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1.  A strategy to reduce cardiovascular disease by more than 80% 
BMJ : British Medical Journal  2003;326(7404):1419.
Objectives To determine the combination of drugs and vitamins, and their doses, for use in a single daily pill to achieve a large effect in preventing cardiovascular disease with minimal adverse effects. The strategy was to simultaneously reduce four cardiovascular risk factors (low density lipoprotein cholesterol, blood pressure, serum homocysteine, and platelet function) regardless of pretreatment levels.
Design We quantified the efficacy and adverse effects of the proposed formulation from published meta-analyses of randomised trials and cohort studies and a meta-analysis of 15 trials of low dose (50-125 mg/day) aspirin.
Outcome measures Proportional reduction in ischaemic heart disease (IHD) events and strokes; life years gained; and prevalence of adverse effects.
Results The formulation which met our objectives was: a statin (for example, atorvastatin (daily dose 10 mg) or simvastatin (40 mg)); three blood pressure lowering drugs (for example, a thiazide, a β blocker, and an angiotensin converting enzyme inhibitor), each at half standard dose; folic acid (0.8 mg); and aspirin (75 mg). We estimate that the combination (which we call the Polypill) reduces IHD events by 88% (95% confidence interval 84% to 91%) and stroke by 80% (71% to 87%). One third of people taking this pill from age 55 would benefit, gaining on average about 11 years of life free from an IHD event or stroke. Summing the adverse effects of the components observed in randomised trials shows that the Polypill would cause symptoms in 8-15% of people (depending on the precise formulation).
Conclusion The Polypill strategy could largely prevent heart attacks and stroke if taken by everyone aged 55 and older and everyone with existing cardiovascular disease. It would be acceptably safe and with widespread use would have a greater impact on the prevention of disease in the Western world than any other single intervention.
PMCID: PMC162259  PMID: 12829553
2.  Evaluation of a proposed mixture model to specify the distributions of nuchal translucency measurements in antenatal screening for Down's syndrome 
Journal of Medical Screening  2010;17(1):13-18.
A mixture model of crown–rump length (CRL)-dependent and CRL-independent nuchal translucency (NT) measurements has been proposed for antenatal screening for Down's syndrome. We here compare the efficacy of the mixture model method with the standard method, which uses NT multiple of the median (MoM) values in a single distribution.
A routine antenatal screening programme for Down's syndrome comprising 104 affected and 22,284 unaffected pregnancies.
The ability of NT to distinguish between affected and unaffected pregnancies was compared using the mixture model method and the standard MoM method by using published distribution parameters for the mixture model of NT and parameters derived from these for the standard MoM method. The accuracy of the two methods was compared for NT and maternal age by comparing the median estimated risk with the prevalence of Down's syndrome in different categories of estimated risk.
Using NT alone observed estimates of discrimination using the two methods are similar; at a 70% detection rate the false-positive rates were 12% using the mixture model method and 10% using the MoM method. Risk estimation was marginally (but not statistically significantly) more accurate using the standard MoM method.
The mixture model method offers no advantage over the standard MoM method in antenatal screening for Down's syndrome, is more complicated and less generalizable to other data-sets. The standard MoM method remains the method of choice.
PMCID: PMC3104819  PMID: 20356940
3.  Distribution of nuchal translucency in antenatal screening for Down's syndrome 
Journal of Medical Screening  2010;17(1):8-12.
To determine whether the standard deviation of nuchal translucency (NT) measurements has decreased over time and if so to revise the estimate and assess the effect of revising the estimate of the standard deviation on the performance of antenatal screening for Down's syndrome.
Data from a routine antenatal screening programme for Down's syndrome comprising 106 affected and 22,640 unaffected pregnancies.
NT measurements were converted into multiple of the median (MoM) values and standard deviations of log10 MoM values were calculated in affected and unaffected pregnancies. The screening performance of the Combined and Integrated tests (that include NT measurement) were compared using previous and revised estimates of the standard deviation.
The standard deviation of NT in unaffected pregnancies has reduced over time (from 1998 to 2008) (e.g. from 0.1329 to 0.1105 [log10 MoM] at 12–13 completed weeks of pregnancy, reducing the variance by about 30%). This was not observed in affected pregnancies. Compared with results from the serum, urine and ultrasound screening study (SURUSS), use of the revised NT standard deviations in unaffected pregnancies resulted in an approximate 20% decrease in the false-positive rate for a given detection rate; for example, from 2.1% to 1.7% (a 19% reduction) at a 90% detection rate using the Integrated test with first trimester markers measured at 11 completed weeks' gestation and from 4.4% to 3.5% (a 20% reduction) at an 85% detection rate using the Combined test at 11 completed weeks.
