESULTS Among 505500 participants (aged 18-103 years), approximately 47000 deaths occurred. The median number of cigarettes smoked per month was 600 (interquartile range, 300-600) (20 cigarettes per day [interquartile range, 10-20 cigarettes per day]) for daily cigarette smokers and 40 (interquartile range, 15-90) for lifelong nondaily smokers. Nevertheless, both current daily (HR, 2.32; 95% CI, 2.25-2


Introduction
Cigarette smoking results in an estimated 480 000 premature deaths in the United States and 7 million deaths worldwide each year. 1,2In the US, the prevalence of cigarette smoking has decreased dramatically owing to a wide range of public health programs.In 2018, 13.7% of US adults (34.2 million) smoked cigarettes, a 34.4% decrease from 2005 (20.9% [45.1 million adults]). 3,4 addition to the decreasing prevalence of smoking, an increasing number of smokers smoke at low intensity (<10 cigarettes per day) or on just some days of the month (nondaily).Among US current smokers who reported smoking in the past 30 days, the proportion of nondaily smokers increased from 19.2% in 2005 to 25.0% in 2018. 3,4The proportion of low-intensity daily smokers also increased, from 16.4% in 2005 to 25.0% in 2016. 3Nondaily smokers may differ substantively from daily smokers, both with regard to nicotine dependence and in reasons for smoking. 5,6In light of continued policy, regulatory, and societal changes and the emergence of other tobacco products, the numbers of occasional and low-intensity cigarette smokers are expected to increase.
There is a common perception among smokers that nondaily smoking poses little or no harm. 7vertheless, emerging studies indicate that lifelong nondaily smokers have an approximately 1.7 times higher mortality risk and a 5-year shorter median life expectancy compared with never smokers. 8Nondaily smokers also benefit from smoking cessation. 8Numerous questions remain, however.Among nondaily smokers, the dose reponse is poorly understood.The association of changing from daily to nondaily smoking with mortality is also unknown.Such data will inform the potential contribution of nondaily smoking to the worldwide tobacco epidemic.
To answer these key questions, we harmonized multiple cycles of the Tobacco Use Supplement to the Current Population Survey (TUS-CPS) linked to the National Longitudinal Mortality Survey (NLMS), leveraging detailed information on smoking patterns among both nondaily and daily cigarette smokers with a large US representative sample size.

Study Population
The TUS-CPS is a National Cancer Institute/National Institutes of Health-sponsored national survey The TUS-CPS is a cross-sectional survey, 9 but a subset of the TUS-CPS has been linked to mortality data from the National Death Index (currently through 2011), as part of the NLMS.The NLMS consists of US Census Bureau data from the CPS and Annual Social and Economic Supplements that have been linked with death certificate data.The present analysis includes the subset of participants in the NLMS who completed the TUS surveys.
The human subject internal review board of the National Institutes of Health determined this study to be exempt because data are not identifiable.All analyses were performed by a statistician of the US Census Bureau during the period from 2018 to 2020.We rounded all weighted and unweighted numbers following the disclosure avoidance guidelines by the US Census Disclosure Review Board to protect study participants' confidentially.This study is reported according to the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline.

