Maintain levels of nicotine but reduce other smoke constituents: a formula for "less-hazardous" cigarettes?

Interventions to reduce harm from continued tobacco use

BACKGROUND

Although smoking cessation is currently the only guaranteed way to reduce the harm caused by tobacco smoking, a reasonable secondary tobacco control approach may be to try and reduce the harm from continued tobacco use amongst smokers unable or unwilling to quit. Possible approaches to reduce the exposure to toxins from smoking include reducing the amount of tobacco used, and using less toxic products, such as pharmaceutical, nicotine and potential reduced-exposure tobacco products (PREPs), as an alternative to cigarettes.

OBJECTIVES

To assess the effects of interventions intended to reduce the harm to health of continued tobacco use, we considered the following specific questions: do interventions intended to reduce harm have an effect on long-term health status?; do they lead to a reduction in the number of cigarettes smoked?; do they have an effect on smoking abstinence?; do they have an effect on biomarkers of tobacco exposure?; and do they have an effect on biomarkers of damage caused by tobacco?

SEARCH METHODS

We searched the Cochrane Tobacco Addiction Group Trials Register (CRS) on the 21st October 2015, using free-text and MeSH terms for harm reduction, smoking reduction and cigarette reduction.

SELECTION CRITERIA

Randomized or quasi-randomized controlled trials of interventions to reduce the amount smoked, or to reduce harm from smoking by means other than cessation. We include studies carried out in smokers with no immediate desire to quit all tobacco use. Primary outcomes were change in cigarette consumption, smoking cessation and any markers of damage or benefit to health, measured at least six months from the start of the intervention.

DATA COLLECTION AND ANALYSIS

We assessed study eligibility for inclusion using standard Cochrane methods. We pooled trials with similar interventions and outcomes (> 50% reduction in cigarettes a day (CPD) and long-term smoking abstinence), using fixed-effect models. Where it was not possible to meta-analyse data, we summarized findings narratively.

MAIN RESULTS

Twenty-four trials evaluated interventions to help those who smoke to cut down the amount smoked or to replace their regular cigarettes with PREPs, compared to placebo, brief intervention, or a comparison intervention. None of these trials directly tested whether harm reduction strategies reduced the harms to health caused by smoking. Most trials (14/24) tested nicotine replacement therapy (NRT) as an intervention to assist reduction. In a pooled analysis of eight trials, NRT significantly increased the likelihood of reducing CPD by at least 50% for people using nicotine gum or inhaler or a choice of product compared to placebo (risk ratio (RR) 1.75, 95% confidence interval (CI) 1.44 to 2.13; 3081 participants). Where average changes from baseline were compared for different measures, carbon monoxide (CO) and cotinine generally showed smaller reductions than CPD. Use of NRT versus placebo also significantly increased the likelihood of ultimately quitting smoking (RR 1.87, 95% CI 1.43 to 2.44; 8 trials, 3081 participants; quality of the evidence: low). Two trials comparing NRT and behavioural support to brief advice found a significant effect on reduction, but no significant effect on cessation. We found one trial investigating each of the following harm reduction intervention aids: bupropion, varenicline, electronic cigarettes, snus, plus another of nicotine patches to facilitate temporary abstinence. The evidence for all five intervention types was therefore imprecise, and it is unclear whether or not these aids increase the likelihood of smoking reduction or cessation. Two trials investigating two different types of behavioural advice and instructions on reducing CPD also provided imprecise evidence. Therefore, the evidence base for this comparison is inadequate to support the use of these types of behavioural advice to reduce smoking. Four studies of PREPs (cigarettes with reduced levels of tar, carbon and nicotine, and in one case delivered using an electronically-heated cigarette smoking system) showed some reduction in exposure to some toxicants, but it is unclear whether this would substantially alter the risk of harm. We judged the included studies to be generally at a low or unclear risk of bias; however, there were some ratings of high risk, due to a lack of blinding and the potential for detection bias. Using the GRADE system, we rated the overall quality of the evidence for our cessation outcomes as 'low' or 'very low', due to imprecision and indirectness. A 'low' grade means that further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate. A 'very low' grade means we are very uncertain about the estimate.