The standard deviation of NT has declined over time and using the revised estimates improves the screening performance of tests that incorporate an NT measurement.
PMCID: PMC3104820  PMID: 20356939
5.  UK Lung Screen (UKLS) nodule management protocol: modelling of a single screen randomised controlled trial of low-dose CT screening for lung cancer 
Thorax  2011;66(4):308-313.
The UK Lung Screen (UKLS) is a randomised controlled trial of the use of low-dose multidetector CT for lung cancer screening. It completed the Health Technology Appraisal (HTA)-funded feasibility stage in October 2009 and the pilot UKLS will be initiated in early 2011. The pilot will randomise 4000 subjects to either low-dose CT screening or no screening. The full study, due to start in September 2012, if progression criteria are met, will randomise a further 28 000 subjects from seven centres in the UK. Subjects will be selected if they have sufficient risk of developing lung cancer according to the Liverpool Lung Project risk model. The UKLS employs the ‘Wald Single Screen Design’, which was modelled in the UKLS feasibility study. This paper describes the modelling of nodule management in UKLS by using volumetric analysis with a single initial screen design and follow-up period of 10 years. This modelling has resulted in the development and adoption of the UKLS care pathway, which will be implemented in the planned CT screening trial in the UK.
PMCID: PMC3063456  PMID: 21317179
Health Economist; imaging/CT MRI etc; lung cancer
6.  Use of blood pressure lowering drugs in the prevention of cardiovascular disease: meta-analysis of 147 randomised trials in the context of expectations from prospective epidemiological studies 
Objectives To determine the quantitative efficacy of different classes of blood pressure lowering drugs in preventing coronary heart disease (CHD) and stroke, and who should receive treatment.
Design Meta-analysis.
Data source Medline (1966-2007).
Study selection Randomised trials of blood pressure lowering drugs recording CHD events and strokes. 108 trials studied differences in blood pressure between study drug and placebo (or control group not receiving the study drug) (“blood pressure difference trials”), and 46 trials compared drugs (“drug comparison trials”). Seven trials with three randomised groups fell into both categories. The results were interpreted in the context of those expected from the largest published meta-analysis of cohort studies, totalling 958 000 people.
Participants 464 000 people defined into three mutually exclusive categories: participants with no history of vascular disease, a history of CHD, or a history of stroke.
Results In the blood pressure difference trials β blockers had a special effect over and above that due to blood pressure reduction in preventing recurrent CHD events in people with a history of CHD: risk reduction 29% (95% confidence interval 22% to 34%) compared with 15% (11% to 19%) in trials of other drugs. The extra effect was limited to a few years after myocardial infarction, with a risk reduction of 31% compared with 13% in people with CHD with no recent infarct (P=0.04). In the other blood pressure difference trials (excluding CHD events in trials of β blockers in people with CHD), there was a 22% reduction in CHD events (17% to 27%) and a 41% (33% to 48%) reduction in stroke for a blood pressure reduction of 10 mm Hg systolic or 5 mm Hg diastolic, similar to the reductions of 25% (CHD) and 36% (stroke) expected for the same difference in blood pressure from the cohort study meta-analysis, indicating that the benefit is explained by blood pressure reduction itself. The five main classes of blood pressure lowering drugs (thiazides, β blockers, angiotensin converting enzyme inhibitors, angiotensin receptor blockers, and calcium channel blockers) were similarly effective (within a few percentage points) in preventing CHD events and strokes, with the exception that calcium channel blockers had a greater preventive effect on stroke (relative risk 0.92, 95% confidence interval 0.85 to 0.98). The percentage reductions in CHD events and stroke were similar in people with and without cardiovascular disease and regardless of blood pressure before treatment (down to 110 mm Hg systolic and 70 mm Hg diastolic). Combining our results with those from two other studies (the meta-analyses of blood pressure cohort studies and of trials determining the blood pressure lowering effects of drugs according to dose) showed that in people aged 60-69 with a diastolic blood pressure before treatment of 90 mm Hg, three drugs at half standard dose in combination reduced the risk of CHD by an estimated 46% and of stroke by 62%; one drug at standard dose had about half this effect. The present meta-analysis also showed that drugs other than calcium channel blockers (with the exception of non-cardioselective β blockers) reduced the incidence of heart failure by 24% (19% to 28%) and calcium channel blockers by 19% (6% to 31%).
