1. Introduction

It has been estimated that around 7 million of global deaths per year were caused by smoking [1-3]. Reviews of published systematic reviews and meta-analysis have confirmed that the risk of lung cancer and asthma has increased in current and former smokers [4-8]. In fact, tobacco smoke is the largest contributor to the most common histological types of lung cancer such as adenocarcinoma and small-cell and squamous cell carcinoma, with over 76% of lung cancer deaths in men and 37-42% of lung cancer deaths in women aged ≥50 years are attributable to tobacco use [9]. Tobacco smoke provokes asthma exacerbations and causes other allergy symptoms to worsen in adults. There is also unequivocal evidence that secondhand smoke exposure is the main contributor to asthma and lung cancer risk in nonsmokers, disproportionately affecting women [4]."People with asthma are generally at higher risk of lung cancer than the general population, whether they smoke or are exposed to tobacco smoke", Dr. Naser Alsharairi from Griffith University said.

It has been estimated that around 7 million of global deaths per year were caused by smoking ^[1][2][3]. Reviews of published systematic reviews and meta-analysis have confirmed that the risk of lung cancer and asthma has increased in current and former smokers ^{[4][5][6][7][8]}. In fact, tobacco smoke is the largest contributor to the most common histological types of lung cancer such as adenocarcinoma and small-cell and squamous cell carcinoma, with over 76% of lung cancer deaths in men and 37-42% of lung cancer deaths in women aged ≥50 years are attributable to tobacco use ^[9]. Tobacco smoke provokes asthma exacerbations and causes other allergy symptoms to worsen in adults. There is also unequivocal evidence that secondhand smoke exposure is the main contributor to asthma and lung cancer risk in nonsmokers, disproportionately affecting women ^[4]. The researcher claims that "people with asthma are generally at higher risk of lung cancer than the general population, whether they smoke or are exposed to tobacco smoke".

There is controversy over the role of dietary supplements in reducing or treating lung cancer in smokers and nonsmokers. There is also much uncertainty about its effectiveness and the consequences in asthmatic smokers and nonsmokers, and our understanding of whether dietary supplements can reduce lung cancer risk in asthmatic smokers and nonsmokers remains unclear in the absence of clinical trials. "In order to evaluate the safety and effectiveness of dietary supplement use by asthmatic smokers and nonsmokers before, during, and after lung cancer treatment, we need realistic and reliable studies worldwide", says Dr. Alsharairi.

There is controversy over the role of dietary supplements in reducing or treating lung cancer in smokers and nonsmokers. There is also much uncertainty about its effectiveness and the consequences in asthmatic smokers and nonsmokers, and our understanding of whether dietary supplements can reduce lung cancer risk in asthmatic smokers and nonsmokers remains unclear in the absence of clinical trials . The researcher claims that "in order to evaluate the safety and effectiveness of dietary supplement use by asthmatic smokers and nonsmokers before, during, and after lung cancer treatment, we need realistic and reliable studies worldwide".

Dr. Alsharairi conducted a comprehensive literature review on this topic, searching for prospective studies and randomised controlled trials (RCTs) on the effects of supplements and/or vitamin/mineral intake on asthma and lung cancer risk and total mortality rate, with the overall results stratified by smoking status or groups. He identified a total of 20 studies that focused on both lung cancer and asthma.

2. Data, Applications and Influences

"The results across studies have been contradictory regarding the effects of dietary supplements on lung cancer risk and mortality in smokers and nonsmokers. However, some studies urged caution in recommending long-term, high-dose supplements that contain β-carotene, retinyl palmitate, B vitamins and vitamin E for lung cancer patients, particularly current and former smokers", says Dr. Alsharairi. He also said "There is too little known about the effects of dietary supplements on asthma risk in smokers. Although vitamin D supplementation alone has proven beneficial in reducing asthma risk in current/former smokers, the intake of vitamin D supplements together with calcium/other supplements may not be advocated. We need more research to clarify the effects of dietary supplements on asthma risk in both smokers and nonsmokers". There is still a gap in knowledge with respect to the effects of dietary supplements on lung cancer risk/mortality in asthmatic smokers and nonsmokers. Dr. Alsharairi is therefore suggesting future trials and prospective studies of these supplements to detect their benefits and harms.

Dietary supplements use has increased globally ^[10], and have become of particular interest to consumer and the pharmaceutical companies ^[11][12], in addition to be significant part of complementary medicines to maintain or improve health ^[13][14]. The most common dietary supplements used by cancer and asthmatic patients were multivitamins and antioxidants ^[15][16][17].

1. Schane, R.E.; Ling, P.M.; Glantz, S.A. Health effects of light and intermittent smoking: A review. Circulation

2010, 121, 1518–1522.

2. West, R. Tobacco smoking: Health impact, prevalence, correlates and interventions. Psychol. Health. 2017, 32,

1018–1036.

