Anyone having a baby or who has a baby obviously wants to do whatever they reasonably can and should do to give that baby a good life and keep it healthy. But as human beings we all have various imperfections, and as human beings we have to realize that our knowledge — no matter how good it may seem to be at the moment — is also imperfect and might change as new research emerges.
The study currently in the news has yet to be fully published so it’s difficult to evaluate it completely. It’s a meta-analysis of other studies so it has the advantage of a lot of data, but it also has the disadvantage of blending a lot of different sources and types of data that have different qualities and limitations. Improperly combining data from diverse sources can yield misleading results… particularly if the researchers involved have any predisposing bias toward wanting to produce a particular type of result. This last factor can’t be ignored. While I have no knowledge of these particular researchers or information as to whether the funding might come from a source biased toward promoting smoking bans, the general research climate in this area is such that the factor should not simply be passed off as beneath consideration. (Reference link 1 – Reference link 2)
In considering any possible connection of smoking to SIDS, four different parts of that connection need to be considered: 1) smoking during pregnancy; 2) smoking around an infant in the home; 3) exposing the infant to smoke in public; 4) being very physically near the baby for extended periods (e.g. sleeping with the baby) if you are an active smoker.
No one has ever done a study that suggests either #3 or #4 has any effect on a baby or SIDS. Any expressions along these lines are as ridiculous as saying that a 10 second dip in a wading pool or washing one’s face with a damp rag might drown a person because people are known to drown in water. Actually, the pool and washcloth drowning claims would be more solid because we know without a shadow of a doubt that people drown in water and don’t drown if they’re not in water, and the same cannot be said of smoking or being exposed to normal levels of smoke and SIDS.
Despite this, you’ll see clearly outlandish warnings such as that by "a spokeswoman for the Dept. of Health" in the Sunday Independent article. She is quoted as saying, "We advise parents…. not to share a bed with your baby if you are a smoker." Such a piece of advice has no evidence at all to support it and simply helps to fuel an atmosphere of outright craziness regarding the almost magically deadly properties of tobacco smoke that the antismoking lobby likes to portray.
This leaves us with two main factors that are actually examined in this current study: smoking during pregnancy and exposure to smoke by young infants. These need to be separated because if there is an effect of smoking on SIDS it would be quite possible that one of these factors makes for that effect, while the other one might make no contribution at all. After making that separation, the study’s authors would need to determine if any statistical relationship they found was causal or from lurking variables that are statistically related to smoking instead.
The best way to understand that problem of lurking or masked variables is to look at the famous example of bubblegum chewing and juvenile crime. If a study had been done in Birmingham of bubblegum chewing and another done in London on juvenile crime, there would probably be a very strong link between an increase in bubblegum chewing in Birmingham and an increase in juvenile crime in London five years later. Of course common sense tells us that bubblegum chewing in Birmingham simply could not have caused the crime later in London, so we look for a confounding factor and discover that both cities had a bump in the number of births about 15 years before. Therefore, bubblegum sales went up as the extra number of 10-year-olds started chewing it in Birmingham, while juvenile crime in London went up five years later simply because there were more 15-year-old kids running around loose, testing their boundaries, than in previous years.
The two things could be very strongly linked by statistics… but have no causal link at all! So, when looking at either maternal smoking during pregnancy or secondary smoke exposure after pregnancy and their relation to SIDS rates, we need to remember that a statistical link on its own does not mean causality. It merely shows that there might be a link and the question should be studied more closely.
Until the study itself is fully published and available for examination, there’s no way of knowing how well the authors separated the two factors of maternal smoking and post-birth exposure to smoke, and also no way of knowing how well confounding factors were ruled out.
Years ago, a study like this would have been almost as laughable as a study linking bubblegum and juvenile crime. The solid scientific knowledge hasn’t improved all that much better in the area of SIDS and smoking since then. But today, anyone who simply laughed at such a possible link would probably be considered either ignorant or working for a tobacco company.
Such a possible link is no longer considered ridiculous, but that doesn’t mean that a simple correlation proves causality. We should remember that just five years ago, on April 25th, 2002, Associated Press ran a story about a new study ("SIDS May be Linked to Infection" by Emma Ross), that stated the following: "Researchers told a conference on infectious diseases Thursday that a shock-producing byproduct of E. coli was found in the blood of all SIDS babies tested, but in none of the infants used as a comparison." This indicates that the true cause of SIDS might always be a bacterial infection.
And we should also remember that just last year, in February of 2006, the Guardian ran a story about a US study headlined, "Most cot deaths due to accidental suffocation…". The study found that 85% of SIDS deaths involved positioning that indicated suffocation and another 10% were linked to colds or medication. If that study was correct, then only one SIDS case in 20, just 5%, was due to ALL other possible causes, including smoking and smoke exposure, combined!
Finally, of course, anyone looking at the SIDS/smoking link should read the statements by SIDS folks at:
So does this new study "prove" that mothers who smoke during pregnancy or who smoke in a room with an infant are seriously increasing the risk of that infant dying of SIDS? Probably not: "proof" is a hard criterion to meet.
Does the new study give strong evidence of the above, though? Maybe. We’d have to wait until it came out, analyze its details and methodologies, consider its possible biases, and then make a judgement on that… and such judgements will probably differ depending upon who makes them and what their background prejudices and biases are in this area.
And it’s always important to remember that, at least in the US, the biggest baby boom in history, producing tens of millions of healthy happy babies who went on to land on the moon and enjoy some of the longest lifespans in the history of the world, were largely born into smoking families who always smoked around their babies!