Conclusions With the exception of the extra protective effect of β blockers given shortly after a myocardial infarction and the minor additional effect of calcium channel blockers in preventing stroke, all the classes of blood pressure lowering drugs have a similar effect in reducing CHD events and stroke for a given reduction in blood pressure so excluding material pleiotropic effects. The proportional reduction in cardiovascular disease events was the same or similar regardless of pretreatment blood pressure and the presence or absence of existing cardiovascular disease. Guidelines on the use of blood pressure lowering drugs can be simplified so that drugs are offered to people with all levels of blood pressure. Our results indicate the importance of lowering blood pressure in everyone over a certain age, rather than measuring it in everyone and treating it in some.
PMCID: PMC2684577  PMID: 19454737
7.  Disagreements are not substantial. 
BMJ : British Medical Journal  1994;308(6935):1027-1029.
PMCID: PMC2539874  PMID: 8167518
8.  Systematic underestimation of association between serum cholesterol concentration and ischaemic heart disease in observational studies: data from the BUPA study. 
BMJ : British Medical Journal  1994;308(6925):363-366.
OBJECTIVE--To estimate the size of the association between serum concentration of low density lipoprotein cholesterol and mortality from ischaemic heart disease. DESIGN--Prospective study of total serum cholesterol concentration and mortality from ischaemic heart disease in 21,515 men (538 deaths) and study of total cholesterol concentration measured on two occasions an average of three years apart in 5696 men in whom low density lipoprotein cholesterol concentration was also measured on the second occasion. SUBJECTS--Men who attended the medical centre of the British United Provident Association (BUPA) in London between 1975 and 1982. MAIN OUTCOME MEASURE--The difference in mortality from ischaemic heart disease for a 0.6 mmol/l difference in concentration of low density lipoprotein cholesterol after adjustment for, firstly, regression dilution bias, which arises from the random fluctuation of serum cholesterol concentration in people over time, and, secondly, the surrogate dilution effect, which arises because differences in total cholesterol concentration between people reflect smaller differences in low density lipoprotein cholesterol concentration. RESULTS--The observed difference in mortality from ischaemic heart disease associated with a difference of 0.6 mmol/l in total serum cholesterol concentration was 17% but increased to 24% after correction for the regression dilution bias and to 27% (95% confidence interval 21% to 33%) after adjustment for both sources of underestimation, which provides an estimate of the difference in mortality for a true difference of 0.6 mmol/l in low density lipoprotein cholesterol concentration. The association was greater at younger ages. The estimated decrease in mortality from all causes was 6% before and 10% (1% to 17%) after adjustment for the two sources of underestimation. There was no excess mortality from any cause associated with low cholesterol concentration. CONCLUSIONS--The association between serum cholesterol concentration and ischaemic heart disease is materially stronger than directly inferred from prospective studies. This has important implications for the health benefit of achieving low cholesterol concentrations.
PMCID: PMC2539480  PMID: 8124143
9.  By how much and how quickly does reduction in serum cholesterol concentration lower risk of ischaemic heart disease? 
BMJ : British Medical Journal  1994;308(6925):367-372.
OBJECTIVE--To estimate by how much and how quickly a given reduction in serum cholesterol concentration will reduce the risk of ischaemic heart disease. DESIGN--Data on the incidence of ischaemic heart disease and serum cholesterol concentration were analysed from 10 prospective (cohort) studies, three international studies in different communities, and 28 randomised controlled trials (with mortality data analysed according to allocated treatment to ensure the avoidance of bias). MAIN OUTCOME MEASURE--Decrease in incidence of ischaemic heart disease or mortality for a 0.6 mmol/l (about 10%) decrease in serum cholesterol concentration. RESULTS--For men results from the cohort studies showed that a decrease of serum cholesterol concentration of 0.6 mmol/l (about 10%) was associated with a decrease in incidence of ischaemic heart disease of 54% at age 40 years, 39% at age 50, 27% at 60, 20% at 70, and 19% at 80. The combined estimate from the three international studies (for ages 55-64 years) was 38% (95% confidence interval 33% to 42%), somewhat greater than the cohort study estimate of 27%. The reductions in incidence of ischaemic heart disease in the randomised trials (for ages 55-64 years) were 7% (0 to 14%) in the first two years, 22% (15% to 28%) from 2.1-5 years, and 25% (15% to 35%) after five years, the last estimate being close to the estimate of 27% for the long term reduction from the cohort studies. The data for women are limited but indicate a similar effect. CONCLUSIONS--The results from the cohort studies, international comparisons, and clinical trials are remarkably consistent. The cohort studies, based on half a million men and 18,000 ischaemic heart disease events, estimate that a long term reduction in serum cholesterol concentration of 0.6 mmol/l (10%), which can be achieved by moderate dietary change, lowers the risk of ischaemic heart disease by 50% at age 40, falling to 20% at age 70. The randomised trials, based on 45,000 men and 4000 ischaemic heart disease events show that the full effect of the reduction in risk is achieved by five years.
