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Babies who sleep on old mattresses are at increased risk of developing asthma later in childhood, research has found.
A study at the University of Auckland is thought to be the first to link asthma to used cot mattresses, the researchers write in the journal Clinical and Experimental Allergy. But they are cautious about the finding.
"Although the explanation for this is not certain," they say, "it could be related to the observation that used mattresses have higher levels of [dust] mite allergen and of endotoxin and other microbial products ...
"Further studies are needed to understand the reasons."
The study involved 871 children born to European mothers in Auckland. It found that 24 per cent suffered from wheezing at 3 1/2 years and 18 per cent at 7 years.
Sleeping on an old mattress in the first year of life showed up as a risk factor for asthma - defined as wheezing within the preceding 12 months.
The study also found associations between antibiotic use and being in day care in the first year of life - and asthma at 7, but not at 3 1/2.
"Attendance at day care increases the likelihood of respiratory tract infections, and our findings again raise the possibility that respiratory infections in early childhood may be a risk factor for the subsequent development of asthma."
One of the researchers, Professor Ed Mitchell, said the study also found maternal smoking had an effect on allergic diseases such as asthma.
It found that while the prevalence of wheezing was not altered by exposure to cats, the presence in the home of a dog in the first year of life increased the risk of wheezing at 3 1/2 and 7. This contradicts other studies, the paper says.