Tobacco Use
We combined tobacco use data from the 1992-1993, 1995-1996, 1998-1999, 2000, 2001-2002,   2003, 2006-2007, and 2010-2011 TUS-CPS questionnaires into a single data set for analyses.From approximately 705 000 individuals in the TUS-CPS NLMS linked data from these years, we excluded 34 000 who died before the start of follow-up or were not eligible for mortality linkage, 131 000 who reported having smoked less than 100 cigarettes in their lives, 1000 with incomplete smoking information, and 8300 with unknown race/ethnicity.We also excluded individuals who were younger than 18 years of age or older than 103 years of age because smoking-related deaths are unlikely to occur at very old ages and to exclude extreme survivors.After these exclusions, the analysis included approximately 505 500 individuals.
We defined ever cigarette smokers as individuals who reported smoking 100 cigarettes or more in their lives.Current smokers reported smoking cigarettes in the past 30 days, either every day (daily smokers) or on some days of the month (nondaily smokers).Nondaily smokers were stratified into those who previously smoked daily (nondaily, previous-daily smokers) and those who never smoked daily (lifelong nondaily smokers).We categorized former smokers, who reported not smoking in the past 30 days, into former daily smokers and former nondaily smokers.
We assessed detailed smoking patterns, including number of days smoked in the past 30 days, number of cigarettes smoked on days smoked, age started smoking, and age at cessation.We computed the number of cigarettes smoked per day or in the past 30-day month and categorized current daily smokers (Յ1, >1-2, >2-10, >10-20, >20-30, and >30 cigarettes per day) and nondaily smokers (Յ5, 6-10, 11-30, 31-60, and >60 cigarettes per month).We stratified current nondaily smokers who had previously smoked daily by number of years since reducing the level of smoking from daily to nondaily (<2, 2-9, and Ն10 years).We also stratified former daily and nondaily smokers by number of years since cessation (<2, 2-4, 5-9, and Ն10 years).Never cigarette smokers were the referent group in all analyses.

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Relevant NLMS sampling weights were set to the noninstitutional US population size, appropriately accounting for the cluster sampling design of the original surveys.We reweighted sampling weights for differences in cohort size and incorporated in all models.
We performed a sensitivity analysis for all-cause mortality excluding participants who reported ever using other tobacco products (cigar, pipe, and smokeless tobacco).We conducted all analyses using Unix SAS, version 9.4 (SAS Institute Inc), 2-tailed statistical tests, and P < .05 as the threshold for statistical significance.
Nondaily smokers typically smoked on 15 days (IQR, 6-20 days for lifelong nondaily smokers; IQR, 10-20 days for nondaily, previous-daily smokers) of the month and smoked far fewer cigarettes per month than daily smokers (lifelong nondaily smokers: 40 cigarettes per month [IQR, 15-90 cigarettes per month]; nondaily, previous-daily smokers: 75 cigarettes per month [IQR, 30-150 cigarettes per month]).Nondaily and daily smokers both started smoking at a median age of 17 to 18 years.Among never cigarette smokers, 8.1% reported ever using other tobacco products (cigar, pipe, and smokeless tobacco), whereas approximately 20% to 23% of current cigarette smokers reported ever using other tobacco products.E-cigarettes and similar devices were not assessed in the surveys included in this analysis.
Nondaily smoking was associated with a number of different causes of death ( Among lifelong nondaily smokers, mortality risks increased in association with higher numbers of cigarettes per month (Figure 1).The HRs (95% CIs) for all-cause mortality were 1.18 (0.79-1.75) for 5 or less cigarettes per month, 1.80 (1.23-2.64)for 6 to 10 cigarettes per month, 1.56 (1.24-1.96)for 11 to 30 cigarettes per month, 1.91 (1.49-2.44)for 31 to 60 cigarettes per month, and 2.16 (1.83-2.54)for more than 60 cigarettes per month.A similar dose-response association was observed among current daily smokers, with increased risk observed even at less than 1 or 1 cigarette per day (HR, 2.23; 95% CI, 1.67-2.96).Current daily smokers who smoked more than 30 cigarettes per day had still higher mortality risks (HR, 2.94; 95% CI, 2.75-3.14).We also observed a shorter median survival with a higher number of cigarettes per month and per day among lifelong nondaily smokers and current daily smokers, respectively (Figure 1).
Figure 2 depicts the mortality risks of reducing the level of smoking from daily to nondaily.A dose-dependent association was observed, whereby the lowest risk was observed among respondents who reduced their level of smoking from daily to nondaily 10 or more years ago (HR, Table 1.Demographic Characteristics and Cigarette Smoking Patterns by Smoking Status Among 505 500 Adults in the 1992-1993, 1995-1996, 1998-1999, 2000,  2001-2002, 2003, 2006-2007, and

