***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: Objective : To analyse the effects of smoking reduction and smoking cessation on incidence of myocardial infa rct ion after adjustment for established cardiovascular risk factors . Design : Prospect i ve cohort study with record linkage to mortality and hospital registers . The association of individual change in smoking with myocardial infa rct ion was examined in Cox proportional hazard analyses with continuous heavy smokers ( ⩾5 cigarettes/day ) as reference . Setting : Pooled data from three population studies conducted in Copenhagen , Denmark . Participants : 10 956 men and 8467 women with complete information on smoking habits at two examinations five to ten years apart were followed up from the second examination for a first hospital admission or death from myocardial infa rct ion . Mean duration of follow up was 13.8 years . Main results : A total of 643 participants who were heavy smokers at baseline reduced their daily tobacco consumption by at least 50 % without quitting between first and second examination , and 1379 participants stopped smoking . During follow up 1658 men and 521 women experienced a fatal or non-fatal myocardial infa rct ion . After adjustment for cardiovascular risk factors , people who stopped smoking had a decreased risk of myocardial infa rct ion , hazard ratio 0.71 ( 95 % confidence intervals 0.59 to 0.85 ) . Smoking reduction was not associated with reduced risk of myocardial infa rct ion , hazard ratio 1.15 ( 95 % confidence intervals 0.94 to 1.40 ) . These associations remained unchanged after controlling for baseline illness in different ways . Conclusions : Smoking cessation in healthy people  reduces the risk of a subsequent myocardial infa rct ion , whereas this study provides no evidence of benefit from reduction in the amount smoked OBJECTIVES Cigarette smoking causes cardiovascular ( CV ) disease , but the relative roles of nicotine and other components of tobacco smoke remain unclear . We investigated the effect of stopping smoking by using nicotine replacement therapy ( NRT ) on hemorheology parameters , on the cotinine and thiocyanate plasma concentrations and the exhaled carbon monoxide ( CO ) . DESIGN Open , parallel-group trial ( intervention group and control smokers ) . SUBJECTS 197 males , aged 25 - 45 years , smoking > 20 cigarettes per day ( cpd ) . INTERVENTIONS 164 subjects were instructed to stop smoking and received NRT for 12 weeks and 33 acted as controls . After 12 weeks , NRT was discontinued and all subjects were followed-up at 26 weeks . Beginning with week 4 , the treated subjects were divided into abstainers ( self-reported , verified by exhaled CO < 10 ppm ) and nonabstainers , not able to stay abstinent since baseline . The group of the nonabstainers was stratified in 2 subgroups , the reducers ( smoked < 50 % of baseline number of cpd ) and relapsers ( smoked 50 - 100 % of baseline cpd ) . MAIN OUTCOME MEASURES Plasma viscosity , erythrocyte deformability , fibrinogen , transcutaneous partial oxygen tension ( tcpO2 ) , hematocrit , white blood cells , cotinine and thiocyanate plasma concentrations and exhaled CO , all assessed at 4 , 8 , 12 and 26 weeks . RESULTS After 6 months , plasma fibrinogen ( 228.2 vs. 275.4 mg/dl at baseline , p < 0.001 ) , tcpO2 ( 50.4 vs. 34.9 mm mercury at baseline , p < 0.0001 ) were significantly improved in abstainers , but changes in plasma viscosity and erythrocyte deformability were inconclusive . Cotinine and thiocyanate ( abstainers : 6.2 ng/ml at week 26 vs. 10.4 ng/ml at baseline , p < 0.0001 ) and expired CO ( abstainers : 30.4 vs. 4.2 ppm , control vs. week 26 , p < 0.0001 ) accurately followed the changes in smoking and /or NRT use in all of the groups . Other CV risk factors such as hematocrit and white blood cell count decreased to a greater extent in abstainers than in reducers and relapsers . Not only abstainers but also reducers did benefit of the temporarily stop smoking . CONCLUSIONS Smoking cessation improved CV parameters despite the measured cotinine and thiocyanate plasma levels , and use of nicotine medications did not negate these improvements . A smoking cessation for a short time and smoking of reduced cpd also improved these parameters temporarily BACKGROUND Smoking reduction has been introduced as an alternative to smokers unable or unwilling to