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18 May 2010
Smoking during pregnancy may be linked to teenage obesity

Smoking during pregnancy is a known risk factor for a variety of health problems for the baby, including low birth weight, respiratory issues and even sudden infant death syndrome.

A picture of a women smoking

Now a new study suggests exposure to cigarette smoke in the womb may also contribute to another problem — abdominal obesity in late adolescence.
The research, carried out by an international team including scientists from The University of Nottingham, is published in the latest edition of the journal Obesity.

Dr Zdenka Pausova, one of the study’s two principal investigators, said: “We believe that maternal cigarette smoking during pregnancy plays an important role in the fetal programming of obesity.

“Although we do not know the exact mechanisms, we know that nicotine in cigarette smoke, for example, sets into the baby’s body and stays there in higher quantities and for longer than in the mother’s. Animal studies suggest that nicotine given prenatally could influence certain parts of the brain, including those that control how much and what we eat and how well we burn calories.

“This study provides one more reason for expectant mothers to avoid smoking.”

The researchers targeted adolescence because this is a period when adult distribution of body fat is established. They investigated whether exposure to cigarette smoke in the womb would stimulate the accumulation of abdominal fat during late puberty, when boys and girls typically experience rapid weight gain.

The scientists studied more than 500 teenagers between the ages of 12 and 18, of which half were exposed to maternal cigarette smoke. Those who were exposed weighed about 300 grammes less at birth than their peers, were breastfed for a shorter period of time and were exposed more frequently to secondhand smoke in utero.

Magnetic resonance imaging (MRI) was used to measure two types of fat: subcutaneous — found directly under the skin — and intra-abdominal fat, which surrounds internal organs. The teenagers were interviewed by a certified nutritionist to track their daily energy and nutrient intake and were asked to complete questionnaires about their physical activity.

The scientists measured adiposity — the accumulation of fat — based on the MRI scans. They found that in early puberty, there was no difference in body weight, total body fat, subcutaneous or intra-abdominal fat between those teenagers who were exposed to smoke in the womb and those who were not. In late puberty, however, the exposed teenagers showed significantly higher quantities of subcutaneous fat: 26 per cent higher than their non-exposed peers. The amount of intra-abdominal fat was 33 per cent higher.

“We found that in late puberty, there was quite a profound difference in adiposity,” said Dr Pausova. “This is important as cardiovascular and metabolic disorders related to obesity — usually considered to be diseases of adulthood — are now beginning in adolescence.”
Previous studies have shown a relationship between in-utero exposure to cigarette smoke and total body fat. Research has also shown that this exposure could be linked to obesity in childhood and in the later teenage years. This is the first study to report that this exposure is also associated with higher intra-abdominal fat in late puberty.

Cigarette smoke contains nearly 4,000 chemicals, of which many have been proven to be harmful to the fetus. Exposure to cigarette smoke is considered to be the most common environmental threat to the fetus in industrialised countries.

The research was conducted by a team of scientists from The University of Nottingham, the University of Toronto, McGill University, the Université de Montréal and the Université du Québec à Chicoutimi. Co-principal investigators of the study were Dr Pausova, and Dr Tomas Paus, both formerly of The University of Nottingham, who carried out the work while they were at Nottingham. Dr Pausova is now a scientist at The Hospital for Sick Children in Toronto, Canada. Dr Paus is now a senior scientist at Baycrest in Toronto.

The Hospital for Sick Children (SickKids) is recognised as one of the world’s foremost paediatric health-care institutions and is Canada’s leading centre dedicated to advancing children’s health through the integration of patient care, research and education. Founded in 1875 and affiliated with the University of Toronto, SickKids is one of Canada’s most research-intensive hospitals and has generated discoveries that have helped children globally.

The study was supported by the Canadian Institutes of Health Research, the Heart and Stroke Foundation of Quebec, and the Canada Foundation for Innovation.


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