Background Little is known about the health harms associated with low-intensity smoking in Asians who, on average, smoke fewer cigarettes and start smoking at a later age than their Western counterparts.
Methods In this pooled analysis of 738 013 Asians from 16 prospective cohorts, we quantified the associations of low-intensity (<5 cigarettes/day) and late initiation (≥35 years) of smoking with mortality outcomes. HRs and 95% CIs were estimated for each cohort by Cox regression. Cohort-specific HRs were pooled using random-effects meta-analysis.
Findings During a mean follow-up of 11.3 years, 92 068 deaths were ascertained. Compared with never smokers, current smokers who consumed <5 cigarettes/day or started smoking after age 35 years had a 16%–41% increased risk of all-cause, cardiovascular disease (CVD), respiratory disease mortality and a >twofold risk of lung cancer mortality. Furthermore, current smokers who started smoking after age 35 and smoked <5 cigarettes/day had significantly elevated risks of all-cause (HRs (95% CIs)=1.14 (1.05 to 1.23)), CVD (1.27 (1.08 to 1.49)) and respiratory disease (1.54 (1.17 to 2.01)) mortality. Even smokers who smoked <5 cigarettes/day but quit smoking before the age of 45 years had a 16% elevated risk of all-cause mortality; however, the risk declined further with increasing duration of abstinence.
Conclusions Our study showed that smokers who smoked a small number of cigarettes or started smoking later in life also experienced significantly elevated all-cause and major cause-specific mortality but benefited from cessation. There is no safe way to smoke—not smoking is always the best choice.
- smoking caused disease
- socioeconomic status
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Contributors WZ conceived, designed and supervised the study. JJY, DY, X-OS, NDF, WW and WZ contributed to data analysis, data interpretation and writing the manuscript. X-OS, SR, SKA, ES, PCG, JH, ST, Y-TG, Y-BX, J-MY, YT, IT, YS, KM, Y-OA, SKP, YC, W-HP, MP, DG, NS, HC, H-LL, W-PK, RW, SZ, SK, HI, M-HS, P-EW, K-YY, HA, KSC, PB, MI, DK, JDP and WZ contributed to data collection and provided study materials and administrative/technical support. All authors contributed to critical revision of the manuscript for important intellectual content and approved the final version of the manuscript.
Funding This work was supported by research funds from the Anne Potter Wilson Chair endowment and National Institutes of Health grants (UM1CA182910 to Dr Zheng and UM1CA173640 to Dr Shu) at Vanderbilt University Medical Center. Participating cohort studies (funding sources) in the consortium are: China National Hypertension Survey Epidemiology Follow-up Study (CHEFS, funding sources: American Heart Association (9750612N), NHLBI (U01-HL072507), Chinese Academy of Medical Sciences); Shanghai Cohort Study (SCS, funding sources: NIH (R01CA0403092, R01CA144034, UM1CA182876)); Shanghai Men’s Health Study (SMHS, funding sources: NIH (R01-CA82729)); Shanghai Women’s Health Study (SWHS, funding sources: NIH (R37-CA70867)); Korea Multicenter Cancer Cohort (KMCC, funding sources: Ministry of Education, Science and Technology, Korea, National Research Foundation of Korea grant 2009-0087452); Seoul Male Cancer Cohort (Seoul Male, funding sources: National R&D Program for Cancer Control, Ministry of Health & Welfare, Republic of Korea (0520160-1)); Singapore Chinese Health Study (SCHS, funding sources: NIH (R01CA55069, R35CA53890, R01CA80205, R01CA144034, UM1CA182876)); CardioVascular Disease risk FACtor Two-township Study (CVDFACTS, funding sources: Department of Health, Taiwan (DOH80-27, DOH81-021, DOH8202-1027, DOH83-TD-015 and DOH84-TD-006)); Mumbai Cohort Study (Mumbai, funding sources: International Agency for Research on Cancer, Clinical Trials Service Unit/Oxford University, World Health Organization) and Health Effects of Arsenic Longitudinal Study (HEALS, funding sources: NIH grants P42ES010349, R01CA102484 and R01CA107431). All Japanese cohorts—three Prefecture Cohort Study Aichi (3-Prefecture Aichi), Japan Public Health Center-based Prospective Study (JPHC1 and JPHC2), Three Prefecture Cohort Study Miyagi (3-Prefecture Miyagi), Miyagi Cohort Study (Miyagi) and Ohsaki National Health Insurance Cohort Study (Ohsaki)—are supported by the Grant-in-aid for Cancer Research, the Grant for the Third Term Comprehensive Control Research for Cancer, the Grant for Health Services, the Grant for Medical Services for Aged and Health Promotion, the Grant for Comprehensive Research on Cardiovascular and Lifestyle-Related Diseases from the Ministry of Health, Labour and Welfare, Japan and the Grant for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology, Japan. Japan Public Health Center-Based Prospective Study (JPHC1 and JPHC2) are also supported by the National Cancer Center Research and Development Fund. The corresponding author had full access to all the data and had final responsibility for the decision to submit for publication.
Disclaimer The funder of the study had no role in study design, data collection, data analysis, data interpretation or writing of the report.
Competing interests None declared.
Patient consent for publication Not required.
Ethics approval The current pooling project and individual cohort studies were approved by relevant Institutional Review Boards and ethics committees.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data are available on reasonable request. Data access can be through permission from the Asia Cohort Consortium only; please find more details on https://www.asiacohort.org/about/workingwith/index.html and send any inquiries to the Asia Cohort Consortium Coordinating Center at firstname.lastname@example.org.
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