Study author Dr. Ehud Keinan explained that the citrus ingredient
is called limonene, and it likely protects against asthma
by "burning" inhaled ozone, which can increase inflammation
in the lungs.
Other scents - such as those emitted from pine trees, geraniums
and roses - contain similar ingredients to limonene, Keinan
said, which may help explain why asthma is much more common
in urban areas that lack vegetation.
"In rural populations, people are very much exposed to these
compounds," he said.
The researcher, who is based at the Technion-Israel Institute
of Technology in Israel, stated that squeezing an orange peel
releases liquid that contains a high concentration of limonene.
He said he has heard stories of people who say they experienced
relief from asthma and other lung diseases after spending
time around limonene.
He added that he and his colleagues, who report their current
findings in the journal Bioorganic & Medicinal Chemistry,
are currently investigating how limonene and similar substances
may help alleviate asthma in humans.
A growing body of research suggests that ozone, which is
a key component of air pollution, can encourage changes in
the body that result in persistent inflammation in the airways.
Limonene helps rid the body of ozone because it reacts with
ozone, muting its toxic effects, Keinan explained.
To investigate whether limonene could protect lungs from
asthma, Keinan and his team induced the symptoms of asthma
in rats, them let them smell limonene or eucalyptol, the key
ingredient in the odor of eucalyptus, which does not react
with ozone.
The researchers checked the rats for asthma symptoms repeatedly
over a period of 20 hours to five days. They found that only
rats exposed to limonene "didn't show any symptoms of the
disease," Keinan said.
These results suggest that inhaling limonene may protect
people from developing asthma, or alleviate symptoms in those
already diagnosed, he noted.
SOURCE: Bioorganic & Medicinal Chemistry, December 8, 2004.