PMCID: PMC2539460  PMID: 8043072
10.  By how much does dietary salt reduction lower blood pressure? II--Analysis of observational data within populations. 
BMJ : British Medical Journal  1991;302(6780):815-818.
OBJECTIVE--To determine whether the estimates of the size of the association between blood pressure and sodium intake derived from studies of individuals within populations can be quantitatively reconciled with our estimates derived from comparisons of the average blood pressure and sodium intake between different populations. DESIGN--Examination of data from 14 published studies that correlated blood pressure recordings in individuals against measurements of their 24 hour sodium intake (within population studies). MAIN OUTCOME MEASURE--Comparison of observed differences in blood pressure per 100 mmol/24 h difference in sodium intake in each within population study with predicted differences calculated from the between population data, after allowing for the underestimation of the true association of blood pressure with sodium intake caused by the large day to day variation in 24 hour sodium intake within individuals. RESULTS--The underestimation bias inherent in the within populations studies reduced the regression slope of blood pressure on single measures of 24 hour sodium intake to between a half and a quarter of the true value (for example, in one study from 6.0 to 2.4 mm Hg/100 mmol/24 h). Estimates from between population comparisons of the regression slope of blood pressure on sodium intake, after adjustment to take this underestimation bias into account, were similar to the values actually observed in the within population studies. CONCLUSION--The within population studies confirm our estimates from between population comparisons of the magnitude of the association between blood pressure and sodium intake.
PMCID: PMC1669173  PMID: 2025704
11.  Insulin-like growth factors and cancer: no role in screening. Evidence from the BUPA study and meta-analysis of prospective epidemiological studies 
British Journal of Cancer  2006;95(1):112-117.
Insulin-like growth factor-1 (IGF-1), insulin-like growth factor-2 (IGF-2), and insulin-like growth factor binding protein-3 (IGFBP-3) were measured in frozen serum samples from 1051 men with cancer and 3142 controls in a nested case–control study from the British United Provident Association (BUPA) study cohort and associations with 14 cancers were examined, including prostate, colorectal, and lung. A meta-analysis of studies on these three cancer sites was also conducted. In the meta-analysis the odds ratio between the highest quartile IGF-1 group and the lowest quartile group was 1.31 (95% confidence interval (CI): 1.03–1.67) for prostate, 1.37 (1.05–1.78) for colorectal and 1.02 (0.80–1.31) for lung cancer, and for IGF-2 it was 0.72 (0.36–1.44) for prostate and 1.95 (1.26–3.00) for colorectal cancer. Results from the BUPA study were consistent with the estimates from the other studies. There were no statistically significant associations with IGFBP-3 and any of the cancer sites considered. Our results suggest that IGF-1, IGF-2, and IGFBP-3 measurements have no value in cancer screening, although IGF-1 and IGF-2 may be of aetiological significance in relation to colorectal and prostate cancer.
PMCID: PMC2360494  PMID: 16804529
cancer screening; meta-analysis; cohort studies; insulin-like growth factors; epidemiology
12.  Value of low dose combination treatment with blood pressure lowering drugs: analysis of 354 randomised trials 
BMJ : British Medical Journal  2003;326(7404):1427.
Objective To determine the average reduction in blood pressure, prevalence of adverse effects, and reduction in risk of stroke and ischaemic heart disease events produced by the five main categories of blood pressure lowering drugs according to dose, singly and in combination.
Design Meta-analysis of 354 randomised double blind placebo controlled trials of thiazides, β blockers, angiotensin converting enzyme (ACE) inhibitors, angiotensin II receptor antagonists, and calcium channel blockers in fixed dose.
Subjects 40 000 treated patients and 16 000 patients given placebo.
Main outcome measures Placebo adjusted reductions in systolic and diastolic blood pressure and prevalence of adverse effects, according to dose expressed as a multiple of the standard (recommended) doses of the drugs.
Results All five categories of drug produced similar reductions in blood pressure. The average reduction was 9.1 mm Hg systolic and 5.5 mm Hg diastolic at standard dose and 7.1 mm Hg systolic and 4.4 mm Hg diastolic (20% lower) at half standard dose. The drugs reduced blood pressure from all pretreatment levels, more so from higher levels; for a 10 mm Hg higher blood pressure the reduction was 1.0 mm Hg systolic and 1.1 mm Hg diastolic greater. The blood pressure lowering effects of different categories of drugs were additive. Symptoms attributable to thiazides, β blockers, and calcium channel blockers were strongly dose related; symptoms caused by ACE inhibitors (mainly cough) were not dose related. Angiotensin II receptor antagonists caused no excess of symptoms. The prevalence of symptoms with two drugs in combination was less than additive. Adverse metabolic effects (such as changes in cholesterol or potassium) were negligible at half standard dose.
