Toddlers who share a bed with their parents may have an increased risk of asthma in later childhood, scientists have found.
The study investigated 6,160 mothers and their children in Rotterdam, the Netherlands. Researchers collected information via a questionnaire on wheezing and asthma symptoms every year from the age of one to six years.
They also assessed sleeping patterns at the ages of two and 24 months, using a parental questionnaire. Bed-sharing was defined as the child sharing a bed with either the mother or both parents.
The authors found that children who had bed-shared during infancy (at age two months) did not have a higher risk of wheezing during their first six years of life, or of getting diagnosed with asthma.
However, bed-sharing at the age of 24 months was associated with an increased chance of wheezing subsequently (at ages three to six years), and with an increased chance of being diagnosed with asthma at age six.
This finding could suggest that, rather than bed-sharing causing asthma, parents may take the decision to share a bed with their child if they notice asthma symptoms as a way of monitoring their children.
However, this hypothesis was not confirmed by the analysis, because toddlers who wheezed as infants were not more likely to bed-share at the age of two years than toddlers who had not wheezed in infancy.
"The current study shows that there is an association between toddlers who share a bed with their parents at the age of two years and wheezing and asthma in later childhood," said Dr Maartje Luijk, from Erasmus University Rotterdam in the Netherlands.
"We postulated that the finding may be explained by parents taking the decision to share a bed with their toddler to monitor their asthma symptoms.
"However our results found no associations between pre-existing asthma symptoms in the first two years of life and bed-sharing at the age of 2 years.
"This could suggest that bed-sharing increases the risk of asthma in some way, but this study does not provide causal evidence of this. There could be a number of factors at play here.
"For example, bed-sharing families might be more likely to report wheezing because they are more attentive or aware of their children's breathing.
"Alternatively, families might perceive wheezing as problematic and as something that could lead to sleep problems, which might in turn elicit bed-sharing to better monitor these problems.
"More research is needed to identify the factors that may impact on the development of asthma through bed-sharing," said Luijk.
The study is published in the European Respiratory Journal.
