Smoking and BP Have Synergy in Risk for Stroke

By Charles Bankhead
CAMPERDOWN, Australia, March 10 -- Smokers who have high blood pressure are at increased risk for hemorrhagic stroke, requiring attention to both risk factors, investigators here said.
A 10 mm Hg rise in systolic blood pressure increased the risk of hemorrhagic stroke by 81% in smokers compared with 66% in nonsmokers (P=0.003), Koshi Nakamura, M.D., of the George Institute for International Health, and colleagues reported in the March issue of Stroke.
Hazard ratios for the effect of systolic blood pressure on coronary heart disease and ischemic stroke were similar, irrespective of smoking status.
"Although quitting smoking and lowering blood pressure are both crucial for prevention of cardiovascular disease, combining the two could be expected to have extra beneficial effect on preventing hemorrhagic stroke," the researchers said.
"Smoking cessation initiatives should be targeted more rigorously for hypertensive patients to prevent hemorrhagic stroke," they added.
Higher blood pressure levels and smoking substantially increase the risk of cardiovascular diseases, including coronary heart disease and stroke. Several studies have shown that smoking and higher blood pressure interact to increase levels of fibrinogen, carotid intima-media thickness, and other markers of increased cardiovascular risk, the authors noted.
Because of the two risk factors' combined effect on those markers, the combination of smoking and elevated blood pressure might have a synergistic effect on cardiovascular events, particularly events associated with atherosclerosis and thrombosis, they theorized.
"If such an interaction exists, multifactorial interventions aimed at both lowering blood pressure and quitting smoking will contribute more to reducing [cardiovascular disease] than expected from past data where their interaction has not been quantified," the authors said.
They examined the relationships among smoking, systolic blood pressure, and cardiovascular events in 41 cohorts comprising a total of 563,144 participants (82% Asian). The mean age of participants was 47, and 37% were smokers at enrollment.
During almost seven years of follow-up, 4,344 coronary events and 5,906 strokes were documented. The data suggested a log-linear relationship between systolic blood pressure and coronary heart disease in smokers and nonsmokers, the authors reported.
By quartile of systolic blood pressure values, smokers and nonsmokers with the highest blood pressure had a relative risk of 2.27 and 2.20, respectively, compared with the lowest blood pressure quartile.
A 10 mm Hg increase in systolic blood pressure was associated with a 29% increase in coronary risk for smokers and 24% in nonsmokers.
In a subset of 63,941 former smokers from 34 of the 41 cohorts, a 10 mm Hg rise in blood pressure increased coronary risk by 14%.
For hemorrhagic stroke a 10 mm Hg incremental change in blood pressure was associated with a hazard ratio of 1.81 for current smokers (95% CI 1.73 to 1.90) versus 1.66 for nonsmokers (95% CI 1.59 to 1.73).
Similar results emerged from analyses of every subtype of fatal cardiovascular event but not total events.
Former smokers had a hazard ratio of 1.55 (95% CI 1.40 to 1.71).
"Smoking and high blood pressure both increase the risk of hemorrhagic stroke," said Dr. Nakamura. "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."
The authors had no disclosures.
Primary source: Stroke: Journal of the American Heart AssociationSource reference:Nakamura K, et al "Cigarette smoking, systolic blood pressure, and cardiovascular diseases in the Asia-Pacific region" Stroke 2008; DOI:10.116t1/STROKEAHA.107.496752.