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Zwangere
vrouwen die roken verhogen de kans op astma bij hun kinderen en zelfs bij de
kleinkinderen.*
Uit een Amerikaans onderzoek onder
ruim 900 kinderen blijkt dat kinderen waarvan de moeders rookten tijdens de
zwangerschap wel 1,5 keer meer kans op astma hadden dan kinderen waarvan de
moeder niet rookte. Als nu de grootmoeder ook tijdens de zwangerschap gerookt
heeft loopt die kans wel op tot 2,6. Zelfs als alleen de grootmoeder gerookt
heeft is die kans bij de kleinkinderen nog altijd 1,8 keer hoger.
Women who
smoke when pregnant may spark asthma in their grandchildren decades later, a new
study discovers.
A child
whose maternal grandmother smoked while pregnant may have double the risk of
developing childhood asthma compared with those with grandmothers who never
smoked, say researchers from the University of Southern California, US. And the
risk remains high even if the child’s mother never smoked. It has been known
for some time that smoking while pregnant can increase the risk of the child
developing asthma, but this is the first time that the toxic effects of
cigarette smoke have been shown to damage the health of later generations. The
researchers believe that the tobacco may be altering which genes are switched
“on” or “off” in the fetus’s reproductive cells, causing changes that
are passed on to future generations. Frank Gilliland, professor of preventative
medicine at the Keck School of Medicine in Los Angeles, US, and colleagues
interviewed the parents of 338 children who had asthma by the age of five and a
control group of 570 asthma-free children. They found that children whose
mothers smoked while pregnant were 1.5 times more likely to develop asthma that
those born to non-smoking mothers. But children whose grandmothers smoked when
pregnant had, on average, 2.1 times the risk of developing asthma than children
with grandmothers who never smoked. Even if the mother did not smoke, but the
grandmother did, the child was still 1.8 times more likely to develop asthma.
Those children whose mother and grandmother both smoked while pregnant had their
risk elevated by 2.6 times. Two-pronged effect Gilliland believes the
trans-generational repercussions of smoking indicate that tobacco chemicals are
having a two-pronged effect: by
directly damaging the female fetus’s immature egg cells - putting
future children at risk - and also by damaging parts of the fetus’s cells that
are responsible for determining which genes will be expressed.
This second
type of effect - called an epigenetic effect - could potentially alter which
genes are expressed
in the child’s immune system which, in turn, Gilliland suspects, may increase
the child’s susceptibility to asthma.
“We did not study epigenetic changes directly, but this is one suggested
mechanism that could account for our findings,” he told.
Stress
hormones But Marcus Pembrey, an epigenetics expert and director of genetics at
the Avon Longitudinal Study of Parents and Children in Bristol, UK, says that
the results Gilliland found were unlikely to have an epigenetic basis. “Since
the effect has passed down the mother’s line, the increase
in asthma risk is more likely to be due to other factors. For example,
the mother can pass stress hormones, metabolites or immune cells (lymphocytes)
to the fetus while it is in utero, so these are more likely to affect the
child’s health later on.” “The epigenetic theory is a bit far-fetched in this
case,” he told. Gilliland admits that one of the limitations of his study was
that the children may have acquired their asthma through passive smoking as a
result of living in a smoky household where their mother, grandmother or other
relatives smoked. “Other studies suggest that in-utero exposure has an
independent effect from second-hand smoke, but second-hand smoke may also play a
role that we could not separate in this study,” he comments, adding that
further studies are needed. Martyn Partridge, chief medical adviser to Asthma UK
says: “The suggestion of an association with grand-maternal smoking is
intriguing and whilst the authors’ postulated explanations for this are very
reasonable, confirmation of the association in other studies should be the next
step.”
Journal
reference:Chest (vol 127, p 1232) (Mei 2005)