Current prevalence pattern of tobacco smoking in Nigeria: a systematic review and meta-analysis

Smoking is a leading cause of preventable deaths and morbidity, linked to high burden of lung cancer, chronic obstructive pulmonary disease (COPD), ischemic heart diseases and stroke [1‐3]. It accounts for more than 7 million deaths annually with about 10% of these resulting from second-hand smoke [2]. There are around 1.1 billion smokers worldwide and about 80% of these live in low- and middle-income countries (LMICs), where more than two-thirds of smoking-related deaths occur [2].

Though global current smoking rates among adults decreased from 23.5 to 20.7% between 2007 and 2015 [4], this reduction was largely due to the declining smoking rates in Northern and Western Europe, North America and the Western Pacific regions [3, 4], where considerable measures have been implemented to tackle tobacco smoking. Conversely, smoking rate appears to be increasing in the Middle East and Africa [4]. For example, in sub-Saharan Africa, the consumption of tobacco increased by 57% between 1990 and 2009 [5]. A recent analysis of the Demographic Health Survey data of 30 sub-Saharan African countries revealed higher smoking rates, with prevalence as high as 37.7% among men in Sierra Leone [6].

Nigeria is the most populous country in Africa and has one of the leading tobacco markets in Africa, with over 18 billion cigarettes sold annually costing Nigerians over US$ 931 million [7, 8]. Following the 2003 World Health Organization (WHO) Framework Convention on Tobacco Control (FCTC) [2], Nigeria ratified the convention agreement in 2005, and in 2015 signed into law the National Tobacco Control (NTC) Act that regulates all aspects of tobacco control including advertising, packaging, and smoke-free areas [2]. Despite these initiatives, some reports suggest the prevalence of smoking in the country is rising at about 4% per year [8].

The WHO estimated about 13 million smokers in Nigeria in 2012 [7], with over 16,000 deaths attributable to smoking [9]. Increased commerce by international tobacco companies and the relative role they play in economic growth may have contributed to a rise in smoking rates [8, 10]. Although, some national estimates of smoking prevalence have been reported [11, 12], the exact number of smokers remains debated, which possibly hinders health policy. Concerns over current estimates include varying case definitions, representativeness of study samples or data, and poor study designs. We therefore conducted a comprehensive systematic search of the literature and synthesized data based on standard case definitions to estimate national and sub-national prevalence of smoking in Nigeria.

This is a review of publicly available studies and conducted as part of series on the epidemiology of non-communicable diseases (NCDs) in Nigeria. Methods have been described in detail in previous studies [13‐16]. No ethical approval was required. Study was conducted in line with the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines [17].

This study integrated smoking information from 64 moderate to high-quality studies to estimate the current prevalence of smoking in Nigeria. Although the prevalence of ever smokers increased between 1995 and 2015, we observed a decreasing prevalence of current smokers over the same period. This trend is in contrast to estimates reported, albeit based on limited data, in some countries insub-Saharan Africa, who have experienced rising smoking rates due to changing socio-economic status, rural-urban migration and increased cigarette affordability [91]. The decreasing smoking rates in Nigeria possibly reflect increased health risk awareness and better overall measures to help smokers quit in the country. For example, in a national survey, Kale and colleagues [92] reported that in the 12 months preceding their study, almost half of current smokers attempted to quit smoking, with over two-thirds of these receiving advice from care providers and counselors.

Despite the declining rates, we estimated about 11 million current smokers (10.6%) and 20 million ever smokers (19.2%) in 2015, which are still unacceptably high from an absolute perspective. In a nation-wide survey in 2012 [11], the prevalence of current smokers was 4% among adults Nigerians. This is much lower than estimated in this study, presumably due to challenges with sampling and case ascertainment. In a recent scoping exercise, Adeoye et al. [93] estimated a prevalence of current smokers at 19.7%. However, this estimate was not age-standardized, and a lower prevalence of ever smokers reported raises concerns on the quality of data. However, in 2015, the WHO reported a current smoking prevalence of about 9% among persons aged 15 years or more (17% among men and 1% among women) in Nigeria [7]. The overall prevalence and sex distribution are almost as reported in the current study. The higher smoking prevalence among men in Nigeria is well-documented [10, 93]. This perhaps represents a sustained pattern of smoking epidemic, and presents a valuable opportunity for developing effective policies and interventions learning from actions in developing countries [94, 95].

