Smoking is a greater cause of death and disability than any single disease, says the World Health Organization. According to their figures, it is responsible for approximately five million deaths worldwide every year. Tobacco smoking is a known or probable cause of approximately 25 diseases, and even the WHO says that its impact on world health is not fully assessed. Heart Attack and Stroke UK studies show that smokers in their 40s and 50s are five times more likely to have a heart attack than non-smokers. Tobacco contributes to the hardening of the arteries, which can then become blocked and starve the heart of blood flow, causing the attack. Often, smokers who develop this will require complex and risky heart bypass surgery. If you smoke for a lifetime, there is a 50% chance that your eventual death will be smoking-related — half of all these deaths will be in middle age. Smoking also increases the risk of having a stroke. According to this report, what does the World Health Organization say?