the size , shape , and tobacco used in the hookah device vary in different regions ( 2 ) .
hookah smoking has increased worldwide and there has been a revival of its use in general population , especially among young people ( 3 , 4 ) .
moreover , there is a common misconception about hookah smoking that it is safer than other tobacco products ( 6 ) . in some countries ( like iran )
such situation , as well as lack of productspecific interventions and policies have led to popular beliefs among youth and young adults that hookah smoking is neither addictive nor hazardous ( 5 , 7 ) .
studies have reported that hookah smoking has been associated with lung cancer and other respiratory diseases ( 8) , periodontal diseases , low birth weight ( 9 ) and some effects on cardiovascular system ( 7 , 10 , 11 ) .
several studies from different regions and countries , like eastern europe ( 12 ) , united states ( 13 ) , jordan ( 14 ) , and syria ( 15 ) indicate an increasing and alarming trend of hookah smoking among university students . it should be noted that although hookah has been used traditionally in middle eastern countries ( 1 ) , akl et al . in a systematic review
concluded that the prevalence of hookah smoking appears to be alarmingly high among school and university students not only in middle eastern regions , but also in western countries ( 16 ) .
it should be noted that due to pressure of heavy workload , and in other hand higher medical knowledge , the prevalence of any substance use in medical university students may be different from the general population or other students ( 17 ) . despite the importance of hookah smoking among university students ,
there is little information about it in this high - risk group ( 18 ) .
the aim of this study was to determine the status of hookah smoking and its correlates in the students of tehran university of medical sciences during 2012 - 2013 .
the present cross - sectional study was conducted from autumn 2012 until winter 2013 using a multistage sampling method .
students were chosen as follows ; in each college ( strata ) , a number of classes ( clusters ) - proportion to size - were randomly selected and all students of the selected classes were included in the study .
proportion of females in the iranian universities of medical sciences in iran is about twice of males and this ratio was considered in our sample for ensuring the representativeness .
the questionnaire was aimed at obtaining information on hookah and cigarette smoking , alcohol use , use of prescription - type drugs ( including medications that contain opioid components , methylphenidate and sedatives or tranquilizers ) , and illicit drug use ( including cannabis , opium and its residue , heroin , stimulants such as methamphetamine , ecstasy and cocaine ) , as well as demographic information . in addition , the questionnaire inquired about cigarette or hookah smoking , alcohol use , substance use and use of prescription - type drugs in the family members and close friends .
more details about items and validity of the questionnaire have been presented elsewhere ( 17 ) .
the last year use was considered as a basis for statistical analyses of hookah , cigarette and alcohol use . for illicit substances ,
prescription - type drug use was defined as the use of opioid drugs and sedatives ( tranquilizers ) at least 3 times a week for the last month or last year use of methylphenidate .
chi - square test and multiple binary logistic regression analysis ( backward method ) were used for univariate and multivariate analyses , respectively . a p value < 0.05 was considered as statistically significant .
students were informed about the voluntary nature of the participation in the study and their right to reject participation in the study or skip any questions .
the response rate was 90.5% in the present study ( 1992 out of the 2212 distributed questionnaires ) .
the mean age of the participants was 21.16  3.15 years ( range : 16 - 44 ) .
the majority of the sample were females ( 69.2% ) and 7.9% were married . among 1992
students , 26.6% , 17.8% and 8.9% had used hookah in the lifetime , last year and last month , respectively .
demographic and key characteristics of the sample , as well as the conditional distribution of hookah smoking at each level of the variables are also shown in table 2 . according to this table , all variables had a significant association with last year hookah smoking except age , marital status and prescription - type drug use in the family .
the results of these analyses showed that male gender ( or = 2.8 , 95% ci : 1.86 - 4.21 ) , cigarette smoking in the past year ( or = 5.6 , 95% ci : 3.21 - 9.83 ) , alcohol use in the past year ( or = 7.4 , 95% ci : 4.01 - 13.06 ) , cigarette or hookah smoking in the family members ( or = 1.7 , 95% ci : 1.13 - 2.51 ) , cigarette or hookah smoking among friends ( or = 4.4 , 95% ci : 2.69 - 7.33 ) , alcohol use among friends in the past year ( or = 1.9 , 95% ci : 1.20 - 3.14 ) , and illicit substance use among friends ( or = 2.2 , 95% ci : 1.22 - 4.05 ) were associated with hookah smoking . abbreviation : ci , confidence interval .