Conclusions Combination low dose drug treatment increases efficacy and reduces adverse effects. From the average blood pressure in people who have strokes (150/90 mm Hg) three drugs at half standard dose are estimated to lower blood pressure by 20 mm Hg systolic and 11 mm Hg diastolic and thereby reduce the risk of stroke by 63% and ischaemic heart disease events by 46% at age 60-69.
PMCID: PMC162261  PMID: 12829555
13.  Quantifying effect of statins on low density lipoprotein cholesterol, ischaemic heart disease, and stroke: systematic review and meta-analysis 
BMJ : British Medical Journal  2003;326(7404):1423.
Objectives To determine by how much statins reduce serum concentrations of low density lipoprotein (LDL) cholesterol and incidence of ischaemic heart disease (IHD) events and stroke, according to drug, dose, and duration of treatment.
Design Three meta-analyses: 164 short term randomised placebo controlled trials of six statins and LDL cholesterol reduction; 58 randomised trials of cholesterol lowering by any means and IHD events; and nine cohort studies and the same 58 trials on stoke.
Main outcome measures Reductions in LDL cholesterol according to statin and dose; reduction in IHD events and stroke for a specified reduction in LDL cholesterol.
Results Reductions in LDL cholesterol (in the 164 trials) were 2.8 mmol/l (60%) with rosuvastatin 80 mg/day, 2.6 mmol/l (55%) with atorvastatin 80 mg/day, 1.8 mmol/l (40%) with atorvastatin 10 mg/day, lovastatin 40 mg/day, simvastatin 40 mg/day, or rosuvastatin 5 mg/day, all from pretreatment concentrations of 4.8 mmol/l. Pravastatin and fluvastatin achieved smaller reductions. In the 58 trials, for an LDL cholesterol reduction of 1.0 mmol/l the risk of IHD events was reduced by 11% in the first year of treatment, 24% in the second year, 33% in years three to five, and by 36% thereafter (P < 0.001 for trend). IHD events were reduced by 20%, 31%, and 51% in trials grouped by LDL cholesterol reduction (means 0.5 mmol/l, 1.0 mmol/l, and 1.6 mmol/l) after results from first two years of treatment were excluded (P < 0.001 for trend). After several years a reduction of 1.8 mmol/l would reduce IHD events by an estimated 61%. Results from the same 58 trials, corroborated by results from the nine cohort studies, show that lowering LDL cholesterol decreases all stroke by 10% for a 1 mmol/l reduction and 17% for a 1.8 mmol/l reduction. Estimates allow for the fact that trials tended to recruit people with vascular disease, among whom the effect of LDL cholesterol reduction on stroke is greater because of their higher risk of thromboembolic stroke (rather than haemorrhagic stroke) compared with people in the general population.
Conclusions Statins can lower LDL cholesterol concentration by an average of 1.8 mmol/l which reduces the risk of IHD events by about 60% and stroke by 17%.
PMCID: PMC162260  PMID: 12829554
14.  Risk factor thresholds: their existence under scrutiny 
BMJ : British Medical Journal  2002;324(7353):1570-1576.
PMCID: PMC1123506  PMID: 12089098
15.  Adding free to total prostate-specific antigen levels in trials of prostate cancer screening 
British Journal of Cancer  2000;82(3):731-736.
We used a nested case–control design on data from men in four prospective studies (from the UK, Maryland in the USA, and two from Finland) with available stored serum samples to determine whether there was an advantage in measuring both free prostate-specific antigen (PSA) and total PSA as a potential screening test for prostate cancer. Of these men, 247 were verified through national vital statistics offices as having died of prostate cancer, or having developed the disease, and 953 men who did not develop prostate cancer (controls) were selected, matched to cases for age, study centre and sample storage duration. Fixing the false-positive rate at 1%, the prostate cancer detection rate (sensitivity) over the 3 years following serum collection (based on 14 cancers) increased from an estimated 95% using total PSA to 97% using free and bound PSA (that is, bound to α-antichymotrypsin which together with the free form is total PSA). Over a 6-year period (based on 41 cancers) a similar difference occurred (52% and 56% detection rates respectively). We conclude that there is no material advantage in adding free to total PSA in prostate cancer screening trials. © 2000 Cancer Research Campaign
PMCID: PMC2363306  PMID: 10682690
prostate-specific antigen; free prostate-specific antigen; clinical prostate cancer; population screening
16.  Chlamydia pneumoniae infection and mortality from ischaemic heart disease: large prospective study 
BMJ : British Medical Journal  2000;321(7255):204-207.