Discussion
In a large nationally representative study, we observed that low-intensity and nondaily smoking was associated with substantially higher mortality risks than never smoking.Although mortality decreased for smokers who reduced their level of smoking from daily to nondaily, the benefits of cessation were far greater.Our analysis also provides insight into the dose response of low-intensity smoking.We observed increased mortality risks among nondaily smokers who smoked just 6 to 10 cigarettes per month, well under 1 cigarette per day, with higher mortality risks among those smoking additional amounts.The magnitude of these associations suggest that even lower levels of smoking may be associated with risk.Future studies with larger numbers of very low-intensity smokers will be informative.
The large sample size allowed us to systematically compare 2 groups of nondaily smokers.
c Unweighted numbers were rounded following the disclosure avoidance guidelines by the US Census Bureau's DRB: if the number is less than 15, report it; if the number is between 15 and 99, round to the nearest 10; if the number is between 100 and 999, round to the nearest 50; if the number is between 1000 and 9999, round to the nearest 100; if the number is between 10 000 and 99 999, round to the nearest 500; if the number is between 100 000 and 999 999, round to the nearest 1000; and if the number is 1 000 000 or more, round to 4 significant digits.Lifelong nondaily smokers tended to be younger and smoke fewer cigarettes per month than those who had previously smoked every day, although both groups tended to have started smoking in their teenage years.b Adjusted for sex, race/ethnicity (non-Hispanic white, non-Hispanic black, Hispanic, and non-Hispanic other), education (<high school, high school, some college, and college), survey year (1992-1993, 1995-1996/1998-1999, 2000/2001-2002, 2006-2007, and  2010-2011), and ratio of standardized income to the poverty level (<50%, 50% to <100%, 100% to <200%, 200% to <400%, Ն400%, and missing).

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c Unweighted numbers were rounded following disclosure avoidance guidelines by the US Census Bureau's DRB: if the number is less than 15, report it; if the number is between 15 and 99, round to the nearest 10; if the number is between 100 and 999, round to the nearest 50; if the number is between 1000 and 9999, round to the nearest 100; if the number is between 10 000 and 99 999, round to the nearest 500; if the number is between 100 000 and 999 999, round to the nearest 1000; and if the number is 1 000 000 or more, round to 4 significant digits.c Adjusted for sex, race/ethnicity (non-Hispanic white, non-Hispanic black, Hispanic, and non-Hispanic other), education (<high school, high school, some college, and college), survey year (1992-1993, 1995-1996/1998-1999, 2000/2001-2002/2003, 2006-2007, and 2010-2011), and ratio of standardized income to the poverty level (<50%, 50% to <100%, 100% to <200%, 200% to <400%, Ն400%, and missing).We were also able to investigate the association of reducing the level of smoking from daily to nondaily with mortality risks.Daily smokers who became nondaily smokers substantially reduced their monthly cigarette consumption, and their subsequent mortality risks decreased to those of lifelong nondaily smokers after 10 years of reduction.Nevertheless, their mortality risks remained substantially greater than both never and former smokers.Thus, our study provides important evidence on the benefits of smoking cessation beyond even substantial reductions in cigarette smoking.

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Previous studies on the disease and mortality risks of nondaily cigarette smoking have been limited but are generally consistent with our findings.In a previous analysis of TUS-CPS NLMS data, current nondaily cigarette smokers had 1.60 times (95% CI, 1.52-1.69)higher all-cause mortality than never smokers. 10Similarly increased risks of all-cause mortality were reported among current occasional smokers in cohort studies in Finland (HR, 1.As observed in the present study as well as previously, the strongest associations for cigarette smoking among both nondaily and daily smokers were observed for deaths from lung cancer and respiratory disease, with weaker but still important associations observed for deaths from cardiovascular and other diseases. 1,8,13,14

