NEW YORK - Kids with asthma and pollen allergies were more likely to wheeze, cough and have shortness of breath and other asthma symptoms -- even when pollen levels were considered "low" -- in a new study that suggests parents need to be careful in all seasons.
Yale and Brown University researchers tracked more than 400 children with asthma, as well as the daily pollen levels near each child's home, over the course of five years. They found that despite daily maintenance medications, kids with pollen sensitivities were up to 37 per cent more likely to have respiratory symptoms and to need rescue medication when pollen in the air was as low as six to nine grains per cubic meter -- a level the National Allergy Bureau calls low.
"In some respects, it's common sense that if a child is asthmatic and allergic to pollen, when they're exposed to pollen, they would bear some risk of asthmatic symptoms," said lead author Curt DellaValle, of the Yale School of Forestry and Environmental Studies.
"The biggest thing, though, is seeing these effects even with the lowest levels of pollen," he told Reuters Health. "It leads us to believe that parents of these asthmatic children should be aware that even when pollen levels are low, their children will experience asthmatic symptoms."
The researchers were surprised to find, though, that pollen-sensitive kids had fewer symptoms when ragweed pollen was at high levels. DellaValle said it may mean that the children's parents reacted to high pollen reports and took extra precautions.
"It suggested that they modified their children's behavior by keeping them inside, in air conditioning or by using air filters," DellaValle said.
Asthma affects more than 22 million Americans, nearly six million of them children, and the condition most often begins in childhood.
Symptoms can be exacerbated by irritants in the air, both outdoors and indoors, including air pollution, dust, dander and smoke. People with chronic or frequent symptoms may use so-called maintenance medications, taken daily or every other day, as preventives. Severe asthma attacks are usually treated with "rescue" medications, such as inhaled bronchodilators and corticosteroids in injected or pill form.
Previous research has yielded mixed answers about how much of an effect outdoor allergens have in provoking asthma symptoms, DellaValle's team writes in the journal Epidemiology. One problem, they say, is a lack of good data about local pollen levels over time.
DellaValle's team recruited 430 children with asthma between the ages of four and 12 in New York, Connecticut and Massachusetts between 2000 and 2003. Each kid's mother kept a calendar tracking her child's asthma symptoms and use of asthma medications. The researchers also tested the children's blood for sensitivity to pollens from trees, grass and weeds.
To get a better picture of realistic pollen exposures, every year during the Northeast's pollen season -- generally from late March to early October -- the researchers used a model to analyze the amount of pollen within 1.2 miles (two kilometers) of each child's home. They also tracked daily and seasonal weather, foliage, when pollen seasons began and ended and peak pollen periods.
Among kids with sensitivities to particular types of pollen, even small amounts in the air could trigger asthma symptoms.
Children not on maintenance medication who were sensitive to grass pollen, for example, wheezed, coughed and had trouble breathing and other nighttime symptoms when they were exposed to more than two grains per cubic meter of grass pollen.
Kids on daily maintenance therapy and sensitive to weed pollen could have similar symptoms and a need for rescue medication at pollen levels above six to nine grains per cubic meter.
Among the kids sensitive to weed pollen, low-level exposures raised their risk of symptoms by 37 per cent. That compared to a 23 per cent rise in risk during the highest weed-pollen periods -- hinting that kids may have stayed indoors when pollen levels were known to be high, the researchers note.
Pollen levels were not tied to an increase in asthma symptoms in kids without allergies to specific pollens.
While the study expands understanding of how pollen can affect each individual, DellaValle says, more research is needed. Meanwhile, he advises parents to take necessary precautions to protect their asthmatic children who also are allergic to pollen.
"Be aware of the types of activities they are doing outside," he said. "Keep them inside when you know they are at increased risk."