A paper published last February caught my eye and has triggered a series of ruminations. Published February 14, 2013 in the British Medical Journal, the paper documents the impact that public smoking bans have had on the rate of preterm births in Belgium. It seems that Belgium gradually introduced smoking bans in public spaces over a period of years. Between January 2007 when smoking in restaurants was banned, and January 2010 when smoking was banned in bars that serve food, the risk of spontaneous preterm delivery fell by annual rate of just over 3%.
Given the other known impacts of second hand smoke and the already documented impact that similar smoking bans have on public health, these data are not surprising.
If you can access ‘figure 1’ from the full text of the paper, you will experience the one ‘graph is worth a thousand words’ thing directly. The graph presents the rate of preterm births over the period of years in question. One can see visual dips in the rate that coincide with the phasing in of each new limitation on public smoking and a resulting reduction in exposure.
Figure 1: Time trend
The very idea that data could present such a convincing argument in support of these smoking bans would be suspect if this were the first trial to tell us that smoking bans have large impacts on public health. Years back there was that Montana study that showed the temporary drop in heart attacks while a smoking ban was in effect, which disappeared once the ban was rescinded. Then there was also the Minnesota study that reported pretty much the same impact. We’ve seen no shortage of papers that tell us how bad second hand smoke is for kids.
Smokers have more psychological problems than non-smokers and they will likely tell you that’s why they need to smoke. It turns out though that people exposed to second hand smoke experience the same increased levels of mental distress as smokers do. Perhaps, though not likely, this is because they hang around smokers?
Kids exposed to second hand smoke have all sorts of cognitive disorders, things like difficulty reading and other school related tasks. Second hand smoke seems to disrupt all sorts of things related to being pregnant and having babies, even to increasing risk of painful periods…
Though once you start making a list, there is no end in sight to how much research has been published on second hand smoke.
While I am on this topic though of premature births and smoking, there are some mathematical calculations that I’ve been meaning to perform for years.
I’ve been meaning to do this ever since the ‘personhood’ initiatives first appeared on our election ballots. Colorado readers will recall them; they would have defined personhood as beginning at the moment of conception. They have not passed as yet. In 2008, Amendment 48 failed to by 73% to 27% percent. In 2010 a similar measure, Amendment 62, failed by roughly 71% to 29%.
These ballot initiatives always bring to mind a lecture in our obstetrics class once upon a time, that touched on the percentage of conceptions that end in spontaneous abortion. That is the percentage of fertilized eggs that end up aborting naturally. I recall our instructor, Dr. Nora Tallman telling us that about 65% do. She apparently was right
While the reported rate of miscarriage is only about 15-20%, this only includes women who knew they were pregnant. Many more miscarriages occur early on in pregnancy before a period is missed. In studies using highly sensitive pregnancy tests, the miscarriage rate, technically called a spontaneous abortion, is actually 60-70%.
Thus it is accurate to say that only about 35% of babies conceived will be born.
That doesn’t include those lost via therapeutic abortion. How many conceptions fit into this last category?
In 2008 there were 70,038 live births in Colorado and 15,960 therapeutic abortions.
Thus if we can recall any mathematics, we can easily calculate an approximation of how many spontaneous abortions occurred in Colorado.
Live births = conceptions minus spontaneous abortions
L= C – (SB)
L= C -.65C
L= .35 C
70,038 = .35C
70038/.35= C = 200,108 conceptions
130,070 spontaneous abortions
So what does this have to do with smoking bans in Belgium? While most causes of spontaneous abortion are genetic, outside of our control, smoking is one of the few significant risk factors for spontaneous abortion that are within our control. Smoking increases risk for a woman having a spontaneous abortion. A 2006 Danish study quantifies this risk to about a 20% increase for every 5 cigarettes smoked per day.
What about second hand smoke?
There is no doubt that exposure to second hand smoke negatively impacts pregnancy. Babies of mothers exposed to second hand smoke are smaller, born earlier, more likely to have congenital abnormalities and more likely to be still born.
By now you can see where I’m leading. I’m wondering how many spontaneous abortions could be prevented by banning smoking in public places. If public smoking bans reduced the frequency of spontaneous abortions by just over 12%, we would save as many conceptions as are lost to therapeutic abortions in Colorado.
We can’t say that for sure though as that last number, the impact smoking bans have on spontaneous abortions still mains elusive.
Measuring exactly how much second hand smoke exposure increases risk of spontaneous abortion is going to be nearly impossible. Most of these pregnancies end before the mother realizes she is pregnant.
By now you should be wondering why we don’t hear more about the link between secondhand smoke and disease? Could it be that the tobacco industry would prefer we not think about it? If you are inclined to conspiracy thoughts like this, you might want to read a 2007 study in the journal Circulation. Even five years ago, it was already well understood that second hand smoke exposure increased risk of cardiovascular disease by 30%. The study authors document via industry internal communications a concerted effort to discredit the science least it hurt tobacco industry revenue.