quit but has never been implemented in a population -based intervention . METHODS Two thous and four hundred eight daily smokers in all motivational stages were included in a r and omised population -based intervention study , in Copenhagen , Denmark . Smokers , unwilling or unable to quit , were encouraged to reduce their tobacco consumption . Furthermore , smokers in the high-intensity intervention were offered participation in smoking reduction groups . RESULTS Twenty-three percent of those who attended both baseline and 1 year visit reported reduction by at least 5 g and 8 % reported a halving or more . Halving of tobacco consumption was achieved significantly more often than in the background population , OR = 2.6 ( 1.6 - 4.4 ) , even when assuming that non- participants had not reduced , OR = 1.7 ( 1.0 - 2.8 ) . Reduction of at least 5 g doubled the probability of increased motivation to quit and a halving increased it more than four times . The reductions were not vali date d. Less than 2 % attended the smoking reduction groups . CONCLUSION The smoking reduction intervention was significant in self-reported reduction of tobacco consumption and subsequently increased motivation to quit . This may open new perspectives , with reduction as a first step towards cessation , a possible supplement to smoking cessation strategies This study was undertaken to determine 1 ) whether reducing tobacco exposure during pregnancy increases the birth weight of term infants and 2 ) the relative effects of early- and late-pregnancy exposure to tobacco on infant birth weight . Data were obtained from the Smoking Cessation in Pregnancy project , conducted in public clinics in three states ( Colorado , Maryl and , and Missouri ) between 1987 and 1991 .  Self-reported cigarette use and urine cotinine concentration were collected from 1,583 pregnant smokers at study enrollment and in the third trimester . General linear models were used to generate mean adjusted birth weights for women who reduced their tobacco exposure by 50 percent or more and for those who did not change their exposure . Regression smoothing techniques were used to characterize the relation between birth weight and early exposure and birth weight and third-trimester exposure . Reducing cigarette use was associated with an increase in mean adjusted birth weight of only 32 g , which was not significant ( p = 0.33 ) . As third-trimester cigarette use increased , birth weight declined sharply but leveled off at more than eight cigarettes per day . Findings were similar when urine cotinine concentration was used . Women who smoke during pregnancy may need to reduce to low levels of exposure ( less than eight cigarettes per day ) to improve infant birth weight BACKGROUND Limited data are available on carcinogen uptake in smokers who reduce their smoking . To determine whether reducing the number of cigarettes smoked per day would lead to a corresponding reduction in carcinogen uptake , we measured levels of metabolites of the tobacco-specific lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone ( NNK ) in the urine of smokers who reduced their smoking for up to 26 weeks . METHODS We recruited 153 smokers , of whom 151 were r and omly assigned to a reduction group or a waitlist group .  In the reduction group of 102 smokers , we measured the metabolites 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol ( NNAL ) and its glucuronides ( NNAL-Gluc ) at two baseline times and at weeks 4 , 6 , 8 , 12 , and 26 after baseline . Smokers were then expected to reduce their number of cigarettes per day by 25 % in weeks 0 - 2 , 50 % in weeks 2 - 4 , and 75 % in weeks 4 - 6 and to maintain the reduced level through week 26 . In the waitlist group of 49 smokers , four baseline measurements over 7 weeks were made to assess the longitudinal stability of the metabolite measurements , and then the smokers began the reduction program . All statistical tests were two-sided . RESULTS For waitlist and reduction groups results were comparable . Statistically significant reductions in the lung carcinogen metabolites were observed at most intervals as smokers reduced the number of cigarettes smoked each day . However , the observed decreases were generally modest , always proportionally less than the reductions in cigarettes smoked per day , and sometimes transient . For example , among the 65 