***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: The aim was to study whether  occasional smoking  increases mortality risk .  The mortality of r and om sample s of the Finnish Adult Health Behavior surveys from 1978 to 1991 were followed for 18 years from 1978 to 1995 . Poisson models were used to determine the risk of total and cardiovascular mortality . It was found that occasional smokers were less often sedentary and had less often unhealthy diet than other smoking status groups . Occasional smoking among men was significantly related to the risk of both total ( age-adjusted relative risk , RR , 1.6 , 95 % confidence interval , CI , 1.3 - 2.1 ) and cardiovascular mortality ( age-adjusted RR 1.5 , 95 % CI 1.0 - 2.3 ) . Controlling for education , period and chronic morbidity did not change results . Among women no significant associations could be established ; when adjusted for age , period , education and morbidity the RR for cardiovascular mortality was 1.4 ( 95 % CI 0.6 - 3.4 ) and total mortality 1.0 ( 95 % CI 0.6 - 1.6 ) . Occasional smoking is associated with increased risk of premature death , at least among men . Although occasional smoking is a less dangerous practice than regular smoking , it is not a safe alternative for daily smoking Objective : To determine the risk of dying from specified smoking-related diseases and from any cause in heavy smoking men and women ( ⩾15 cigarettes/day ) , who reduced their daily cigarette consumption by > 50 % . Design : A prospect i ve cohort study . Setting : Three counties in Norway . Participants : 24 959 men and 26 251 women , aged 20–49 years , screened for risk factors of cardiovascular disease in the mid-1970s , screened again after 3–13 years , and followed up throughout 2003 . Outcomes : Absolute mortality and relative risks adjusted for confounding variables , of dying from all causes , cardiovascular disease , ischaemic heart disease , all smoking-related cancer and lung cancer . Results : With sustained heavy smokers as reference , the smokers of both sexes who reduced their daily consumption ( reducers ) had the following adjusted relative risks ( 95 % confidence interval ( CI ) ) : of dying from any cause , 1.02 ( 0.84 to 1.22 ) ; cardiovascular disease , 1.02 ( 0.75 to 1.39 ) ; ischaemic heart disease , 0.96 ( 0.65 to 1.41 ) ; smoking-related cancer , 0.86 ( 0.57 to 1.29 ) ; and lung cancer , 0.66 ( 0.36 to 1.21 ) . The difference in cigarette consumption between two examinations was not a significant predictor of death from any of the causes . A follow-up from a third screening of the subgroup who were reducers at both second and third examinations ( sustained reducers ) did not have a lower risk than those who were heavy smokers at all three examinations . Conclusions : Long-term follow-up provides no evidence that heavy smokers who cut down their daily cigarette consumption by > 50 % reduce their risk of premature death significantly . In health education and patient counselling , it may give people false expectations to advise that reduction in consumption is associated with reduction in harm We previously reported that the metabolism of cotinine , the proximate metabolite of nicotine , is significantly slower in black than in white cigarette smokers . To underst and why the metabolism of nicotine and cotinine might differ between blacks and whites , we studied the pattern of nicotine metabolism in blacks and whites . One hundred eight healthy smokers ( 51 blacks and 57 whites ) , of similar age , gender distribution , and smoking history , received an i.v . infusion of deuterium-labeled nicotine and cotinine . The clearance of cotinine , the fractional conversion of nicotine to cotinine , and the metabolic clearance of nicotine to cotinine were significantly lower in blacks than in whites . Blacks excreted significantly less nicotine as nicotine-N-glucuronide and less cotinine as cotinine-N-glucuronide than whites , but there was no difference in the excretion of 3'-hydroxycotinine-O-glucuronide . Nicotine and cotinine glucuronidation appeared to be polymorphic , with evidence of slow and fast N-glucuronide formers among blacks but was unimodal with fast conjugators only among whites . Other findings of note included the demonstration of a significant correlation between the distribution volumes of nicotine and cotinine with lean body mass : there was a smaller distribution volume and a shorter half-life for cotinine in women than in men and a smaller volume of distribution of cotinine in blacks than in whites . We conclude that the metabolism of cotinine is slower in blacks than in whites because of both slower oxidative metabolism of nicotine