A recent study has concluded that
exposure to a common pesticide increases the risk of all-cause mortality and
cardiovascular mortality. Although the study has limitations, its authors call
for urgent follow-up.
The study focused on a class of
pesticides called pyrethroids. People use these chemicals in agriculture and
for residential pest control. Pyrethroids also appear in a range of household
products.
As the
authors of the new study paper explain, pyrethroids are present in
"household and garden insecticides, pet sprays and shampoos, lice
treatments, and mosquito repellents."
Pyrethroids account for around 30%
of all pesticides in use worldwide. Also, because people phased
organophosphates out for residential use, their use of pyrethroids has risen
sharply in recent decades.
Pyrethroids can enter the body via
inhalation, ingestion, or absorption into the skin. Once inside, the body
breaks them down into metabolites and excretes them in urine within a few
hours.
Because of this quick turnaround,
measuring these metabolites in urine is a reliable way of assessing a person's
recent exposure to pyrethroids.
Investigating
pyrethroids
These chemicals are popular because
they are effective against insects and have no short-term impacts on human
health. However, as the authors of the new study explain, "the
consequences of chronic exposure to pyrethroids on long-term health outcomes in
humans remain to be determined."
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Some studies, they say, have
suggested that pyrethroid exposure "may impair neurodevelopment, interfere
with reproductive health, and increase the risk of major chronic diseases, such
as diabetes,
cardiovascular disease, and Parkinson's
disease."
The authors also note that earlier
studies into the impact of pyrethroids on health have had limitations; to date,
there have been no investigations into the links between exposure to these
pesticides and mortality. So, the scientists set out to plug these gaps in our
knowledge.
They have now published their
results in JAMA Internal Medicine.
To investigate, they took data
collected during the National Health and Nutrition Examination Survey. In
total, the team had access to information from 2,116 adults aged 20 or older.
Each participant provided a urine sample at some point between 1999 and 2002,
which provided information about pyrethroid exposure. The researchers followed
the participants until 2015.
Changes to
mortality risk
In total, there were 246 deaths
during the trial period. After adjusting for a range of factors — including
age, sex, ethnicity, socioeconomic status, dietary and lifestyle factors,
smoking status, and body mass index (BMI) — the
researchers identified some significant trends.
They found that people with the
highest levels of pyrethroid metabolite in their urine had a higher risk of
death during the follow-up period.
Individuals with the highest levels
of pyrethroid exposure had a 56% higher risk of dying from any cause than those
with the lowest levels of exposure.
The
researchers also found that those in the highest exposure group had three times
the cardiovascular mortality risk of those in the lowest exposure group.
Conversely, when the researchers
investigated cancer, they
found that those in the highest exposure group had a slightly lower risk of
dying from it. However, this result was not statistically significant.
Overall, the study authors conclude:
"In
this nationally representative sample of [United States] adults, environmental
exposure to pyrethroid insecticides was associated with an increased risk of
all-cause and cardiovascular disease mortality."
Follow-up
needed
The study appears alongside an invited commentary by
Steven D. Stellman, Ph.D., and Jeanne Mager Stellman, Ph.D., both of whom are
from the Columbia University Mailman School of Public Health in New York City,
NY.
The authors discuss certain
limitations. For instance, the average age of the participants at the end of
the study was 57, which is young for assessing pyrethroid's impact on
cardiovascular mortality.
However, they explain, "Other
than cigarette smoking, few, if any, chemical exposures are known to trigger a
[threefold] increase in the risk of death from heart disease, especially in [people] younger than 60
years."
They also
write that "in New York City and elsewhere, aerial spraying for mosquito
control to prevent West Nile virus and other vector-borne illnesses is largely
based on pyrethroids. This study challenges the assumption that such exposures
are safe."
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