The comprehensive report will make a strong case for the Government to increase the scope of anti-smoking legislation. It even suggests a possible move to try to ban pregnant women from getting tobacco altogether.
The study, produced by Bristol University's Institute of Child Life and Health, is based on analysis of the evidence of 21 international studies on smoking and cot death. The report, co-authored by Peter Fleming, professor of infant health and developmental physiology, and Dr Peter Blair, senior research fellow, will be published this week in the medical journal Early Human Development.
The report urges the Government "to emphasise the adverse effects of tobacco smoke exposure to infants and among pregnant women". It also warns that this year's ban on smoking in public places must not result in an increased exposure of infants or pregnant woman at home – smoking in their presence should be seen as being "anti-social, potentially dangerous, and unacceptable".
The study points out that many mothers and mothers-to-be have not heeded warnings about smoking and may need to have their access to tobacco restricted. "Given the power that tobacco addiction holds over its victims, there is grave concern as to whether it will be a successfully modifiable risk factor without fundamental changes in tobacco availability to vulnerable individuals," it states.
Scientists are working to the theory that exposure to smoke during the pregnancy or just after birth has an effect on brain chemicals in the foetus or in infants, increasing the risk of SIDS.
The Government is considering whether it should change its advice on smoking. It recommends that pregnant women should not drink alcohol at all, but simply recommends that mothers and fathers "cut smoking in pregnancy".
These findings will add weight to calls from doctors earlier this year for a ban on parents smoking indoors where children are present. Professor Robert West, of University College London, the Government's most senior smoking adviser, said: "We can apply powerful social pressure on parents not to smoke in the house."
Speaking about the new report, Dr Blair said: "If smoking is a cause of SIDS, and the evidence suggests it is, we think that if all parents stopped smoking tomorrow more than 60 per cent of SIDS deaths would be prevented."
According to the Foundation for the Study of Infant Deaths (FSID), at least 300 babies in the UK each year die suddenly and unexpectedly, mostly between the ages of one month and four months. SIDS is the biggest killer of babies over a month old, claiming more deaths than traffic accidents, leukaemia and meningitis put together.
The issue has prompted a number of high-profile criminal convictions against mothers such as Angela Cannings and Sally Clark. Mrs Cannings suffered the deaths of three babies who died in their cribs. Mrs Clark had two infants who were taken by SIDS. Both women were jailed but later had their convictions overturned and were released in 2003. Mrs Cannings, whose family smoked, was too upset by personal matters to comment yesterday on the findings of this latest study. Mrs Clark, a non-smoker, died last March.
Although scientists are still trying to understand precisely why babies die so young, medical research is providing effective steps that parents can take to reduce the risk of it happening.
Anti-smoking messages have provided some benefits: in the past 15 years, researchers found that the proportion of smokers among all pregnant mothers in the UK has fallen from 30 to 20 per cent.
Nevertheless, according to another study, in 1984 57 per cent of babies who died from SIDS had mothers who smoked during pregnancy. This had increased to 86 per cent by 2003. It is thought that the huge rise in the proportion of SIDS mothers who smoke is at least to some degree a result of the Back to Sleep campaign which was launched in 1991, and which appears to have had a dramatic effect in reducing cot death.
The key message of this campaign was that parents should put their baby on its back to sleep. Since then, the number of SIDS deaths has fallen by three-quarters. The proportion of SIDS babies found lying face down has fallen from 89 per cent to 24 per cent.
The campaign has also changed the social profile of parents whose infants have died from SIDS. Before the Back to Sleep campaign, fewer than half were from lower socio-economic classes, considered to be "deprived". Now, this proportion has risen to 74 per cent.
The researchers now believe that laying babies face down has been largely removed as the main reason for SIDS. The remaining primary dangers are exposure to tobacco smoke and other factors possibly linked to deprivation.
"The risk of unexpected infant death is greatly increased by both prenatal and postnatal exposure to tobacco smoke," said Dr Blair. "We should aim to achieve a 'smoke-free zone' around pregnant women and infants.
"Reduction of prenatal exposure to tobacco smoke, by reducing smoking in pregnancy, and of postnatal exposure to tobacco, by not allowing smoking in the home, will substantially reduce the risk of SIDS."
There are a number of theories to explain how smoking could affect the baby. Babies exposed to tobacco could have breathing problems. Lung development in the growing foetus could be hindered. Another theory is that levels of brain chemicals are affected by smoke exposure.
"Exposure to tobacco smoke, either prenatally or postnatally, will lead to a complex range of effects upon normal physiological and anatomical development in foetal and postnatal life, together with an increased incidence of acute viral infection that places infants at greatly increased risk of SIDS," says the Bristol University study.
Deborah Arnott, the director of ASH, the anti-smoking charity, said that this report should provoke a strong government campaign to highlight the risks of women smoking while pregnant, and of parents smoking in the home.
"Because of other advice on avoiding cot death, smoking has become an increasingly important trigger and we are very concerned that there is a lack of understanding of how important it is," she said.
A YouGov poll commissioned for ASH at the end of August showed only 17 per cent of respondents thought second-hand smoke had a big impact on cot-death risk, and 26 per cent that it had "some impact". But Ms Arnott does not believe the public ban will necessarily increase smoking at home. She added: "About 85 per cent of smoke is invisible and people think it isn't having an impact if they smoke in a room where the baby isn't, but it moves around the house. Our advice is, if you have a baby and cannot give up, don't smoke in the home or car and use nicotine gum or patches for cravings. Being realistic, banning smoking in the home isn't something we can do."
Catherine Parker-Littler, a midwife and founder of midwivesonline.com, said that her confidential service has received emails from smokers who lost infants to cot death. "In our 'Ask a Midwife' service, we have definitely had emails from a small number of parents who smoke about their experience in terms of a cot death," she said. "Some are about feelings of guilt."
A spokeswoman from the Department of Health said: "This is an interesting report which we will study carefully and consider whether we need to change our advice. At the moment, our advice on how best to reduce the chances of cot death is based on the best available scientific evidence. We advise parents to cut out smoking in pregnancy and not to share a bed with your baby if you are a smoker."
Falsely accused: Bereaved – and then tried for murder
The court cases of Angela Cannings and Sally Clark became bywords for miscarriages of justice after both were wrongly convicted of murdering their children.
Ms Cannings, from Salisbury in Wiltshire, was jailed for life in April 2002 after she was found guilty of smothering her two sons, seven-week old Jason in 1991 and 18-week-old Matthew in 1999.
Ms Cannings, 43, maintained her babies died from Sudden Infant Death Syndrome (SIDS) and was eventually freed in 2003. Her marriage has since broken down and she has left the family home. During her appeal, Professor Robert Carpenter, a medical statistics expert, said the babies had been at a "substantially increased risk" of cot deaths because they may have been exposed to cigarette smoke.
"The Cannings family smoked and the children slept prone," he told the Court of Appeal in 2003.
But the link between smoking and cot death is not a certainty, as the case of Sally Clark shows.
Mrs Clark, who died in March at the age of 42, was jailed for life in 1999 for murdering her two sons, eight-week old Harry and 11-week-old Christopher. Her conviction was finally overturned in 2003.
The Clarks were affluent non-smokers, factors that led Professor Sir Roy Meadow, a consultant paediatrician and expert witness in both trials, to wrongly conclude that the chances of two cot deaths in such a family was "one in 73 million".
Mrs Clark was released after a second appeal found her children had died of natural causes. She never recovered from her ordeal.
Ian Griggs
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