AUTHORS' CONCLUSIONS

People who do not wish to quit can be helped to cut down the number of cigarettes they smoke and to quit smoking in the long term, using NRT, despite original intentions not to do so. However, we rated the evidence contributing to the cessation outcome for NRT as 'low' by GRADE standards. There is a lack of evidence to support the use of other harm reduction aids to reduce the harm caused by continued tobacco smoking. This could simply be due to the lack of high-quality studies (our confidence in cessation outcomes for these aids is rated 'low' or 'very low' due to imprecision by GRADE standards), meaning that we may have missed a worthwhile effect, or due to a lack of effect on reduction or quit rates. It is therefore important that more high-quality RCTs are conducted, and that these also measure the long-term health effects of treatments.

Interventions to reduce harm from continued tobacco use

BACKGROUND

It may be reasonable to try to reduce the harm from continued smoking amongst smokers unable or unwilling to quit. Possible approaches to reduce the exposure to toxins from smoking include reducing the amount of tobacco used, and using less toxic products. The interventions evaluated in controlled trials have predominantly attempted to reduce the number of cigarettes smoked.

OBJECTIVES

To assess the effect of interventions intended to reduce the harm from smoking on the following: biomarkers of damage caused by tobacco, biomarkers of tobacco exposure, number of cigarettes smoked, quitting, and long-term health status.

SEARCH STRATEGY

We searched the Cochrane Tobacco Addiction Group Specialised Register using free text and MeSH terms for harm reduction, smoking reduction and cigarette reduction. The initial search was in March 2006, updated in March 2007.

SELECTION CRITERIA

Randomized or quasi-randomized controlled trials of interventions in tobacco users to reduce amount smoked, or to reduce harm from smoking by means other than cessation. Outcomes were change in cigarette consumption, markers of cigarette exposure and any markers of damage or benefit to health, measured at least six months from the start of the intervention.

DATA COLLECTION AND ANALYSIS

We pooled trials with similar interventions and outcomes using a fixed-effect model. Other studies were summarised narratively.

MAIN RESULTS

The 13 included trials all evaluated interventions to help smokers cut down the amount smoked. Self-reported reduction in cigarettes per day (CPD) was validated by reduction in carbon monoxide (CO) levels. Most trials tested nicotine replacement therapy (NRT) to assist reduction. No eligible studies evaluated the use of potentially reduced-exposure products. In a pooled analysis of eight trials, NRT significantly increased the odds of reducing CPD by 50% or more for people using nicotine gum or inhaler or a choice of product compared to placebo (n=3273, odds ratio [OR] 2.02, 95% confidence interval [CI] 1.55 to 2.62). Where average changes from baseline were compared for different measures, CO and cotinine consistently showed smaller reductions than CPD. Whilst the effect for NRT was significant, small numbers of people in either treatment or control group successfully sustained a reduction of 50% or more. Use of NRT also significantly increased the odds of quitting (OR 1.90, 95% CI 1.46 to 2.47). One trial of bupropion failed to detect an effect on reduction or cessation. Four trials of different types of advice and instructions on reducing CPD did not provide clear evidence.

AUTHORS' CONCLUSIONS

There is insufficient evidence about long-term benefit to give firm support the use of interventions intended to help smokers reduce but not quit tobacco use. Some people who do not wish to quit can be helped to cut down the number of cigarettes smoked and reduce their carbon monoxide levels by using nicotine gum or nicotine inhaler. Because the long-term health benefit of a reduction in smoking rate is unclear this application of NRT is more appropriately used as a precursor to quitting.

Carboxyhemoglobin and thiocyanate as biomarkers of exposure to carbon monoxide and hydrogen cyanide in tobacco smoke

The determination of biomarkers in human body fluids is a useful tool, which allows the quantitative assessment of the exposure to chemicals or complex mixtures of chemicals and of early biological effects as a result of the exposure. Biomarkers require validation before their successful application in human studies. This review describes some general purposes of human biomonitoring and biomarkers including the requirements for validation. Risk assessment and harm reduction of smoking and tobacco products, respectively, is a very suitable field for the application of biomarkers. A brief historical review shows that the application of biomarkers of exposure and effect in human smoking goes back more than 150 years. Two 'classical' biomarkers of exposure to tobacco, namely carboxyhemoglobin (COHb and its equivalent carbon monoxide in exhalate, COex) and thiocyanate (SCN) in body fluids are discussed in terms of sources of exposure, metabolism, disposition kinetics and influencing host factors. Data on COHb/COex and SCN in nonsmokers and smokers as well as the power to discriminate between smokers and nonsmokers are presented. Both biomarkers are significantly correlated with the daily cigarette consumption. Smoking machine-derived yields of the precursors carbon monoxide and hydrogen cyanide were not correlated with COHb/COex and SCN, respectively. It is concluded that, while COHb/COex is a useful biomarker for assessing the smoke inhalation, preferably in controlled studies, the application of SCN in body fluids as a biomarker for smoking is limited, mainly due to the abundance of other sources for SCN.

