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Smoking may exacerbate the increased risk of a blood vessel bursting
inside the brain (intracerebral stroke) already faced by people with
high blood pressure, according to a new study by Institute researchers.
"Smoking and high blood pressure both increase the risk of
hemorrhagic stroke. Since we found that these two risk factors have a
synergistic effect, quitting smoking and lowering blood pressure will
contribute more to preventing stroke than if this previously unreported
interaction is ignored," said Koshi Nakamura, lead author of the study.
The study found that for every 10 millimeters of mercury (mm Hg)
increase in systolic blood pressure (the top number in a reading),
smokers face an additional 15 percentage point increase in risk of
hemorrhagic stroke (bleeding in the brain), compared with nonsmokers.
"Hemorrhagic stroke is an especially debilitating stroke as about half
of the people who have one die as a result of it, while many survivors
are left with paralysis or other debilitating effects," said Rachel Huxley, a study co-author.
High blood pressure and smoking are both major risk factors for
cardiovascular diseases. Some research suggests they are the first and
second most common contributing factors of death in the world, together
contributing to more than one in five deaths worldwide, said Nakamura,
a visiting research fellow in the Nutrition and Lifestyle Division at The George Institute.
The researchers used data on 563,144 people (82 percent Asian, 35
percent women, and average age 47) in the Asia Pacific Cohort Studies
Collaboration (APCSC) to examine whether smoking increased the risk of
stroke and coronary heart disease in people with high blood pressure.
More than a third (37 percent) of the participants were smokers at
the start of the study. During a median of 6.8 years of follow-up, 746
of the 210 961 smokers and 899 of the 352 183 nonsmokers suffered a
hemorrhagic stroke.
For every 10 mm Hg increase in systolic blood pressure, smokers
faced an 81 percent increase in hemorrhagic stroke risk, while
nonsmokers faced a 66 percent increase in risk - a 15 percentage point
increased risk in smokers than nonsmokers. This effect of smoking on
blood pressure was specific to hemorrhagic stroke as there was no
evidence to indicate a similar effect on the risk of coronary heart
disease or ischemic stroke, researchers said.
Systolic blood pressure (SBP) is the pressure when the heart beats.
The lower number in a blood pressure reading is called the diastolic
blood pressure (DBP) and is the pressure between beats. Normal blood
pressure is defined as SBP below 120 mm Hg and DBP below 80 mm Hg. High
blood pressure is defined as blood pressure of 140 mm Hg systolic
and/or 90 mm Hg diastolic or greater.
Compared with smokers with the lowest systolic blood pressure
readings (120 mm Hg or less), smokers with the highest readings (150 mm
Hg or greater) were 9.32 times more likely to suffer a hemorrhagic
stroke. For nonsmokers, being in the highest versus the lowest SBP
group raised the risk of hemorrhagic stroke by 7.05 times.
Smoking did not appear to exacerbate the impact of systolic blood
pressure on the risk of coronary heart disease or ischemic stroke
(strokes caused by a blood clot).
The researchers speculated that smoking may damage blood vessels in
the brain that are already weakened by high blood pressure. Weakened
blood vessels are prone to rupture and bleeding and hence are
particularly susceptible to hemorrhagic stroke.
The National Health and Medical Research Council of Australia and Pfizer, Inc. partially funded the study.
Editor's Note:
Original news release can be found here.
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