Women who are overweight before they get pregnant are more likely to have children with asthma, a study has suggested.
Mothers who were obese before conceiving were 28 per cent more likely to have a child diagnosed with asthma before the age of three, Japanese researchers found.
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Women who were overweight were also 17 per cent more likely to have a young child with asthma compared with those of a healthy weight.
Some experts have suggested this may be because overweight women produce more of a hormone called leptin, which may make the airways of their unborn child more sensitive.
Co-author Dr Emiko Noguchi, from the University of Tsukuba, said: ‘[These findings] matter because asthma is often a lifelong condition which can disrupt everyday life.’
Asthma is the most common long-term condition among children in the UK, affecting around one in 11 young people.
The study, of more than 67,000 women, was published in the Journal of Allergy and Clinical Immunology.
The women’s pre-pregnancy weight was taken from their medical records or a questionnaire.
While three-quarters had a normal body mass index (BMI), about 7 per cent were overweight before conceiving, and nearly two per cent were obese.
Among the children, 11 per cent had asthma before the age of three.
The higher risk of asthma in the children of obese mothers, compared to those from healthy-weight mothers, was found even after other important factors were taken into account.
These included whether mothers had asthma, which they are more likely to pass on to their children, plus whether they smoked during pregnancy, which makes asthma more likely in children, and the sex of their children, as asthma is more common among boys during childhood.
However, the authors point out that the study was done in Japan, where being overweight is far less common than in the UK.
Researchers also found childhood allergies to cow’s milk and eggs were less common in toddlers and babies born to overweight mothers, with the cause of this unclear.
The study found no link between mothers’ weight and childhood eczema when researchers also looked at this.
But the analysis, done on women recruited for a nationwide Japanese study between 2011 and 2014, backs up previous evidence that asthma is more common among children born to overweight mothers.
It follows research from 2011 which suggested obese pregnant women may put their children at higher risk of developing asthma.
The study, which included almost 130,000 Swedish mothers, found children of very obese women were 57 per cent more likely to develop asthma than children of mothers who were a healthy weight.
Even children whose mothers were slightly overweight, with a BMI between 25 and 30, had a small increased risk of asthma.
On the new findings, Dr Noguchi said: ‘Women should be careful about their weight before pregnancy to reduce their own risk of many conditions, and may also reduce the risk of their child having asthma.’