BMJ. 2013 Feb 14;346:f441. doi: 10.1136/bmj.f441.
Impact of a stepwise introduction of smoke-free legislation on the rate of preterm births: analysis of routinely collected birth data.
Centre for Environmental Sciences, Hasselt University, Agoralaan gebouw D, 3590 Diepenbeek, Belgium.
To investigate the incidence of preterm delivery in the Belgian population after implementation of smoke-free legislation in three phases (in public places and most workplaces January 2006, in restaurants January 2007, and in bars serving food January 2010).
Logistic regression analyses on routinely collected birth data from January 2002 to December 2011.
All live born singleton births delivered at 24-44 weeks of gestation (n = 606,877, with n = 448,520 spontaneous deliveries).
MAIN OUTCOME MEASURES:
Preterm birth (gestational age <37 weeks).
We found reductions in the risk of preterm birth after the introduction of each phase of the smoking ban. No decreasing trend was evident in the years or months before the bans. We observed a step change in the risk of spontaneous preterm delivery of -3.13% (95% CI -4.37% to -1.87%; P<0.01) on 1 January 2007 (ban on smoking in restaurants), and an annual slope change of -2.65% (-5.11% to -0.13%; P=0.04) after 1 January 2010 (ban on smoking in bars serving food). The analysis for all births gave similar results: a step change of -3.18% (-5.38% to -0.94%; P<0.01) on 1 January 2007, and an annual slope change of -3.50% (-6.35% to -0.57%; P=0.02) after 1 January 2010. These changes could not be explained by personal factors (infant sex, maternal age, parity, socioeconomic status, national origin, level of urbanisation); time related factors (underlying trends, month of the year, day of the week); or population related factors (public holidays, influenza epidemics, and short term changes in apparent temperature and particulate air pollution).
Our study shows a consistent pattern of reduction in the risk of preterm delivery with successive population interventions to restrict smoking. This finding is not definitive but it supports the notion that smoking bans have public health benefits from early life.
Hamer, M., et al. In press. Objectively assessed secondhand smoke exposure and mental health in adults. Archives of General Psychiatry. doi:10.1001/archgenpsychiatry.2010.76
Yolton K, Dietrich K, Auinger P, Lanphear BP, Hornung R.
Environ Health Perspect. 2005 Jan;113(1):98-103.
Lei L, Ye L, Liu H, Chen C, Fang Z, Wang L, Hu Y, Chen D.
Eur J Epidemiol. 2008;23(7):475-81. doi: 10.1007/s10654-008-9250-6. Epub 2008 Apr 25.
Jones RK and Kooistra, K., Abortion incidence and access to services in the United States, 2008, Perspectives on Sexual and Reproductive Health, 2011, 43(1):41-50.
Acta Obstet Gynecol Scand. 2006;85(9):1057-65.
Maternal smoking predicts the risk of spontaneous abortion.
Department of Virus, Hormones and Cancer, Institute of Cancer Epidemiology, Danish Cancer Society, Copenhagen, Denmark.
Few studies have examined smoking prior to pregnancy and the occurrence of spontaneous abortion, as most studies have addressed the risk of spontaneous abortion in relation to smoking during pregnancy. However, results are not entirely consistent. The aim of the present study was to assess the risk of spontaneous abortion consideringsmoking prior to pregnancy.
We performed a nested case-control study using prospective data from a population-based cohort comprising 11,088 women aged 20-29 years. From this cohort, women who experienced either a spontaneous abortion (n=343) or who gave birth (n=1,578) during follow-up were selected. Associations between self-reported smoking at enrollment and subsequent spontaneous abortion were analyzed by means of multiple logistic regression.
The risk of spontaneous abortion in relation to pre-pregnancy smoking showed a clear dose-response effect. The adjusted odds ratio (95% confidence interval) for spontaneous abortion among current smokers prior to conception was 1.20 (1.04-1.39) per every extra five cigarettes smoked per day. The increased risk was only present for current smokers. The duration of smoking prior to pregnancy was not a significant predictor for subsequent spontaneous abortion.
The amount of daily smoking prior to pregnancy seems to be associated with an increased risk ofspontaneous abortion, whereas the duration of smoking does not seem to be related to an increased risk of spontaneous abortion.
Pediatrics. 2011 Apr;127(4):734-41. doi: 10.1542/peds.2010-3041. Epub 2011 Mar 7.
Secondhand smoke and adverse fetal outcomes in nonsmoking pregnant women: a meta-analysis.
UK Centre for Tobacco Control Studies, Division of Epidemiology and Public Health, University of Nottingham, Nottingham, United Kingdom. email@example.com
To determine the risk of adverse fetal outcomes of secondhand smoke exposure in nonsmoking pregnant women.
This was a systematic review and meta-analysis in accordance with Meta-analysis of Observational Studies in Epidemiology (MOOSE) guidelines. We searched Medline and Embase (to March 2009) and reference lists for eligible studies; no language restrictions were imposed. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) were estimated by using random-effect models. Our search was for epidemiologic studies of maternal exposure to secondhand smoke during pregnancy in nonsmoking pregnant women. The main outcome measures were spontaneous abortion, perinatal and neonatal death, stillbirth, and congenital malformations.