use of opioid medications or sedatives ( tranquilizers ) at least 3 times a week for the last month or last year use of methylphenidate .
variables entered on step 1 : gender , age , marital status , living place , cigarette smoking , alcohol use , illicit substance use , illicit substance use in family , illicit substance use in friends , prescription - type drug use in family and prescription - type drug use in friends , cigarette or hookah smoking in family , cigarette or hookah smoking in friends , alcohol use in family , alcohol use in friends and prescription - type drug use .
in the present study , the lifetime , last year and past 30 day prevalence of hookah smoking were determined to be 26.6% , 17.8% and 8.9% , respectively . the prevalence of hookah smoking in the present study is similar to other studies conducted among university students in iran ( 20 , 21 ) .
for example , the prevalence of lifetime and last year smoking of hookah were reported to be 30% and 20.7% , respectively , in one study ( 20 ) and in another study 28.7% of males and 11.5% of females reported current hookah smoking ( 21 ) .
in addition , the prevalence of hookah smoking among students of zanjan ( occasionally and regular use ) and tabriz ( last use ) universities , iran , were reported as 13% , 4.2% and 8.5% , respectively ( 22 , 23 ) .
for example , the lifetime and past-30- day prevalence of hookah smoking have been reported to be 61.1% and 42.7% , respectively for university students of jordan ( 14 ) .
also , in a study among medical and nonmedical university students in turkey , the total prevalence rate of hookah smoking was found to be 32.7% ( 24 ) . in eastern mediterranean countries
the prevalence of last year hookah smoking among university students has been reported as 25.7% in monitoring the future ( mtf ) study in us ( 26 ) . in north carolina
this rate have been reported as 40% ( life time prevalence ) and 17% ( last 30 day prevalence ) ( 27 ) . among students of a university in united states ,
the lifetime , last year and past 30 day prevalence rates of hookah smoking was reported as 40.5% , 30.6% and 9.5% , respectively ( 28 ) . in a british university prevalence of hookah smoking
was found to be 38% ( lifetime ) and 8% ( regularly smoking ) ( 29 ) .
the results of a review showed that the prevalence of last month hookah smoking range from 6% to 34% among middle eastern adolescents and from 5% to 17% among american adolescents ( 25 ) .
this high prevalence has been attributed to its social acceptance ( 30 , 31 ) .
in addition , another factor that influences the spread of hookah smoking is that it is perceived to be less lethal and addicting than cigarette smoking ( 5 , 6 ) . our findings
, like previous studies from iran and other countries ( 4 , 29 , 32 , 33 ) , showed that hookah smoking is more prevalent in men than in women .
the logistic regression models demonstrated that odds of hookah smoking are 2.8 for males compared to females .
it should be noted that this difference is much higher in the case of cigarette smoking , alcohol and other illegal drug use .
it highlights this fact that female students show higher tendency to hookah smoking than to other substances .
we found that students who had smoked cigarettes and those who had used alcohol in the last year were more likely to use hookah compared with nonsmokers . due to the cross - sectional nature of the study
, we were not able to identify the temporal sequence of hookah smoking and the use of other substances . however , considering co - occurrence is one of the most effective approaches in prevention of high - risk behaviours .
numerous studies have emphasized the co - occurrence of hookah smoking and other risky behaviours ( 34 - 36 ) .
several studies indicated that involvement in one risky behavior is related with engagement in other risky behaviours ( 37 , 38 )
. this may be especially important for the hookah and cigarette smoking ; because in both tobacco is used by means of smoking ( 39 ) .
our findings indicated that hookah smoking was strongly associated with cigarette or hookah smoking by friends .
one of the most important factors that can affect the spread of hookah smoking is peers influence ( 3 ) .
heinz et al . showed that participants who were hookah users , as compared to nonusers , had a greater number of friends who had tried and approved hookah use ( 35 ) .
