A study may have discovered why breastfeeding
might help protect children against allergies such as
asthma, scientists have said.
The French research, published in Nature
Medicine, shows female mice exposed to allergens can pass
them directly to their offspring in milk.
This allows the newborns to become "tolerant"
of the substance.
However, in humans, the link between breastfeeding
and reduced asthma risk remains unproven, say experts.
There is some research evidence that being
breastfed lowers the risk of becoming asthmatic but other
studies have failed to find this.
More than 300 million people worldwide
have allergic asthma and some scientists believe exposure
to allergens, or a lack of exposure, at a very young age
may be important in its development.
Asthma happens when the body's own immune
system recognises as "foreign" a common and harmless substance
found in the environment, such as dust mite faeces.
When this substance is inhaled, the immune
reaction can cause inflammation in the airways, narrowing
them and making it harder to breathe.
For many sufferers, this can mean a lifetime
of drugs, both to damp down the immune reaction and to
re-open their constricted airways during an attack.
The researchers, from the INSERM institute
in France, used an allergen called ovalbumin - a protein
found in egg whites.
They allowed the mothers of newborn mice
to breathe in the protein but not their offspring.
Tests confirmed the allergen was then
transferred to the baby mice via breast milk and that
the baby mice developed an immune system tolerance to
This effect happened independently of
the mother's own immune system.
The researchers wrote: "This study may
pave the way for the design of new strategies to prevent
the development of allergic diseases."
Sally Rose, an asthma nurse specialist
at Asthma UK, said: 'While some research does suggest
that breastfeeding may help reduce the chance of babies
developing allergic conditions such as asthma, there are
other studies that contradict this.
"Because breastfeeding provides many proven
benefits for babies, current advice from the Department
of Health, which Asthma UK supports, is that, where possible,
babies should be exclusively breastfed for the first six
months of life."
Dr Charles McSharry, an immunologist from
Glasgow University, said the research did offer a theory
as to why breastfeeding might be beneficial in humans.
However, he said comparing the immune
reactions of mice and humans was difficult.
"It is far more difficult to induce the
kind of immune tolerance they have achieved in mice in
humans, which is a key difference," he said.