We identified 19 studies that assessed the effects of secondhand smoke exposure in nonsmoking pregnant women. We found no evidence of a statistically significant effect of secondhand smoke exposure on the risk of spontaneous abortion (OR: 1.17 [95% CI: 0.88-1.54]; 6 studies). However, secondhand smoke exposure significantly increased the risk of stillbirth (OR: 1.23 [95% CI: 1.09-1.38]; 4 studies) and congenital malformation (OR: 1.13 [95% CI: 1.01-1.26]; 7 studies), although none of the associations with specific congenital abnormalities were individually significant. Secondhand smoke exposure had no significant effect on perinatal or neonatal death.
Pregnant women who are exposed to secondhand smoke are estimated to be 23% more likely to experience stillbirth and 13% more likely give birth to a child with a congenital malformation. Because the timing and mechanism of this effect is not clear, it is important to prevent secondhand smoke exposure in women before and during pregnancy.
[PubMed – indexed for MEDLINE]
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Environ Health. 2013 Jan 15;12:6. doi: 10.1186/1476-069X-12-6.
Environmental risk factors of pregnancy outcomes: a summary of recent meta-analyses of epidemiological studies.
Centre for Research in Environmental Epidemiology (CREAL), Barcelona Biomedical Research Park, Dr, Aiguader 88, Barcelona, 08003, Spain. firstname.lastname@example.org
Various epidemiological studies have suggested associations between environmental exposures and pregnancy outcomes. Some studies have tempted to combine information from various epidemiological studies using meta-analysis. We aimed to describe the methodologies used in these recent meta-analyses of environmental exposures and pregnancy outcomes. Furthermore, we aimed to report their main findings.
We conducted a bibliographic search with relevant search terms. We obtained and evaluated 16 recent meta-analyses.
The number of studies included in each reported meta-analysis varied greatly, with the largest number of studies available for environmental tobacco smoke. Only a small number of the studies reported having followed meta-analysis guidelines or having used a quality rating system. Generally they tested for heterogeneity and publication bias. Publication bias did not occur frequently.The meta-analyses found statistically significant negative associations between environmental tobacco smoke and stillbirth, birth weight and any congenital anomalies; PM2.5 and preterm birth; outdoor air pollution and some congenital anomalies; indoor air pollution from solid fuel use and stillbirth and birth weight; polychlorinated biphenyls (PCB) exposure and birth weight; disinfection by-products in water and stillbirth, small for gestational age and some congenital anomalies; occupational exposure to pesticides and solvents and some congenital anomalies; and agent orange and some congenital anomalies.
The number of meta-analyses of environmental exposures and pregnancy outcomes is small and they vary in methodology. They reported statistically significant associations between environmental exposures such as environmental tobacco smoke, air pollution and chemicals and pregnancy outcomes.
[PubMed – in process]
Circulation. 2007 Oct 16;116(16):1845-54.
Tobacco industry efforts undermining evidence linking secondhand smoke with cardiovascular disease.
Division of General Internal Medicine, Department of Medicine, University of California, Davis, USA.
The scientific consensus that secondhand smoke (SHS) increases cardiovascular disease (CVD) risk by 30% is based on epidemiological and biological evidence. The tobacco industry has contested this evidence that SHS causes CVD, but how and why they have done it has not been described.
METHODS AND RESULTS:
About 50 million pages of tobacco industry documents were searched using general keywords and names of industry consultants and scientists. Tobacco industry-funded epidemiological analyses of large data sets were used to argue against an epidemiological association between SHS and CVD and smoke-free regulations, but these analyses all suffered from exposure misclassification problems that biased the results toward the null. More recent industry-funded publications report an increased risk of CVD associated with SHS but claim a low magnitude of risk. When early tobacco industry-funded work demonstrated that SHS increased atherosclerosis, the industry criticized the findings and withdrew funding. RJ Reynolds focused on attacking the biological plausibility of the association between SHS and CVD by conducting indirect platelet aggregation studies, exposure chamber experiments, and literature reviews. Although these studies also suffered from exposure misclassification problems, several produced results that were consistent with a direct effect of SHS on blood and vascular function. Instead, RJ Reynolds attributed these results to an unproven epinephrine-related stress response from odor or large smoke exposure, which supported their regulatory and “reduced-harm” product development efforts. Philip Morris’ recent “reduced-harm” efforts seem supportive of a similar corporate agenda.
The tobacco industry attempted to undermine the evidence that SHS causes CVD to fight smoke-free regulations while developing approaches to support new products that claim to reduce harm. The industry interest in preserving corporate viability has affected the design and interpretation of their cardiovascular studies, indicating the need for great caution in current debates about future tobacco industry regulation and development of reduced-harm tobaccoproducts.
[PubMed – indexed for MEDLINE]
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