Smoking topography, brand switching, and nicotine delivery: results from an in vivo study

OBJECTIVE

Exposure to toxins in tobacco smoke is influenced by how a cigarette is smoked. Cigarettes have been designed to allow for a range of puffing behavior and to provide different, nonlinear tar and nicotine yields in response to different puffing profiles. However, puffing behavior and its influence upon risk-exposure has yet to be assessed outside the laboratory, in smokers' natural environment.

METHOD

Fifty-nine adult smokers used a portable device to measure smoking topography over the course of three 1-week trials. Participants were asked to smoke their usual "regular yield" brand through the device for trial 1 and again, 6 weeks later, at trial 2. Half the subjects were then randomly assigned to switch to a "low-yield" brand for trial 3.

RESULTS

The findings show a high degree of stability in puffing behavior within the same subject over time but considerable variability between smokers. Smokers who were switched to a "low-yield" cigarette increased their total smoke intake per cigarette by 40% (P = 0.007), with no significant change in their salivary cotinine levels. Cigarettes smoked per day and nicotine yield were only weakly associated with salivary cotinine levels; however, salivary cotinine was strongly associated with a composite measure that included cigarettes per day, brand elasticity, and puffing behavior (sr = 0.61, P < 0.001).

CONCLUSIONS

These findings provide strong evidence of behavioral compensation to low-yield cigarettes from in vivo measures of smoking behavior. The findings also show the importance of brand elasticity and smoking topography in predicting nicotine uptake and smoke exposure.

Estimates of maximum or average cigarette tar, nicotine, and carbon monoxide yields can be obtained from yields under standard conditions

Average yields of tar, nicotine, and carbon monoxide per liter of smoke and per cigarette were determined for 10 brands of cigarettes smoked under 27 different conditions (one standard and 26 nonstandard). Per cigarette yields were highly variable across smoking conditions due to differences in the total volume of smoke taken for analysis. The results of a simple linear regression analysis indicated that up to 95% of the variation in tar yield per cigarette could be explained by variations in the total volume of smoke produced per cigarette. Per liter yields for tar, nicotine, and carbon monoxide were almost constant over the conditions investigated. Since most smokers inhale less than this amount, yields per liter provide a rough estimate of the maximum amount to which a smoker might be exposed. Yields per liter, taken over all 26 conditions, are highly correlated with per cigarette yields under standard conditions. Consequently, values on one scale can be converted to the other, at least for the 10 brands investigated. The average conversion factor for tar, nicotine, and carbon monoxide is 2.5 when proceeding from milligrams per king-size cigarette under standard conditions to milligrams per liter. This relationship is true for both vented and nonvented cigarettes when ventilation holes are not blocked.

Passive exposure to tobacco smoke

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Compression fractures of the dorsal spine in hypoglycemic fits in diabetes

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Passive exposure to tobacco smoke: saliva cotinine concentrations in a representative population sample of non-smoking schoolchildren

Saliva cotinine concentrations in 569 non-smoking schoolchildren were strongly related to the smoking habits of their parents. When neither parent smoked the mean concentration was 0.44 ng/ml, rising to 3.38 ng/ml when both parents were cigarette smokers. Mothers' smoking had a stronger influence than did fathers' (p less than 0.01). In addition, there was a small independent effect of number of siblings who smoked (p less than 0.01). The dose of nicotine received from fathers' smoking was estimated as equivalent to the active smoking of 30 cigarettes a year, that from mothers' smoking as equivalent to smoking 50 cigarettes a year, and that from both parents smoking as equivalent to smoking 80 cigarettes a year. This unsolicited burden may be prolonged throughout childhood and poses a definite risk to health.