"In contrast to what is believed, hookah tobacco smoking is not a safe alternative to smoking other forms of tobacco," says lead study author Nada Kassem.
The study is published in Cancer Epidemiology, Biomarkers & Prevention, a journal of the American Association for Cancer Research.
According to the researchers - led by Nada Kassem, associate director at the Center for Behavioral Epidemiology and Community Health at San Diego State University in California - the World Health Organization (WHO) and the US National Toxicology Program have classified benzene as a Group 1 carcinogen.
WHO further report that benzene is carcinogenic to humans, recommending that there is no safe level of exposure. Hookah smoke, however, is a source of benzene exposure and is, therefore, a risk factor for leukemia.
The most popular kind of hookah tobacco is known as Moassel, which is sweetened and flavored tobacco that contains about 30% tobacco fermented with molasses and fruits mixed with glycerin and chemical flavors.
Kassem and her colleagues note that in the US in 2013, it was reported that 26.6% of male and 23.2% of female college students have used hookah at some point in time. Alarmingly, 8.1% of male and 6.6% of female middle and high school students have also used the substance.
Hookah tobacco smoking is not only linked to increased risks for leukemia, but also for lung and oral cancers, coronary heart disease and pulmonary disease.
Because hookah smoking is often practiced in social settings, the researchers examined uptake of benzene in both hookah smokers and non-smokers who attended hookah social events in "naturalistic settings" - where hookah tobacco alone was smoked.
Both smokers and non-smokers had increased SPMA uptake
The team analyzed levels of S-phenylmercapturic acid (SPMA) - which is a metabolite of benzene - in the urine of 105 hookah smokers and 103 non-smokers. The urine samples came from the morning of and the morning after study participants attended a hookah smoking event at either a lounge or a private home.
Results showed that for smokers, uptake of SPMA increased 4.2-fold after smoking hookah tobacco at a hookah lounge and 1.9-fold after smoking in a private home. Meanwhile, non-smokers' uptake of SPMA increased 2.6-fold after attending an event at a hookah lounge.
Interestingly, non-smokers had similar levels of SPMA before and after attending a hookah event at a private residence. Kassem notes, however, that pre-house event benzene levels in non-smokers were as high as those found in post-hookah lounge event non-smokers - suggesting chronic benzene exposure in the former group.
"Hookah tobacco smoking involves the use of burning charcoal that is needed to heat the hookah tobacco to generate the smoke that the smoker inhales," explains Kassem, adding:
"In addition to inhaling toxicants and carcinogens found in the hookah tobacco smoke, hookah smokers and non-smokers who socialize with hookah smokers also inhale large quantities of charcoal combustion-generated toxic and carcinogenic emissions."
Hookah smoking 'not a safe alternative'
Another finding from their sample of participants revealed that hookah smokers were younger than non-smokers, had more close friends who were current hookah smokers, were more likely to allow hookah smoking in their homes and were more likely to live with at least one hookah smoker.
Kassem says that since "there is no safe level of exposure to benzene, our results call for interventions to reduce or prevent hookah tobacco use, regulatory actions to limit hookah-related exposure to toxicants including benzene, and include hookah smoking in clean indoor air legislation."
The researchers also note that health care professionals should raise public awareness that hookah tobacco smoke is a source of benzene exposure, a known risk factor for leukemia.
"In contrast to what is believed," says Kassem, "hookah tobacco smoking is not a safe alternative to smoking other forms of tobacco."
Medical News Today recently reported on a study that suggested cigar smoking is just as harmful as cigarette smoking.