The median age at initiation of smoking in this study (16.8 years) is relatively low, reflective of a growing burden among adolescents and youths. Kale and colleagues [92] in their nation-wide survey noted that about two-thirds of the population started smoking before attaining 20 years. Adeoye et al. [93] reported lower age at initiation of 14.7 years in the country. Many have advocated for stiffer anti-tobacco laws in the country, particularly to address a growing use of tobacco products among youths [11].

The prevalence of smokers was notably higher in North-east Nigeria which may be expected given an ongoing armed conflict lasting more than a decade. Although the evidence of the association between smoking and conflict is limited and inconclusive [96], varying social situations among vulnerable populations are known to precipitate substance use [97]. With several persons displaced, children and adolescents out of school, and youths without jobs, substance use, including tobacco products, is likely to increase in these settings. Although Kale and colleagues [92] reported South-easterners as the highest consumers of tobacco products in the country, the deviance from our estimates suggests a need for more research to understand regional variations.

Although the NTC Act was signed into law in 2015 and the country has committed to the WHO FCTC since 2005 [18], Nigeria is not yet on track to achieve tobacco control targets [98]. For example, our estimates show that rural dwellers smoke almost at the same rate as urban dwellers, indicating that smoking, believed to be associated with urbanization, has gradually penetrated remote areas. Further, we estimated that current smokers consume an average of 10 cigarettes per person per day accounting for about 110 million cigarettes per day and over 40 billion cigarettes in 2015 alone. Vellios et al. [99] noted that the demand for cigarettes increased by 44% across many African countries between 1990 and 2012, with this leading to over 100% increase in cigarettes production over the same period in these countries. A thriving tobacco market raises serious public health concerns, particularly for a country with a relatively weak health system. Tobacco companies see these countries as emerging markets due to weak tobacco control regulations and several vulnerable populations [91, 94]. Careful incorporation of the WHO MPOWER package (targeted at reversing tobacco epidemic) [18] beyond the national level to state and local levels may complement successful measures like smoke-free legislation, taxes, health education and media campaigns [2, 7]. Besides, Nigeria needs to develop comprehensive surveillance systems to monitor the production, sales, and consumption of cigarettes to effectively achieve control targets [99].

The strength of this review lies in the number of studies retained (64) and population covered (54755), which spread across all geopolitical zones in the country. Herein, we have perhaps addressed an issue bordering on representativeness, which appears to be a leading concern in the understanding of the epidemiology of smoking in Nigeria [10]. We acknowledge that pooling prevalence rates from a range of studies conducted over a 27-year period (1990–2017) could affect reliability of our overall estimates; however, this was mainly done to understand the trend in smoking rates over this period, which our model and age-adjusted estimates clearly reflect (Table 3). Nonetheless, our estimates should be considered with the high heterogeneity reported. This perhaps could be due to diverse population characteristics, particularly those contributed by specific population groups. Our sensitivity analysis may have addressed this (ie. comparing general to specific populations), as excluding some of specific populations with higher prevalence of smoking could imply missing some necessary information on the use of tobacco and related products in the country. Varying study designs are also important sources of heterogeneity. Due to data limitations, we could not investigate other sources of heterogeneity, including socio-economic status, wealth index, employment status and religion. Finally, there were only two studies from the North-east, this should guide interpretation of the high estimates in the region.

While the prevalence of current smokers may be declining in Nigeria, the absolute number of active smokers remain one of the highest in Africa. Economic growth, improved socio-economic status, rapid migration, and increased cigarette affordability are key factors. As rural dwellers are almost as affected as urban dwellers, careful consideration is required during programming. Comprehensive measures and strict anti-tobacco laws targeting tobacco production and marketing need to be enforced across country levels.