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 High-density lipoprotein (HDL) cholesterol helps curb the odds of
heart disease by purging blood vessels of debris and lowering levels
of triglycerides - dangerous fats that can make blood thicker,
stickier and more prone to clots.
Researchers studied 6,654 adults and found people exposed to higher
levels of fine and ultrafine particles in traffic pollution tended
to have lower levels of HDL cholesterol in their blood.
“However, this was a fairly small effect - it wasn’t a dramatic
lowering of HDL - so I don’t think this is a huge cause for alarm
beyond what we already know about the dangers of air pollution,”
said lead study author Griffith Bell of the University of Washington
School of Public Health in St. Louis.
Previous research has linked pollution from traffic exhaust to an
increased risk of lung damage and respiratory diseases as well as
cardiovascular disease and stroke.
For the current study, researchers focused on so-called PM 2.5, a
mixture of solid particles and liquid droplets smaller than 2.5
micrometers in diameter that can include dust, dirt, soot and smoke.
They also looked at what’s known as black carbon, a component of
particulate pollution that’s formed by burning various kinds of
fuels.
Study participants were 62 years old on average, and half of them
were current or former smokers. About 16 percent of the participants
took cholesterol-lowering drugs and roughly 45 percent had high
blood pressure. None had cardiovascular disease at the start of the
study period.
Researchers used participants’ home addresses to estimate average
exposure to PM 2.5 and black carbon over 12-month, three-month and
two-week periods in the year 2000.
They also looked at blood levels of HDL cholesterol and another
measure known as HDL particle count, which some scientists believe
may be a more accurate way to assess heart disease risk. Traditional
cholesterol tests focus only on the quantity of cholesterol, but
newer assessments look at the number of particles carrying
cholesterol in the blood.
Over one year, people exposed to more black carbon had lower levels
of HDL cholesterol than participants with little or no exposure to
black carbon. The difference was small, but statistically
meaningful.
Higher black carbon exposure over one year was also associated with
lower HDL particle counts, but this difference was too small to rule
out the possibility that it was due to chance, researchers report in
the journal Arteriosclerosis, Thrombosis, and Vascular Biology.
Over three months, however, the picture looked different.
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In this shorter-term analysis, higher levels of fine particulate
matter were associated with a lower HDL particle count. The slightly
lower level of HDL cholesterol seen with high pollution exposure was
too small a difference to rule out chance, but it was still
comparable to the rise in HDL seen when smokers quit, the
researchers note.
The study wasn’t a controlled experiment designed to prove how
traffic fumes directly influence cholesterol or the risk of heart
disease.
One limitation of the study is the potential for pollutants other
than black carbon or other fine particles to influence HDL, the
authors note. In addition, they only measured HDL once, making it
impossible to see how pollution exposures might impact cholesterol
over time.
“We’re still not totally sure why air pollution might lower HDL, but
it’s possible that inflammatory responses to air pollution might
change some of the proteins in HDL, making it less effective at
protecting the body from cardiovascular disease,” Bell said by
email. “This is still an ongoing area of research, however.”
Previous research, however, has shown ambient air pollution such as
fine particulate matter can cause hardening of the arteries as well
as death from heart disease, said Dr. Frank Gilliland, a researcher
at the Keck School of Medicine at the University of Southern
California in Los Angeles.
Traffic pollutants have also been linked to death from heart disease
in other studies, Gilliland, who wasn’t involved in the current
study, said by email.
“People may want to plan their outdoor activities to avoid areas
within 100 meters of major roads and freeways and-or other highly
polluted areas,” Gilliland said.
SOURCE: http://bit.ly/2oRUwLS Arteriosclerosis, Thrombosis, and
Vascular Biology, online April 13, 2017.
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