Strengths and Limitations
The most important strength of the present study is the detailed data on cigarette smoking patterns, which enabled the identification of lifelong nondaily smokers and the assessment of the mortality risks of reducing the level of smoking from daily to nondaily.We were also able to perform a sensitivity analysis excluding ever users of other tobacco products.Large sample size and nationally representative sample are also key strengths.With data collected from more than 500 000 adults, we were able to evaluate a dose-response association across detailed categories of number of cigarettes per month among lifelong nondaily smokers.Appropriate survey weights were applied so that findings from this study are representative of the US civilian, noninstitutionalized adult population.
The present study also has limitations.Cigarette smoking was assessed at 1 time point; therefore, smoking status may have changed during the follow-up.We relied on participants recalling their smoking, and approximately 20% of the questionnaires were completed by proxies.Thus, there is potentially recall bias. 157][18] The surveys included in our study did not assess e-cigarette use; therefore, we were unable to examine the mortality risks of nondaily cigarette smokers who additionally use e-cigarettes and compare them with those who did not use e-cigarettes.Regarding other tobacco products, we restricted our sensitivity analysis to exclusive nondaily smokers who did not use pipe, cigar, or smokeless tobacco and found little change.Our study also lacked information on certain potential confounders, such as diet, physical activity, and medical history.However, the adjustment for physical activity or diet did not affect the association between smoking and mortality considerably in previous studies. 8,19Nevertheless, uncontrolled and residual confounding are potential limitations, as in any observational studies.
Nondaily smoking is more common among non-Hispanic black and Hispanic individuals than non-Hispanic white individuals.We found generally similar associations for daily and nondaily smoking across examined racial/ethnic groups; although our study is large, our sample size was Reflecting the US population, daily and nondaily smokers started smoking as teenagers in our study.Thus, observed mortality risks are for long-term daily and nondaily smokers.Because smoking duration, independent of intensity, is a particularly important determinant of disease risk, [20][21][22] studies of nondaily smoking in other populations where people initiate smoking at older ages will also be

Conclusions
In this nationally representative study, both daily and nondaily smokers had substantially higher mortality risks than never smoking.Associations were observed among daily smokers who smoked 1 cigarette per day and among nondaily smokers who smoked 6 to 10 cigarettes per month, with risks among both groups increasing with greater use.Furthermore, the mortality risks of daily smokers who substantially reduced their cigarette consumption to become nondaily smokers decreased but remained elevated.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.
for tobacco use, administered as part of the US Census Bureau's Current Population Survey every few years since 1992-1993.The US Centers for Disease Control and Prevention cosponsored the 2001-2002, 2003, and 2006-2007 waves, and the US Food and Drug Administration, Center for Tobacco Products cosponsored the 2014-2015 and 2018-2019 waves.In each cycle, approximately 240 000 adults in eligible households among the civilian, noninstitutionalized US population received questionnaires.Approximately 64% of respondents completed the questionnaire by telephone, and approximately 36% completed the questionnaire via in-person interviews.

Figure 1 .A 5 0Ca
Figure 1.All-Cause Mortality Risk and Survival by Number of Cigarettes Smoked per Month (30 Days) or per Day

Figure 2 .
Figure 2. All-Cause Mortality Risk and Survival by Years Since Reducing From Daily to Nondaily Smoking Among Current Nondaily, Ever-Daily Smokers relatively low for certain comparisons, such as mortality risks of lifelong nondaily smoking among JAMA Network Open | Public Health Associaton of Low-Intensity and Nondaily Smoking With Mortality JAMA Network Open.2020;3(6):e206436.doi:10.1001/jamanetworkopen.2020.6436(Reprinted) June 3, 2020 9/11 Downloaded From: https://jamanetwork.com/ on 10/08/2023Hispanic individuals.Future studies will inform us with the long-term patterns of nondaily smokers in the US population and possible differences by race/ethnicity, sex, and birth cohort.

Table 3 .
All-Cause Mortality Risk by Years Since Cessation Among Former Daily and Nondaily Smokers Compared With Risk Among Never Smokers a Unweighted numbers were rounded following the disclosure avoidance guidelines by the US Census Bureau's DRB: if the number is less than 15, report it; if the number is between 15 and 99, round to the nearest 10; if the number is between 100 and 999, round to the nearest 50; if the number is between 1000 and 9999, round to the nearest 100; if the number is between 10 000 and 99 999, round to the nearest 500; if the number is between 100 000 and 999 999, round to the nearest 1000; and if the number is 1 000 000 or more, round to 4 significant digits. b Associaton of Low-Intensity and Nondaily Smoking With Mortality Downloaded From: https://jamanetwork.com/ on 10/08/2023