Comments on “Modulation of NRF2 and CYP24A1 Pathways by Hookah Smoke: Implications for Male Reproductive Health”

Dear Editor,

I read with great interest the Iranian study aiming to evaluate the effect of narghile smoking (NS) on sperm quality and the expression of nuclear factor erythroid 2-related factor 2 (NRF2) and Cytochrome P450 family 24 subfamily A member 1 (CYP24A1) genes (Firouzabadi et al., 2024). Firouzabadi et al. (2024) reported that NS has no statistically significant detrimental effects on sperm count, motility, or morphology, and highlighted that the increased expression of NRF2 in sperm suggests a potential adaptive response to oxidative stress (OS) caused by narghile smoke. Studies such as this are highly encouraged for several reasons. First, NS has been flourishing and regaining popularity worldwide (Pratiti & Mukherjee, 2019; WHO, 2015), thus becoming a worrying public health risk (Ben Saad, 2009, 2010; Bou Fakhreddine et al., 2014; Chaouachi, 2009a; El-Zaatari et al., 2015; Pratiti & Mukherjee, 2019; Waziry et al., 2017; WHO, 2015). In some countries, the prevalence of NS has surpassed cigarette smoking in some subcategories (WHO, 2015). Second, public opinion often misapprehends the damaging effects of NS (Pratiti & Mukherjee, 2019; WHO, 2015). Many individuals mistakenly consider it “safer” than cigarette smoking (Pratiti & Mukherjee, 2019; WHO, 2015), despite its association with numerous adverse health effects (Ben Saad, 2010; Bou Fakhreddine et al., 2014; El-Zaatari et al., 2015; Waziry et al., 2017). Results highlighting the impact of NS should be emphasized (Ben Saad, 2009, 2010; Chaieb & Ben Saad, 2021) because ignoring its serious implications for fertility could lead to public health challenges that physicians will need to address (Chaieb & Ben Saad, 2021; WHO, 2015). Third, NS has been linked to OS (Tofighi Niaki et al., 2023), a key factor in male infertility (Inhorn & Buss, 1994). Sperm are highly sensitive to oxidative damage due to their narrow antioxidant defenses (Tofighi Niaki et al., 2023). By studying the effects of NS on sperm quality, researchers can better understand its role in reducing male fertility. Fourth, NRF2 is a critical regulator of the cellular antioxidant response, and CYP24A1 is involved in vitamin D metabolism, which also affects OS and cell signaling (Shilovsky & Ashapkin, 2022). Evaluating the expression of these genes can help elucidate how NS disrupts the ability of the body to counteract OS at the molecular level, providing insights into potential mechanisms and therapeutic targets for mitigating its harmful effects. Finally, the 2015 World Health Organization advisory note on NS (WHO, 2015) called for additional research into NS-associated disease risks. In summary, evaluating the effects of NS on sperm quality and the expression of NRF2 and CYP24A1 genes is essential for understanding the mechanisms through which NS may compromise male reproductive health via OS and impaired antioxidant defense pathways. However, several methodological clarifications in the study by Firouzabadi et al. (2024) are needed.

The first point concerns one ambiguous exclusion criterion. Firouzabadi et al. (2024) excluded participants with a history of heavy cigarette smoking but did not clearly specify whether exclusive narghile smokers were considered. This lack of clarity may have led to the inclusion of both narghile smokers and light cigarette smokers, introducing confounding variables that could affect the conclusions of the study about the specific impacts of NS on sperm quality and gene expression (Chaouachi, 2006). Including ex-light cigarette smokers who transitioned to NS is a methodological error (Chaouachi, 2006) because the body retains a behavioral and physiological memorial of earlier smoking practices (Chaouachi, 2009a). Future studies should explicitly include only exclusive narghile smokers to eliminate this ambiguity.

The second point is the absence of a sample size determination, which is a statistical flaw (Serhier et al., 2020). Determining the optimal sample size is crucial in clinical research, as it ensures adequate power to detect statistical effects (Mascha & Vetter, 2018) and provides a representative sample for detecting significance (Serhier et al., 2020). While large sample sizes can be costly and expose more participants to procedures (Mascha & Vetter, 2018), insufficient participant numbers reduce the precision of results.

The third point pertains to the non-reporting of effect sizes in the comparative analysis by Firouzabadi et al. (2024). Although data from a control group (n = 52) and a narghile smoker group (n = 32) were compared, Firouzabadi et al. (2024) did not report effect sizes for these comparisons. Effect sizes provide a quantitative measure of the strength and magnitude of observed associations, offering a more nuanced understanding of practical significance (Olejnik & Algina, 2000). Reliance solely on p-values, as seen in the Iranian study (Firouzabadi et al., 2024), limits the interpretability of findings. Reporting effect sizes, such as Cohen’s d, would elucidate the clinical relevance of the observed differences (Olejnik & Algina, 2000). For example, in the study by Firouzabadi et al. (2024), the effect size for one primary metric (e.g., mean ± standard error of the mean of sperm normal morphology [%]: 4.67 ± 0.89 vs. 4.08 ± 1.21 for the control and narghile smoker groups, respectively) is large (Cohen’s d = −0.577).

The fourth point relates to the use of the word “hookah” to describe the smoking technique involving smoke passage through water before inhalation (Ben Saad, 2015; Khemiss et al., 2015). Terminology for this smoking practice varies by region and includes terms such as arghil, arghila, arghileh, argil, argileh, Borry, chicha, Chichi, chilam, ghelyan, goza, gozha, guza, hooka, hookah, hubbl bubbl, hubble bubble, hubble-bubble, hukka, huqqa, narghil, narghile, nargil, narguile, narguilé, narguileh, narguilhe’, sheesha, shisha, water pipe, waterpipe, and water-pipe (Ben Saad, 2015; Chaieb & Ben Saad, 2021). Grouping distinct methods under a universal term (e.g., hookah) constitutes methodological oversimplification (Ben Saad, 2009, 2015; Khemiss et al., 2015). This scientific reductionism and nominalism have fueled global confusion (Ben Saad, 2009, 2010; Khemiss et al., 2015). Examples of such confusion have been documented by an international expert (Chaouachi, 2009b; Chaouachi, 2007).

The fifth point concerns the lack of information about the brands of narghile tobacco used (Ben Saad, 2015). Narghile tobacco comes in three distinct brands: Tombak (often smoked in Asia) with direct contact with charcoal), Jurak (often smoked in Africa), and Tabamel or Moassel (a combination of Tombak and Jurak) with no direct contact with charcoal (Ben Saad, 2009; Chaouachi, 2006, 2015). Effects on fertility may differ depending on the tobacco brand (Ben Saad, 2009, 2010; Chaouachi, 2009a). Future studies should specify the brand of narghile tobacco smoked to facilitate comparisons between studies.

To conclude, evaluating the effects of NS on fertility has clinically significant implications. Future studies should be conducted and reported with greater methodological rigor, addressing the factors discussed above. This letter to editor serves as a call to encourage further research to determine the true implications of NS for male reproductive health.