3. GBD 2015 Tobacco Collaborators. Smoking prevalence and attributable disease burden in 195 countries and

territories, 1990–2015: A systematic analysis from the Global Burden of Disease Study 2015. Lancet 2017, 389,

1885–1906.

There is strong belief that taking dietary supplements prevents occurrence of cancers ^[18]. To the contrary, these supplements are not safe for cancer patients and have increased risk of mortality in Westernized adult populations ^[19]. Indeed, studies have been contradictory regarding the effects of dietary supplements on lung cancer risk and mortality in smokers and nonsmokers . However, there is now scientific evidence that urged caution in recommending long-term, high-dose supplements that contain β-carotene, retinyl palmitate, B vitamins and vitamin E for lung cancer patients, particularly current and former smokers ^[20].

4. Jayes, L.; Haslam, P.L.; Gratziou, C.G.; Powell, P.; Britton, J.; Vardavas, C.; Jimenez-Ruiz, C.; Leonardi-Bee, J.;

Tobacco Control Committee of the European Respiratory Society. SmokeHaz: Systematic reviews and

meta-analyses of the effects of smoking on respiratory health. Chest 2016, 150, 164–179.

Given that long-term supplements use can have adverse effects, why do companies still claim of anticancer benefits for marketing of these supplements? Pharmaceutical companies have not adequately complied with dietary supplement manufacturing standards. These supplements contain harmful ingredients which continue to be sold to cancer patients for economic reasons ^[21]. Sales of dietary supplements could represent harm, rather than health benefits, if national standards and regulations do not rigorously apply. Despite the efforts of the Western countries to improve supplements safety and quality in the marketplace, many challenges still exist. These include inadequate assurance of safety/efficacy, inaccuracy of product labeling, misleading health claims and lack of conceptual clarity concerning a regulatory framework for marketing and assessing the quality of supplements ^{[22][23][24][25]}.

5. Skaaby, T.; Taylor, A.E.; Jacobsen, R.K.; Paternoster, L.; Thuesen, B.H.; Ahluwalia, T.S.; Larsen, S.C.; Zhou, A.;

Wong, A.; Gabrielsen, M.E.; et al. Investigating the causal effect of smoking on hay fever and asthma:

A Mendelian randomization meta-analysis in the CARTA consortium. Sci. Rep. 2017, 7, 2224.

6. Santillan, A.A.; Camargo, C.A., Jr.; Colditz, G.A. A meta-analysis of asthma and risk of lung cancer

(United States). Cancer Causes Control 2003, 14, 327–334.

7. Rosenberger, A.; Bickeböller, H.; McCormack, V.; Brenner, D.R.; Duell, E.J.; Tjønneland, A.; Friis, S.;

Muscat, J.E.; Yang, P.; Wichmann, H.E.; et al. Asthma and lung cancer risk: A systematic investigation by the

International Lung Cancer Consortium. Carcinogenesis 2012, 33, 587–597.

8. Qu, Y.L.; Liu, J.; Zhang, L.X.; Wu, C.M.; Chu, A.J.; Wen, B.L.; Ma, C.; Yan, X.Y.; Zhang, X.; Wang, D.M.; et al.

Asthma and the risk of lung cancer: A meta-analysis. Oncotarget 2017, 8, 48525.

RCTs revealed that dietary supplements including methyl donor nutrients and antioxidant vitamins were found not to improve pulmonary function in patients with asthma ^[26]. Pharmaceutical companies are involved in manufacturing supplements purported for use in asthma such as Quercetin and Pycnogenol ^[27]. A need remains for more efforts to provide regulatory guidelines about using dietary supplements to reduce asthma risk. Few RCTs to date have sought to examine the effects of dietary supplements on asthma risk in smokers. Although vitamin D supplementation alone has proven beneficial in reducing asthma risk in current/former smokers, the intake of vitamin D supplements together with calcium/other supplements may not be advocated . Further RCTs to examine the efficacy of dietary supplements in improving asthma symptoms are needed ^[28]. More studies are also needed to clarify the effects of dietary supplements on asthma risk in both smokers and nonsmokers.

9. Institute for Health Metrics and Evaluation. Global Burden of Disease 2017. 2017. Available online:

http://vizhub.healthdata.org/gbd-compare/# (accessed on 24 December 2018).

3. Conclusion

Dietary supplements use in lung cancer prevention elicits considerable controversy. Long-term use of specific dietary supplements appears to increase lung cancer risk. The naturopathy sector makes millions of dollars by making claims about cancer-fighting supplements- this should be backed up with empirical research, and if it's false, those companies should not be profiting from misleading people. Dietary supplements might actually reduce other cancers risk because some studies have made very grand claims. Given active and passive smoking are the main risk factors for asthma and lung cancer, the researcher is therefore suggesting future trials and prospective studies of these supplements to detect their benefits and harms for lung cancer prevention in asthmatic smokers and non-smokers.

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The article has been published on doi: 10.3390/nu11040725