Newly-published research suggests that as much as 7 per cent of childhood asthma might be linked to the use of paracetamol by mothers during the later stages of pregnancy.
Dr Seif Shaheen from Kings College London says that while paracetamol is still the preferred painkiller for women during pregnancy, it would be prudent (as with all medications in pregnancy) not to take it unnecessarily, especially after the 20th week.
His report, published in the journal Clinical and Experimental Allergy, is based on the experiences of 8,500 families taking part in the Children of the 90s study at the University of Bristol.
Of those children – 12.5 per cent were reported as having asthma at six years of age.
During pregnancy the mothers had reported on their use of all medicines, of which paracetamol was the most common. Forty per cent of women took it “sometimes” during the second half of their pregnancy (after 20 weeks), and a tiny percentage reported that they took paracetamol almost every day.
While there was no association with aspirin – the analysis showed a positive association between paracetamol use by the mothers during later pregnancy and asthma and wheezing, but not hayfever or eczema, in their children.
Even after taking account of other factors which might influence the risk of asthma in the child – such as the mother’s history of asthma and allergies, illnesses and smoking during pregnancy, and her socio-economic background, – a significant association with paracetamol use in pregnancy remained.
Women who said they took paracetamol “sometimes” after 20 weeks of pregnancy were 22 per cent more likely than women who never took it to have an asthmatic child. The risk was increased by 62% for women who took it “most days or daily”.
Two years ago Dr Shaheen’s team showed a link between frequent paracetamol use during late pregnancy and an increased risk of wheezing in early childhood,. These latest findings, in the same cohort of children, extend the previous observations and suggest that these effects may persist to school age, when children are old enough for asthma to be formally diagnosed.
In his latest paper Dr Shaheen postulates that paracetamol taken during pregnancy may cause damage to the developing lungs and immune system of the fetus, thus increasing the risk of developing asthma in childhood. However, he emphasises that this is speculation and that we do not know whether such effects can occur when normal doses of paracetamol are taken during pregnancy in humans, nor the exact mechanisms that might be involved.
Dr Shaheen reports: 'While we should be cautious as to whether these findings really represent a causal link, we estimate that the proportion of asthma attributable to paracetamol use in late pregnancy, assuming a causal relation, was 7 per cent'.
'Although the risks associated with moderate use were very small – it is common for mothers to take paracatamol sometimes during late pregnancy'.
'At this stage we can’t determine if there might be a threshold of usage below which there is no associated risk. So we would therefore recommend that, although paracetamol should remain the analgesic of choice throughout pregnancy, it should not be taken unnecessarily, especially after 20 weeks'.
Academic paper reference
Prenatal paracetamol exposure and risk of asthma and elevated immunoglobulin E in childhood. S.O. Shaheen, R. B. Newson, A. J. Henderson, J. E. Headley, F. D. Stratton, R. W. Jones, D. P. Strachan and the ALSPAC Study Team. Clinical & Experimental Allergy. doi: 10.1111/j.1365-2222.2005.02151.x
Notes:
- Last month Children of the 90s reported that increased use of household chemicals could also be connected to the rise in asthma. Researchers found a clear connection between children’s breathing problems and their mothers' use of a range of common products such as bleach, paint stripper and carpet cleaners. See web page
- ALSPAC The Avon Longitudinal Study of Parents and Children (also known as Children of the 90s) is a unique ongoing research project based in the University of Bristol. It enrolled 14,000 mothers during pregnancy in 1991-2 and has followed most of the children and parents in minute detail ever since.
- This study was funded by the Department of Health. Dr Shaheen is currently an Asthma UK Senior Research Fellow. Follow-up of the ALSPAC cohort could not have been undertaken without the continuing financial support of the Medical Research Council, the Wellcome Trust, and the University of Bristol among many others.