NEW YORK - Overweight preschoolers who keep the extra pounds have a heightened asthma risk at age seven, but the baby fat doesn't seem to matter for kids who slim down, a new study suggests.
Researchers found that of more than 2,000 Swedish children they followed to age eight, those who were overweight or obese at age seven were more likely to have asthma than their thinner peers.
That was true whether or not they were overweight earlier in life.
In contrast, children who were heavy as toddlers or at age four, but not at age seven, were no more prone to asthma than kids who'd always been normal-weight.
The good news for parents is that children who are chubby early in life often see their weight "normalize" by school age, according to lead researcher Jessica Ohman Magnusson, of the Karolinska Institute in Stockholm.
But if the extra weight persists after age four, she told Reuters Health in an email, parents may need help in managing their child's weight in a healthy way.
Magnusson and her colleagues say the findings also fail to support the idea that children's excess weight is a cause of asthma.
A number of studies have found that heavy children have a higher risk of asthma, or more severe symptoms. But whether the extra pounds are the cause is not clear.
"We don't think we can say that overweight is causally associated with asthma -- that is, that overweight causes asthma," Magnusson said.
That's because early-childhood pounds were not tied to asthma risk in cases where children eventually became normal-weight, she said. It's possible that other factors, and not weight itself, explain why children who remain heavy have an increased asthma risk.
The findings, reported in the journal Pediatrics, are based on more than 2,000 children followed from birth to age eight.
Overall, six per cent of the eight-year-olds had asthma, while 10 per cent of the kids who were overweight at age seven did.
The researchers then considered other factors -- like parents' history of allergies, and whether a mom smoked during pregnancy. They found that being overweight at age seven was linked to a doubling in the risk of asthma.
That was true of seven-year-olds who'd been normal-weight earlier in life, as well as those who'd been heavy at age four.
At any age, there were around 300 children in the study group who were overweight. But fewer were persistently heavy; 122 children remained overweight from the age of one to age seven.
So parents should feel reassured, Magnusson said, that those early extra pounds often do not last. And based on these findings, children whose weight normalizes may not have an increased asthma risk.