To determine whether there is an independent association between infection with Chlamydia pneumoniae and ischaemic heart disease.
Prospective study using a nested case-control design.
Medical centre in London run by BUPA, a private medical organisation.
21 520 professional men aged 35-64 who attended for a medical examination in London between 1975 and 1982.
Main outcome measure
Death from ischaemic heart disease.
The distributions of concentrations of IgG and IgA antibodies to C pneumoniae were similar in the 647 men who subsequently died of ischaemic heart disease and in 1294 age matched controls who did not. There was no material association with heart disease irrespective of the cut-off point chosen to define seropositivity. At a cut-off point that defines 15% of controls as positive, for example, the odds ratios were 1.26 (95% confidence interval 0.95 to 1.68) for IgG and 1.09 (0.82 to 1.43) for IgA.
No material association was found between infection with C pneumoniae and ischaemic heart disease. The size and prospective design of the study and the socioeconomic homogeneity of the cohort minimise both random and systematic error.
PMCID: PMC27436  PMID: 10903649
18.  The tar reduction study: randomised trial of the effect of cigarette tar yield reduction on compensatory smoking. 
Thorax  1995;50(10):1038-1043.
BACKGROUND--Observational and short term intervention studies have reported that smokers of low tar cigarettes inhale more deeply (that is, compensate) than those who smoke high tar cigarettes. To quantify this effect a long term randomised trial was conducted on the effects of switching to low tar cigarettes. METHODS--The trial was carried out between April 1985 and March 1988 among cigarette smokers in the British Civil Service, measuring blood carboxyhaemoglobin (COHb) levels and serum cotinine levels as markers of tobacco smoke intake. Volunteers first switched to a cigarette brand yielding around 10% less tar than their usual brand to identify smokers able to change brand. The 434 subjects who successfully switched were then randomly allocated to one of three groups: (a) "fast reduction" group which changed to a brand of cigarettes with a tar yield of about half that of their usual brand; (b) "slow reduction" group which reduced to the same level in steps over several months; and (c) a control group which continued smoking cigarettes with a tar yield 10% lower than their usual brand. RESULTS--Over the course of the trial cigarette consumption declined slightly in all three groups. In both the "fast reduction" and the "slow reduction" groups, intake of COHb and cotinine was reduced, though not to the same extent as the yield reduction. Comparison of the results before randomisation with those at the end of the trial showed that a reduction in carbon monoxide yield of 45% was associated with a decrease in carbon monoxide intake of 19% (95% confidence interval 14% to 24%) and that a reduction in nicotine yield of 40% was associated with an 11% (6% to 16%) reduction in nicotine intake, reflecting relative intakes of about 1.5 for both carbon monoxide and nicotine in the "fast reduction" group. Results were similar in the "slow reduction" group with a 42% reduction in carbon monoxide yield, a 16% (11% to 22%) reduction in carbon monoxide intake, a 37% reduction in nicotine yield, and a 6% (0% to 13%) reduction in nicotine intake. Estimates of compensation derived from these results were 65% for carbon monoxide, 79% for nicotine, and 62% for tar. CONCLUSIONS--Compensation, demonstrated when switching from a high tar cigarette to a low tar one, was incomplete. Advising people who have failed to give up smoking to switch to low tar cigarettes will reduce the intake of smoke constituents to a small extent. This would be expected to decrease their risk of smoking-related diseases, although by a smaller amount than would be achieved by giving up smoking altogether.
PMCID: PMC475015  PMID: 7491550
19.  Neonatal screening for cystic fibrosis. 
BMJ : British Medical Journal  1998;316(7129):404-405.
PMCID: PMC2665594  PMID: 9492649
20.  Helicobacter pylori infection and mortality from ischaemic heart disease: negative result from a large, prospective study. 
BMJ : British Medical Journal  1997;315(7117):1199-1201.
