New evidence connects
nausea
to sense of smell
Based on data from a pilot
study, Stanford researchers hypothesize that the
"morning sickness" many women experience during
pregnancy may be connected to a heightened sense of
smell.
Richard Blum, MD, and
LeRoy Heinrichs, MD, both of gynecology and obstetrics at
Stanford's School of Medicine, have co-authored a new
book that surveys the literature on women's nausea and
vomiting and presents new research to support this
hypothesis. Blum, an emeritus consulting professor, and
Heinrichs, active emeritus professor, have been invited
to speak on the topic of nausea and vomiting in pregnancy
at a Sept. 20-21 conference sponsored by the Pregnancy
branch of the National Institute of Child Health and
Human Development.
"Our research
suggests that almost all of the stimuli for pregnancy
nausea and vomiting are odors," Blum said,
"probably as a result of the hyperacuity of the
olfactory system induced by estrogen, which rises during
pregnancy."
Data from earlier studies
reveal that when women have nausea during pregnancy they
are less likely to miscarry. The finding is thought to
follow from the fact that a healthy placenta produces
estrogen in the early part of a pregnancy; if the
placenta is not producing estrogen -- and therefore not
heightening the woman's olfactory sensitivity to the
point of nausea -- then there is an associated problem
with the pregnancy and thus a greater likelihood of
miscarriage.
In their own research --
clinical studies at Stanford and formal surveys -- the
authors found that women reported smell as a common
trigger for nausea, and that a majority of pregnant women
named smell as a precipitant to their nausea.
"Women have told us
this for eons," said Heinrichs. "They say they
can't stand the smell of cooking foods, particularly
meats, bacon. They often state that the smell of coffee,
perfumes, cigarette smoke, petroleum products -- anything
volatile -- triggers their nausea."
Another study found that
women born infertile and without a sense of smell --
anosmics -- suffered no nausea once they were helped to
conceive and have normal pregnancies.
"Our hypothesis of
olfaction as being important, if not the primary trigger,
for nausea was supported," Heinrichs said. "But
I emphasize that this is pilot data. We're developing
hypotheses here that still need to be tested."
Heinrichs' and Blum's
book, Nausea and Vomiting: Overview, Challenges,
Practical Treatments and New Perspectives, was
compiled by 20 students, 20 faculty members and one
additional co-author. This first comprehensive book on
nausea and vomiting emphasizes the experience of women.
"Women suffer nausea and vomiting -- without regard
to pregnancy -- at a rate three or four times greater
than men," said Blum. "The majority of women
rate it as one of the most painful experiences of their
lives."
According to the
researchers, few aspects of women's health have been as
overlooked by researchers as the frequency and pain of
women's nausea and vomiting, in pregnancy or otherwise.
"Women tend not to
take their nausea and vomiting to a doctor," Blum
said, "and probably for good reason, because there's
not much a doctor can do." Physicians may prescribe
an antiemetic to control vomiting, but these drugs are
"notoriously poor at controlling nausea, which is
the far more frequent and disabling experience,"
Blum added.
Research indicates that:
98 percent of women have experienced nausea, 97 percent
vomiting; 43 percent have experienced nausea three times
in the past six months, with half as many vomiting; 25
percent assign nausea to work stress, anxiety and
nervousness; and half report nausea related to illness,
surgery and dietary change.
Within their book the
researchers suggest numerous potential paths for future
research, including the study of such age-old remedies as
ginger, which, anecdotally, has provided relief for
patients suffering from extreme nausea. Heinrichs is
hesitant to recommend ginger for nausea during pregnancy,
though, because its active agent has been identified as a
mitogen -- something that alters the genome and could
affect the fetus.
In addition to his
professional interest, Heinrichs had a personal interest
that helped him realize the important role of smell in
nausea. His son had for years suffered what appeared to
be motion sickness on airplanes, with no relief provided
by drugs. "One day we were taxiing," Heinrichs
recalled, "and he started being nauseated before we
took off. 'Don't you smell that awful smell?' he asked
me. He meant the fuel. The next trip he took a piece of
peppermint in his mouth before he boarded the plane, and
now he flies all over with no trouble as long as he takes
his peppermint." SR
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