Smoking and lung cancer paradox in Kerala: An Epidemiological Epiphany

In this blog post Professors Kesavan Rajasekharan Nayar and Raghu Ram K. Nair highlight the emerging smoking-lung cancer paradox in Kerala and posit some tentative explanations. The BMJ played a historical role in establishing the relationship between smoking and lung cancer way back in the 1950s by publishing classic studies by Doll and Hill and other scholars.  It appears that the epidemiological uncertainty regarding the relationship between smoking and lung cancer would continue for some more time.

The uncertainty now emerges from the state of Kerala in India where available data shows that men in Kerala smoke less, probably due to campaigns and strict punitive measures. The rate of smoking, at least in open spaces, has dropped sharply. Among adolescents, the rate is very low compared to other Indian states.¹ The Global Audit Tobacco Survey has found that tobacco use has come down to 12.7% in 2016–17 from 21.4% in 2009–10. Smoking habits have dropped to 9.3% from 13.4% during the same period. However, the incidence of lung cancer is one of the highest in India. In fact, lung cancer still occupies the top position among the leading types of cancers seen in men in Kerala. The hospital-based Cancer Registries in Thalassery, Kochi, and Thiruvananthapuram, and the Population–based Registry at Kollam in Kerala reported the incidence of lung cancer in men during 2012–2014 as 26.2%, 12.1%, 13% and 18.2%respectively, while the world average is 14.5%, and the Indian average is only 6.9 %.^{2, 3, 4}

This is a different type of smoking paradox compared to the Japanese paradox where men in that country smoke more than men in the United States but still have a lower lung cancer rate. There are several explanations for this paradox, such as age at initiation, use of filters, genetic factors, etc.⁵

The Kerala paradox needs an explanation in order to develop effective public health programmes to counter it. One of the general explanations is that it will take time to bring down the rates of lung cancer due to the long-lasting impacts of smoking. Lung cancer usually manifests in the fifth or sixth decade of life. So a reduction of this habit seen in the young population today may have to wait for a few more years for its effect to be appreciated. But it is also necessary to examine other issues such as prevalence of TB in Kerala, which could be under-reported. One of the salient explanations could be climatic change, which is widely perceived as a contributing factor for the rising incidence of non-communicable diseases in Kerala. Increasing rates of lung cancer seen among non-smokers, including women, could be due to such factors. Issues such as climate change, rising air pollution due to vehicular emissions, widespread practice of burning wastes, especially plastics, indiscriminate dumping of biodegradable and non-biodegradable wastes all over Kerala and extensive construction activities do need an empirical-epidemiological lens in this so-called healthy state in India. The role of supporting factors such as extremely high intake of alcohol, consumption of vegetables and fruits laden with highly toxic pesticides and dietary changes also need to be understood.

Professor Kesavan Rajasekharan Nayar MA., MCH, PhD

Global Institute of Public Health and Santhigiri Research Foundation, Thiruvananthapuram

Professor Raghu Ram K. Nair Ph.D

Formerly Professor & Head, Radiation Physics Division, Regional Cancer Centre, Thiruvananthapuram

References.

1. Jaisoorya TS, Beena KV, Beena M, et al. Prevalence and correlates of tobacco use among adolescents in Kerala, India. Indian J Med Res. 2016 Nov; 144(5): 704–711.
2. Amma JP, Sebastian PJ. Burden of cancers: Registry based data from Kerala, India. Health Systems. March 2017. Accessed http://jhs.healthequity.co.in/2017/03.
3. National Cancer Registry Program: Three year report of Population Based Cancer Registries 2012-2014. Report of 27 PBCRs. 2016. Bangalore: NCDIR-NCRP.
4. Bray F, Ferlay J, Soerjomataram I, Siegel RL, et al. Global cancer statistics 2018: GLOBOCAN estimates of incidence and mortality worldwide for 36 cancers in 185 countries. CA Cancer J for Clinicians 2018; 68 (6): 394-424.
5. Keum Ji Jung KJ, Christina J, Jee SH. The effect of smoking on lung cancer: ethnic differences and the smoking paradox. Epidemiology and Health 2016; 38: e2016060.