OBJECTIVE: To determine whether there is an independent association between Helicobacter pylori infection of the stomach and ischaemic heart disease. DESIGN: Prospective study with measurement of IgG antibody titres specific to H pylori on stored serum samples from 648 men who died from ischaemic heart disease and 1296 age matched controls who did not (nested case-control design). SUBJECTS: 21,520 professional men aged 35-64 who attended the British United Provident Association (BUPA) medical centre in London between 1975 and 1982 for routine medical examination. MAIN OUTCOME MEASURE: Death from ischaemic heart disease. RESULTS: The odds of death from ischaemic heart disease in men with H pylori infection relative to that in men without infection was 1.06 (95% confidence interval 0.86 to 1.31). In a separate group of 206 people attending the centre, plasma fibrinogen was virtually the same in those who were positive for H pylori (2.62 g/l) and those who were negative (2.64 g/l). CONCLUSIONS: A study that by its size and design minimised both random error and socioeconomic bias found no relation between H pylori infection and ischaemic heart disease. The validity of the study was shown by its confirmation of the recognised association between H pylori infection and stomach cancer (odds ratio 4.0 (1.9 to 8.2); P < 0.001). Eradication of H pylori infection may greatly reduce the incidence of stomach cancer, one of the most common causes of death from cancer worldwide, but it cannot be expected to have any effect in preventing ischaemic heart disease.
PMCID: PMC2127748  PMID: 9393222
21.  Environmental tobacco smoke exposure and ischaemic heart disease: an evaluation of the evidence. 
BMJ : British Medical Journal  1997;315(7114):973-980.
OBJECTIVES: To estimate the risk of ischaemic heart disease caused by exposure to environmental tobacco smoke and to explain why the associated excess risk is almost half that of smoking 20 cigarettes per day when the exposure is only about 1% that of smoking. DESIGN: Meta-analysis of all 19 acceptable published studies of risk of ischaemic heart disease in lifelong non-smokers who live with a smoker and in those who live with a non-smoker, five large prospective studies of smoking and ischaemic heart disease, and studies of platelet aggregation and studies of diet according to exposure to tobacco smoke. RESULTS: The relative risk of ischaemic heart disease associated with exposure to environmental tobacco smoke was 1.30 (95% confidence interval 1.22 to 1.38) at age 65. At the same age the estimated relative risk associated with smoking one cigarette per day was similar (1.39 (1.18 to 1.64)), while for 20 per day it was 1.78 (1.31 to 2.44). Two separate analyses indicated that non-smokers who live with smokers eat a diet that places them at a 6% higher risk of ischaemic heart disease, so the direct effect of environmental tobacco smoke is to increase risk by 23% (14% to 33%), since 1.30/1.06 = 1.23. Platelet aggregation provides a plausible and quantitatively consistent mechanism for the low dose effect. The increase in platelet aggregation produced experimentally by exposure to environmental tobacco smoke would be expected to have acute effects increasing the risk of ischaemic heart disease by 34%. CONCLUSION: Breathing other people's smoke is an important and avoidable cause of ischaemic heart disease, increasing a person's risk by a quarter.
PMCID: PMC2127675  PMID: 9365294
22.  The accumulated evidence on lung cancer and environmental tobacco smoke. 
BMJ : British Medical Journal  1997;315(7114):980-988.
OBJECTIVE: To estimate the risk of lung cancer in lifelong non-smokers exposed to environmental tobacco smoke. DESIGN: Analysis of 37 published epidemiological studies of the risk of lung cancer (4626 cases) in non-smokers who did and did not live with a smoker. The risk estimate was compared with that from linear extrapolation of the risk in smokers using seven studies of biochemical markers of tobacco smoke intake. MAIN OUTCOME MEASURE: Relative risk of lung cancer in lifelong non-smokers according to whether the spouse currently smoked or had never smoked. RESULTS: The excess risk of lung cancer was 24% (95% confidence interval 13% to 36%) in non-smokers who lived with a smoker (P < 0.001). Adjustment for the effects of bias (positive and negative) and dietary confounding had little overall effect; the adjusted excess risk was 26% (7% to 47%). The dose-response relation of the risk of lung cancer with both the number of cigarettes smoked by the spouse and the duration of exposure was significant. The excess risk derived by linear extrapolation from that in smokers was 19%, similar to the direct estimate of 26%. CONCLUSION: The epidemiological and biochemical evidence on exposure to environmental tobacco smoke, with the supporting evidence of tobacco specific carcinogens in the blood and urine of non-smokers exposed to environmental tobacco smoke, provides compelling confirmation that breathing other people's tobacco smoke is a cause of lung cancer.
PMCID: PMC2127653  PMID: 9365295
23.  Prospective study of effect of switching from cigarettes to pipes or cigars on mortality from three smoking related diseases. 
BMJ : British Medical Journal  1997;314(7098):1860-1863.
