Australasian Science: Australia's authority on science since 1938

Radical Reasons Explain Why Smoking Harms Babies

Credit: freshidea

Credit: freshidea

By Brian Oliver & Hui Chen

New research has found why mothers who smoke or are exposed to second-hand tobacco smoke can cause permanent damage to the health of their babies.

One billion people smoke worldwide, and about 800 million of these smokers are men. Smoking is not just an addictive compulsion; it is also a cultural behaviour among men, especially in Asian cultures. In western society, however, smoking is popular among women, especially younger women.

Originally this behaviour was influenced by the tobacco industry’s marketing campaigns, including Hollywood movie stars in the 20th century, while the pursuit of a lean body image makes it hard for young women to give up smoking. This is because smoking itself can suppress appetite, whereas quitting smoking can lead to weight gain. It is now believed that nicotine in the tobacco smoke plays a major role in the appetite control in smokers.

However, the truth behind weight loss in smokers is not loss of fat but loss of muscle. Smoking promotes the growth of fat tissue, especially when smokers frequently drink alcohol and eat energy-dense foods such as hot chips and sausages. Therefore, smoking actually leads to obesity, rather than making them thin.

Smoking is a huge health problem at any time, but during pregnancy the risks also include the unborn child. The quit rate during pregnancy is low, with most women blaming their strong addiction to nicotine. Household exposure to second-hand smoking is also common in certain communities.

While smoking kills both smokers and second-hand smokers, maternal smoking or exposure to second-hand tobacco smoke can cause permanent damage to babies. The immediate impacts include low birth weight, pre-term birth and perinatal death, while the long-term impacts include childhood respiratory conditions such as frequent viral infections and asthma, childhood obesity, and problems in later adulthood such as obstructive lung disease, hypertension, type 2 diabetes and obesity.

Newborns from smoking mothers are much smaller than those from non-smokers. This is mainly due to two reasons:

  • smoking makes pregnant mothers eat less, leading to poor nutrition in both mothers and the developing child; and
  • certain chemicals in the cigarette smoke, such as nicotine and carbon monoxide, can reduce blood supply to the placenta by constricting the blood vessels.

Furthermore, smaller body weight comes with a smaller head, which is associated with lower IQ and learning ability during school age.

Smaller babies also have small lungs due to abnormal lung development. The nicotine inhaled by the smokers can also destroy the lung structure in their babies, resulting in reduced lung function.

Asthma is the most common chronic disease among children. Maternal smoking or even second-hand smoking during pregnancy can increase the chance of early childhood asthma. This association is stronger when mothers continue smoking during the second and third trimesters.

Inflammatory reactions typically occur when people have a lung infection with a virus or bacteria. This typically results in coughing, breathing difficulties, fever and the production of mucous. Using animal models we found that if we look in the lungs of offspring from mothers exposed to smoke,

inflammations occurs even when there if no infection ( We also found similar changes in the offspring’s brain ( Such changes are likely to promote the development of chronic diseases and can make them more vulnerable to infections.

Human studies also supports these observations. Maternal smoking is associated with increased hospitalisation of infants due to a broad range of both respiratory and non-respiratory infections.

Prior to our study it was thought that nicotine caused most adverse effects on the health of mothers and their offspring. When a person smokes, however, additional toxic chemicals and billions of free radicals are inhaled, enter the bloodstream and affect the whole body. Free radicals are highly reactive and can chemically change tissues in the body. For pregnant women, the response to these chemicals extends to the developing child.

We have found that oxidative stress is the molecular process that causes detrimental changes in the offspring of smoking mothers. Does this mean that it’s OK to smoke and take an antioxidant? No, because most antioxidants are not very active so huge doses would have to be taken to see any effects. However, in animal models we have seen that maternal l-carnitine supplementation improves brain health in the offspring of mothers exposed to cigarette smoke (

Australia was the first country to induce plain packaging for tobacco, and has led the world in population-based methods to reduce smoking rates. However, the replacement of traditional tobacco cigarettes with e-cigarettes may lead to increased tobacco smoking, and this is indeed happening in the USA. The popularity of e-cigarettes has risen steadily over the past 10 years. The popular idea is that because e-cigarette fluids contain less chemicals than tobacco leaves, they will also produce less chemicals when vaped. Thus it has been advertised as a safer option.

While e-cigarettes were originally designed as a tool to help smokers quit, e-cigarettes are increasingly used by people who have never smoked. In the US and UK, where vaping nicotine-containing e-cigarettes is legal, large numbers of high school students try e-cigarettes even if they have never smoked tobacco. The sale of e-cigarettes also doubles each year in the US.

In Australia it is illegal to sell e-cigarettes that contain nicotine, and it is also illegal to possess them unless a doctor has prescribed their use as an aid to quit smoking. However, the internet has made it easy to purchase nicotine-containing e-cigarette fluids. It’s estimated that three million Australian are current e-cigarette users; in Victoria, e-cigarette use has doubled each year. As is the case in the US and UK, the majority of e-cigarette users are young people.

Although the use of e-cigarettes to replace tobacco cigarette might be less harmful, it is unlikely to be harmless. It’s still too early to investigate the impact of e-cigarettes on unborn children as they were only introduced into the market in early 2000. At this stage we can only use animal models to show the potential impacts that could happen in humans.

Similar to tobacco smoke, inhaling the vapour of heated e-cigarette fluids can also increase inflammatory reactions in the lungs of both mothers and their offspring. This can happen as early as at birth and during breast feeding. This indicates that these offspring may also have an increased chance of having asthma or a viral infection when they are young.

It’s important to remember that quitting smoking has health benefits at any time. Even when pregnancies are unplanned, quitting smoking or living in a smoke-free environment is still beneficial.

Prof Brian Oliver is head of the Respiratory Molecular Pathogenesis at The University of Technology, Sydney, where Dr Hui Chen is a Senior Lecturer in the School of Life Sciences.