Smoking and high blood pressure are a deadly combination that dramatically increase the risk of a blood vessel bursting inside the brain, Australian research shows.

High blood pressure and smoking are known to increase the risk of heart diseases, but Sydney researchers have shown that the two have a stronger "synergistic effect" when both are present.

A study by the George Institute for International Health in Sydney found that smokers with high blood pressure are significantly more likely to suffer from a hemorrhagic stroke, a type of "bleeding" stroke where a blood vessel bursts and bleeds in the brain, than non-smokers with blood pressure problems.

Lead researcher Professor Koshi Nakamura said the revelation should encourage smokers to quit and deal with their blood pressure as well. "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," Prof Nakamura said.

A hemorrhagic stroke is especially debilitating as about half of sufferers die as a result of it, while many survivors are left with paralysis or other crippling effects.

It was the only type of cardiovascular problem where researchers found this heightened risk. Smoking did not appear to exacerbate the impact of blood pressure on the risk of coronary heart disease or ischemic stroke, which was caused by a blood clot.

The researchers believe 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 are therefore particularly susceptible to hemorrhagic stroke, Prof Nakamura said.

The research, published by the American Heart Association, involved 563,144 people of mostly Asian descent.

About 40% of all deaths in Australia each year are caused be heart, stroke and vascular diseases, which is more than any other disease group.

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