OBJECTIVE: To estimate the extent to which cigarette smokers who switch to cigars or pipes alter their risk of dying of three-smoking related diseases-lung cancer, ischaemic heart disease, and chronic obstructive lung disease. DESIGN: A prospective study of 21520 men aged 35-64 years when recruited in 1975-82 with detailed history of smoking and measurement of carboxyhaemoglobin. MAIN OUTCOME MEASURES: Notification of deaths (to 1993) classified by cause. RESULTS: Pipe and cigar smokers who had switched from cigarettes over 20 years before entry to the study smoked less tobacco than cigarette smokers (8.1 g/day v 20 g/day), but they had the same consumption as pipe and cigar smokers who had never smoked cigarettes (8.1 g) and had higher carboxyhaemoglobin saturations (1.2% v 1.0%, P < 0.001), indicating that they inhaled tobacco smoke to a greater extent. They had a 51% higher risk of dying of the three smoking related diseases than pipe or cigar smokers who had never smoked cigarettes (relative risk 1.51; 95% confidence interval 0.96 to 2.38), a 68% higher risk than lifelong non-smokers (1.68; 1.16 to 2.45), a 57% higher risk than former cigarette smokers who gave up smoking over 20 years before entry (1.57; 1.04 to 2.38), and a 46% lower risk than continuing cigarette smokers (0.54; 0.38 to 0.77). CONCLUSION: Cigarette smokers who have difficulty in giving up smoking altogether are better off changing to cigars or pipes than continuing to smoke cigarettes. Much of the effect is due to the reduction in the quantity of tobacco smoked, and some is due to inhaling less. Men who switch do not, however, achieve the lower risk of pipe and cigar smokers who have never smoked cigarettes. All pipe and cigar smokers have a greater risk of lung cancer than lifelong non-smokers or former smokers.
PMCID: PMC2126967  PMID: 9224127
24.  Assessing possible hazards of reducing serum cholesterol. 
BMJ : British Medical Journal  1994;308(6925):373-379.
OBJECTIVE--To assess whether low serum cholesterol concentration increases mortality from any cause. DESIGN--Systematic review of published data on mortality from causes other than ischaemic heart disease derived from the 10 largest cohort studies, two international studies, and 28 randomised trials, supplemented by unpublished data on causes of death obtained when necessary. MAIN OUTCOME MEASURES--Excess cause specific mortality associated with low or lowered serum cholesterol concentration. RESULTS--The only cause of death attributable to low serum cholesterol concentration was haemorrhagic stroke. The excess risk was associated only with concentrations below about 5 mmol/l (relative risk 1.9, 95% confidence interval 1.4 to 2.5), affecting about 6% of people in Western populations. For noncirculatory causes of death there was a pronounced difference between cohort studies of employed men, likely to be healthy at recruitment, and cohort studies of subjects in community settings, necessarily including some with existing disease. The employed cohorts showed no excess mortality. The community cohorts showed associations between low cholesterol concentration and lung cancer, haemopoietic cancers, suicide, chronic bronchitis, and chronic liver and bowel disease; these were most satisfactorily explained by early disease or by factors that cause the disease lowering serum cholesterol concentration (depression causes suicide and lowers cholesterol concentration, for example). In the randomised trials nine deaths (from a total of 687 deaths not due to ischaemic heart disease in treated subjects) were attributed to known adverse effects of the specific treatments, but otherwise there was no evidence of an increased mortality from any cause arising from reduction in cholesterol concentration. CONCLUSIONS--There is no evidence that low or reduced serum cholesterol concentration increases mortality from any cause other than haemorrhagic stroke. This risk affects only those people with a very low concentration and even in these will be outweighed by the benefits from the low risk of ischaemic heart disease.
PMCID: PMC2539477  PMID: 8124144
25.  Relation of urinary cotinine concentrations to cigarette smoking and to exposure to other people's smoke. 
Thorax  1990;45(5):356-361.
The relation of urinary cotinine measurements to tobacco consumption in smokers and to exposure to other people's smoke in non-smokers was studied in 49 smokers and 184 reported non-smokers attending a health screening centre. The median urinary cotinine concentration was 1623 ng/ml in the smokers and 6.1 ng/ml in the non-smokers. In smokers the average urinary cotinine concentration increased with reported habitual cigarette consumption; in non-smokers it increased with the reported total seven day duration of exposure to other people's tobacco smoke. Cotinine concentrations were approximately three times higher in non-smokers living with a spouse or partner who was a smoker than in those living with a non-smoker; their reported duration of exposure to tobacco smoke was also three times higher. Non-smoking subjects who were exposed to any tobacco smoke and who lived with a smoker reported 70% of their exposure to be at home (56% for men and 86% for women); the men reported more exposure at work than non-smoking men who lived with a non-smoker. This study confirms the relation of urinary cotinine to stated tobacco smoke exposure in both smokers and non-smokers and further validates the use of information on the smoking habits of the spouse or partner as a measure of tobacco smoke exposure in epidemiological studies of non-smokers.
PMCID: PMC462471  PMID: 2382242

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