in addition , several studies indicate that if substance use is common in majority of friends , these youths probably will be pushed to consumption ( 40 , 41 ) .
it is also found that alcohol use and illicit substance use in friends are associated with hookah use among students .
hookah smoking is often a social phenomenon that occurs between friends and predominantly in cafes and bars ( 2 , 5 ) .
ghafouri et al . in a study among students of health sciences , stated that hookah smoking was perceived as a social activity among friends ( 42 ) .
because of religious and legal prohibition of alcohol use in iran , there is no social drinking in cafes and bars .
in such a case , hookah smoking has considerable importance and acts as a mean of socialization for the youth . in the present study
, it was found that hookah smoking is higher in those students with hookah smoking in family .
some studies have emphasized on parents substance abuse and increased chance of illicit substance use in children ( 43 , 44 ) .
the result of a study among michigan adults found that having a father , mother , or sibling who smoke hookah at home is a significant risk factor for hookah smoking ( 45 ) .
due to the cross - sectional design of the study , causal inference of our results can not be identified .
furthermore , findings of the study are relied on self - report data and it was assumed that the students were honest in answering the questions . for future studies , longitudinal studies are required to determine and monitor the incidence rate of hookah use and its correlates among medical university students .
the results of this study indicate lifetime , last year and last month use of hookah smoking among students of tehran university of medical sciences .
our findings show a relatively low prevalence of hookah smoking among iranian students in comparison to other studies .
the findings of this study can be used for planning and evaluating interventions by considering co - occurrence of hookah smoking with other risky behaviours .
this study has some limitations . due to the cross - sectional design of the study , causal inference of our results
furthermore , findings of the study are relied on self - report data and it was assumed that the students were honest in answering the questions . for future studies , longitudinal studies are required to determine and monitor the incidence rate of hookah use and its correlates among medical university students .
the results of this study indicate lifetime , last year and last month use of hookah smoking among students of tehran university of medical sciences .
our findings show a relatively low prevalence of hookah smoking among iranian students in comparison to other studies .
the findings of this study can be used for planning and evaluating interventions by considering co - occurrence of hookah smoking with other risky behaviours .
 backgroundhookah smoking has increased worldwide , especially among young people.objectivesthe aim of the present study was to determine the prevalence of hookah use and related factors in a sample of iranian students of medical sciences.materials and methodsa cross - sectional study was conducted on 1992 randomly selected sample of students of tehran university of medical sciences during 2012 - 2013 . a multistage sampling method was used and anonymous structured questionnaires were distributed to the students of each selected class 
 . chi - square test , fisher 's exact test and multiple binary logistic regression analyses were performed and p < 0.05 was considered as a significance level.resultslifetime , last year and last month prevalence rates of hookah smoking were 26.6% ( 95% ci : 24.7 - 28.6 ) , 17.8% ( 95% ci : 16.1 - 19.5 ) and 8.9% ( 95% ci : 7.7 - 10.2 ) , respectively . 
 the results of logistic regression model showed that male gender [ odds ratio ( or ) = 2.8 , 95% ci : 1.86 - 4.21 ] , cigarette smoking in the past year ( or = 5.6 , 95% ci : 3.21 - 9.83 ) , alcohol use in the past year ( or = 7.4 , 95% ci : 4.01 - 13.06 ) , cigarette or hookah smoking in the family members ( or = 1.7 , 95% ci : 1.13 - 2.51 ) , cigarette or hookah smoking among friends ( or = 4.4 , 95% ci : 2.69 - 7.33 ) , alcohol use by friends in the past year ( or = 1.9 , 95% ci : 1.20 - 3.14 ) , and illicit substance use among friends ( or = 2.2 , 95% ci : 1.22 - 4.05 ) were associated with hookah smoking.conclusionsthe results of our study indicate a relatively high prevalence of hookah smoking among iranian students . 
 the findings emphasize the importance of planning preventive interventions by considering different high - risk behaviors simultaneously . 
1. Background
2. Objectives
3. Materials and Methods
4. Results
5. Discussion
5.1. Limitations
5.2. Conclusions