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Passive smoking stunts fetal growth and harms unborn babies.

Smoking bans are associated with a “consistent pattern of reduction in the risk of preterm delivery,” finds a study published by bmj today. The study supports the notion that smoking bans have public health benefits from early life and protect unborn babies from the effects of passive smoking.

It has often been argued that prohibition of smoking in public places is an attack on civil liberties. Some leading public figures have campaigned for a lifting of the ban in pubs and clubs.  In 2011 TV chef and publican Antony Worrall Thompson launched an e-petition calling on the government to review the smoking ban.

The publication of this new study today should lead them to reconsider their position.

A key argument in favour of bans on smoking in public places is the potential impact of secondary smoking, or passive smoking, on the unborn child. 

Maternal smoking during pregnancy is associated with a decrease in placental function and can lead to intrauterine growth restriction. The fetus stops growing and the baby is born small and undernourished. 

One way smoking does this is to interfere with the function of mitochondria in placental cells. Mitochondria are the tiny packages in cells that produce the energy needed for function. They are the power-packs making and supplying energy in all our cells and without which the cells cannot function.  By limiting energy availability in the placenta, the fetus is no longer able to obtain sufficient nutrients for growth and the baby is born stunted. 

Exposure to second-hand smoke, passive smoking, has also been found to affect birth outcomes in the same way, yet little is known about the impact of recent smoke-free legislation on birth weight and preterm birth.  A key question for any public health strategy is whether it is producing sufficient benefits. 

To answer this question, a team of researchers, lead by Dr Tim Nawrot from Hasselt University, investigated whether recent smoking bans in Belgium were followed by changes in preterm delivery. In Belgium, smoke-free legislation was implemented in three phases (in public places and most workplaces in January 2006, in restaurants in January 2007, and in bars serving food in January 2010).

The researchers analysed 606,877 live, single-born babies delivered at 24-44 weeks of gestation in Flanders from 2002 to 2011. Preterm birth was defined as birth before 37 weeks.

They found significant 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. This shows that it was more likely to be the bans that had produced the improved outcome.

The results show a reduction in the risk of preterm births of 3.13% on 1 January 2007 (ban on smoking in restaurants), and a further reduction in the risk of 2.65% after 1 January 2010 (ban on smoking in bars serving food). These changes could not be explained by several other factors - both at the individual level, such as mother’s age and socioeconomic status - and at the population level, such as changes in air pollution and influenza epidemics.

Given that even a mild reduction in gestational age has been linked in other studies to adverse health outcomes in early and later life, the current study has important public health implications. As the authors of the report say:

"Our study shows a consistent pattern of reduction in the risk of preterm delivery with successive population interventions to restrict smoking. It supports the notion that smoking bans have public health benefits even from early life. More and more countries in Europe are adopting stricter legislation on smoking in public places. These results underscore the public health benefit of smoking ban policies."

Smoking is the major preventable cause of death in the UK. Sadly, lung cancer has now overtaken breast cancer as a major cause of death in women. Lung cancer death rates have increased by seven per cent among European women since 2009. The UK has the highest female lung cancer rates in Europe. We still have a long way to go in preventing needless deaths from smoking. 

What this study demonstrates is that measures taken to prevent passive smoking have benefits in early life. Babies are at risk from passive smoking. Such public health concern should outweigh arguments about civil liberty and smoking. Banning smoking in public places where it may harm others is a sensible and beneficial approach. Civil liberty is not predicated on freedom to harm others.

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