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.

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.

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.

"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.

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The article has been published on doi: 10.3390/nu11040725