Exposure To Tobacco In Unborn Linked To Increased Risk Of Psychotic Symptoms In Later Adolescence..

A new UK study suggests that exposure to tobacco while in the womb is linked to an increased risk of a child developing psychotic symptoms during their teens.

The study was the work of researchers from Cardiff, Bristol, Nottingham and Warwick Universities and was published in the October issue of the British Journal of Psychiatry.

For the study the researchers looked at data on 6,356 12-year-olds taking part in the Avon Longitudinal Study of Parents and Children, which has been following the health and development of the children of over 14,000 mothers who enrolled during pregnancy in 1991 and 1992.

All the children underwent an interview assessment for psychotic-like symptoms, such as hallucinations or delusions, which revealed that just over 11 per cent of them (734) had definite or suspected symptoms of psychosis.

After analyzing the data, the researchers found a link between how much their mothers smoked in pregnancy and the risk of psychotic symptoms in the children. The link was described as a "dose-response effect" where the more a mother smoked while pregnant, the higher the chance that her child would later develop psychotic symptoms.

The researchers also looked at links between the pregnant mothers' use of alcohol and cannabis and higher risk of psychotic symptoms in their offspring.

They found that drinking alcohol during pregnancy was only linked to higher risk of the offspring developing psychotic symptoms for mothers who had drunk more than 21 units a week during the early stage of pregnancy.

Few mothers said they had smoked cannabis while pregnant, and the researchers found no link between use of this drug and later psychotic symptoms in the children. However this could be due to the low numbers.

The study did not examine the reasons for the link between the mothers' use of tobacco and the raised risk of psychotic symptoms in their offsprings' adolescent years, but the researchers speculated that one reason could be exposure to tobacco in the womb may indirectly affect children's impulse control, attention and thinking.

Between 15 and 20 per cent of pregnant women in the UK smoke tobacco.

Lead author Dr Stanley Zammit, a psychiatrist at Cardiff University's School of Medicine told the media that:

"In our cohort, approximately 19 per cent of adolescents who were interviewed had mothers who smoked during pregnancy."

Zammit said assuming the results were non-biased and did reflect an underlying cause and effect relationship then they would estimate that:

"About 20 per cent of adolescents in this cohort would not have developed psychotic symptoms if their mothers had not smoked."

This would mean that smoking during pregnancy may be an important risk factor for the development of psychotic experiences in the population at large, said Zammit.

In their conclusions, Zammit and colleagues called for further studies to investigate the underlying mechanism by which tobacco exposure may affect the development and function of the unborn child's brain.

"Maternal tobacco, cannabis and alcohol use during pregnancy and risk of adolescent psychotic symptoms in offspring."
Zammit S, Thomas K, Thompson A, Horwood J, Menezes P, Gunnell D, Hollis C, Wolke D, Lewis G and Harrison G.
British Journal of Psychiatry, Oct 2009; 195: 294 - 300.
DOI: 10.1192/bjp.bp.108.062471