individuals in the reduction group who reduced cigarettes per day by 40 % or more during weeks 4 - 12 after baseline , mean decreases in cigarettes per day were 53 % ( week 4 ) , 74 % ( week 6 ) , 75 % ( week 8) , and 74 % ( week 12 ) ; whereas the corresponding mean reductions in NNAL plus NNAL-Gluc were 29 % , 33 % , 37 % , and 29 % . ( P<.001 for all NNAL plus NNAL-Gluc values ) CONCLUSIONS Statistically significant reductions in levels of urinary metabolites of a tobacco-specific lung carcinogen were achieved by reduction in smoking , but for most smokers , reductions were modest and transient STUDY OBJECTIVES To assess the effect of continued smoking and smoking reduction on cardiovascular biomarkers ( eg , WBC count , cholesterol concentrations , BP , heart rate ) . DESIGN , SETTING , AND PARTICIPANTS This study , conducted at the University of Minnesota , r and omized smokers interested in significantly reducing cigarette use but not quitting to either start 12 weeks of smoking reduction immediately ( n = 102 ) , assisted by nicotine replacement therapy  , or to a 6-week wait list ( n = 49 ) . Those starting smoking reduction were required to reduce smoking by 25 % for 2 weeks , 50 % for 2 weeks , and 75 % during the final 2 weeks . After 6 weeks , the subjects were asked to maintain a 50 % reduction or quit . Nicotine gum and , if necessary , nicotine patch were used to achieve reduction goals . The wait list group ( n = 49 ) smoked ad libitum for 6 weeks and then reduced smoking as previously described . MEASUREMENTS AND RESULTS Cardiovascular biomarkers ( eg , WBC count , cholesterol concentrations , BP , heart rate ) were assessed at several time points after enrollment . During ad libitum smoking , cardiovascular biomarkers remained relatively stable with correlation coefficients across the various time measurements , ranging from 0.44 to 1.00 ( p < 0.01 for all measures ) . Among successful nonabstinent reducers ( 64 of 151 subjects ) , significant improvements were found in many biomarkers ( eg , hemoglobin , hematocrit , RBC and WBC counts , lipids , BP , heart rate , respiratory symptoms , all p < 0.0167 ) . CONCLUSIONS These results show the availability of reliable and dose-sensitive biomarkers and that reduction in smoking can lead to significant but only modest changes in cardiovascular risk factors in healthy smokers . It is not known whether the reductions in cardiovascular risk factors observed after smoking reduction are also associated with reduced disease risk . Additional research is necessary to address this issue OBJECTIVE To evaluate the impact of cotinine-confirmed smoking reduction during pregnancy on infant birth weight and gestational age at birth . DESIGN Group analyses from a prospect i ve , r and omized smoking-cessation intervention trial using cotinine levels to assess smoking cessation and reduction . SETTING Four maternity clinics of Jefferson County Health Department in Birmingham , Ala. PATIENTS A total of 803 pregnant smokers and 474 never smokers with a fetal gestational age of 32 weeks or less at the first prenatal visit to a clinic . MAIN OUTCOME MEASURES Infant birth weight and gestational age at birth . RESULTS Infants who were born to women who quit smoking ( quitters ) had the highest mean birth weight ( 3371 + /- 581 g ) , followed by infants who were born to women who did not change smoking behavior ( no changers ) ( 3043 + /- 587 g ) . The mean infant birth weight of infants born to the quitters , adjusted by mother 's age , race , height , weight at baseline , and gestational age at delivery was 241 g heavier than that among the no changers ( P = .0008 ) and 167 g heavier than the reducers ( P = .04 ) . The adjusted mean infant birth weight of infants born to the reducers was 92 g heavier than that among the no changers ( P = .08 ) . White reducers with baseline cotinine levels greater than 100 ng/mL had 
    Output:
    
The limited data suggest that a substantial reduction in smoking improves several cardiovascular risk factors and respiratory symptoms .
In addition , smoking reduction is associated with a 25 % decline in biomarkers and incidence of lung cancer and a small , mostly nonsignificant , increase in birth weight .
There seem to be no substantial beneficial effects on lung function .
The evidence on other health effects and mortality is too limited to draw conclusions .