to cotinine ( presumably via cytochrome P-450 2A6 ) and slower N-glucuronidation . Ethnic differences in the metabolism of other drugs undergoing N-glucuronidation should be studied To develop and compare methods that predict individual nicotine ( NIC ) clearance , which reflects CYP2A6 activity , using r and om saliva cotinine ( COT ) and trans 3′-hydroxycotinine ( 3HC ) measurements . COT and 3HC saliva concentrations in smokers were simulated utilizing a mechanistic population pharmacokinetic model of NIC metabolism that was adapted from the one described in a companion paper . Four methods to predict NIC clearance using the metabolites concentrations were compared . The precision bias , and the fraction of predictions that are made with an absolute error below 25 % were the performance measures evaluated . Four prediction methods were compared : ( M1 ) reference method , an intercept slope model of the metabolite concentration ratios ( [3HC]/[COT ] ) ( M2 ) an intercept slope model of the natural logarithm of the metabolite ratios ( M3 ) a spline of the logarithm of the metabolite ratios ( M4 ) Maximal Posteriori Bayesian estimate of NIC clearance conditioned on the model , COT and 3HC concentrations . In addition , the effect of smoking patterns on the concentrations of COT and 3HC was evaluated . The precision , accuracy , and the fraction of predictions with an absolute error below 25 % , were higher for methods M2–M4 compared to method M1 . However , the differences between M2 and M4 were small . Additionally , smoking pattern did not affect the metabolite concentration profiles . Predicting NIC clearance using an intercept slope model of the natural logarithm of the ratio of 3HC to COT appears to be a relatively simple method that is better than using the metabolite ratio directly . This method has a bias of approximately −10 % , precision of approximately 60 % . The fraction of estimates below an absolute error of 25 % is 43 % . These results support use of M2 to estimate CYP2A6 activity in smokers in the clinical setting Objective and rationale Heavy social drinkers often engage in occasional cigarette smoking , especially in the context of consuming large quantities of alcohol . The current study assessed alcohol ’s effects on smoking urge as a function of alcohol dose and time course in tobacco chippers with heavy social drinking patterns . Method The study assessed 39 chippers who underwent three separate evening sessions . Each subject received a placebo ( 1 % volume alcohol as a taste mask ) , a low alcohol dose ( two to three drinks equivalent ) , and a high alcohol dose ( four to five drinks equivalent ) in r and om order . No smoking was permitted during the sessions and the participants were abstinent from smoking for at least 3 h before arrival . Throughout the session , cigarette craving was assessed by the Brief Question naire of Smoking Urges and alcohol response was assessed by the Biphasic Alcohol Effects Scale ( BAES ) . Results The results showed that alcohol significantly increased cigarette craving in a dose-dependent manner ( p<0.001 ) . At the high alcohol dose , craving was heightened during the rising portion of the blood alcohol curve ( BAC ) . There was a strong relationship between BAC and craving for positive reinforcement and this relationship was partially mediated by BAES stimulation , but not sedation . Conclusions The findings show that alcohol directly increases smoking urge in chipper smokers . Tobacco chippers may crave cigarettes more during heavier than during lighter drinking bouts , and this effect appears to be driven by heightened stimulation levels rather than as a means to offset alcohol ’s sedative effects Objectives : To determine the risk in men and women smoking 1–4 cigarettes per day of dying from specified smoking related diseases and from any cause . Design : Prospect i ve study . Setting : Oslo city and three counties in Norway . Participants : 23 521 men and 19 201 women , aged 35–49 years , screened for cardiovascular disease risk factors in the mid 1970s and followed throughout 2002 . Outcomes : Absolute mortality and relative risks adjusted for confounding variables , of dying from ischaemic heart disease , all cancer , lung cancer , and from all causes . Results : Adjusted relative risk ( 95 % confidence interval ) in smokers of 1–4 cigarettes per day , with never smokers as reference , of dying from ischaemic heart disease was 2.74 ( 2.07 to 3.61 ) in men and 2.94 ( 1.75 to 4.95 ) in women . The corresponding figures for all cancer were 1.08 ( 0.78 to 1.49 ) and 1.14 ( 0.84 to 1.55 ) , for lung cancer 2.79 ( 0.94 to 8.28 ) and 5.03 ( 1.81 to 13.98 ) , and for any cause 1.57 ( 1.33 to 1.85 ) and 1.47 ( 1.19 to 1.82 ) . Conclusions : In both sexes , smoking 1–4 cigarettes per day was associated with a significantly higher risk of dying from ischaemic heart disease and from all causes , and from lung cancer in women . Smoking control policymakers and health educators should emphasise more strongly that light smokers also endanger their health OBJECTIVES This study examined the prevalence of  occasional smoking  in a population of working adults , compared the characteristics of occasional and daily smokers , and prospect ively examined the long-term smoking patterns of occasional smokers . METHODS At 32 Minnesota work sites , 5681 r and omly selected workers were surveyed at baseline ; 5248 of these were surveyed again 2 years later . A cross-sectional sample of 5817 workers was also surveyed at follow-up . RESULTS Occasional smokers constituted 18.3 % of all smokers in the baseline sample and 21.5 % of all smokers in the cross-sectional sample surveyed 2 years later . Baseline occasional smokers were significantly more likely than daily smokers to have quit at follow-up . Job monotony or repetitiveness was related to an increase to daily smoking at follow-up among baseline occasional smokers , and a change to a more restrictive workplace smoking policy was associated with quitting . CONCLUSIONS The results confirm that a substantial proportion of smokers are low-rate users and suggest that the proportion may be rising . Further research on this group is warranted Although most smokers are nicotine-dependent , recent studies suggest that some very light smokers ( “ chippers ” , who smoke fewer than five cigarettes per day ) may smoke for decades without developing dependence . It was considered that slowed nicotine elimination and /or reduced nicotine tolerance might underlie chippers ' ability to maintain smoking at such low levels . To evaluate this hypothesis , we studied the elimination kinetics and pharmacodynamics of nicotine in chippers and matched regular smokers .  Plasma nicotine levels and cardiovascular responses were observed for several hours after subjects were administered uniform doses of tobacco smoke . Chippers did show less chronic nicotine tolerance , but only on some response measures . Their rates of nicotine elimination equaled those of regular smokers . This finding , when coupled with other data about chippers ' smoking patterns and nicotine absorption , establish that chippers can not maintain substantial plasma nicotine levels between cigarettes , and thus suggest that attempts to maintain minimal trough levels of nicotine do not underlie chippers ' smoking The Question naire of Smoking Urges ( QSU ) was design ed to measure cravings elicited by abstinence from cigarette smoking . In the present study , the sensitivity of the QSU both to brief periods of abstinence and to exposure to smoking-related cues was investigated . A progressive ratio ( PR ) operant procedure was also employed , in which behaviour was maintained either by primary reinforcement ( puffs on a cigarette ) or by secondary reinforcement ( tokens exchanged later for puffs on a cigarette ) in separate experiments . Dependent smokers , who were not abstinent or who were abstinent for either 2 or 4 h , were tested in both a cue-rich and a no-cue environment . The results indicated that the QSU was sensitive both to brief periods of abstinence and to exposure to smoking-related cues , but the effect of smoking-related cues on QSU scores was maximal in non-abstinent smokers . In contrast , neither abstinence nor exposure to smoking-related cues significantly influenced the number of reinforcers earned , or the number of responses made , in either PR task . However , there was a significant interaction between gender and degree of abstinence on PR performance under primary reinforcement , and correlations between 
    Output:
    
Results LITS inhale smoke and have post-smoking blood nicotine concentrations that are broadly equivalent to those found in daily smokers .
However , LITS differ from daily smokers with regard to cigarette consumption and frequency of cigarette use , sociodemographic and socioeconomic characteristics , motives , personality traits , dependence , withdrawal and craving , response to smoking-related cues , quitting perception , past-smoking status , and initiation .
Conclusions In contrast to daily smokers , LITS show few or no signs of dependence as currently defined by DSM-IV criteria , appear to exercise more self-control , seem to be less impulsive , and their smoking experience is primarily associated with positive rather than negative reinforcement .