Health effects of tobacco
Tobacco use has predominantly negative effects on human health and concern about health effects of tobacco has a long history. Research has focused primarily on cigarette tobacco smoking.Tobacco smoke contains more than 70 chemicals that cause cancer. Tobacco also contains nicotine, which is a highly addictive psychoactive drug. When tobacco is smoked, nicotine causes physical and psychological dependency. Cigarettes sold in underdeveloped countries tend to have higher tar content, and are less likely to be filtered, potentially increasing vulnerability to tobacco smoking related disease in these regions.Tobacco use is the single greatest cause of preventable death globally. As many as half of people who use tobacco die from complications of tobacco use. The World Health Organization (WHO) estimates that each year tobacco causes about 6 million deaths (about 10% of all deaths) with 600,000 of these occurring in non-smokers due to second hand smoke. In the 20th century tobacco is estimated to have caused 100 million deaths. Similarly, the United States Centers for Disease Control and Prevention describes tobacco use as "the single most important preventable risk to human health in developed countries and an important cause of premature death worldwide." Currently, the number of premature deaths in the U.S. from tobacco use per year outnumber the number of workers employed in the tobacco industry by 4 to 1. According to a 2014 review in the New England Journal of Medicine, tobacco will, if current smoking patterns persist, kill about 1 billion people in the 21st century, half of them before the age of 70.Tobacco use leads most commonly to diseases affecting the heart, liver and lungs. Smoking is a major risk factor for infections like pneumonia, heart attacks, strokes, chronic obstructive pulmonary disease (COPD) (including emphysema and chronic bronchitis), and several cancers (particularly lung cancer, cancers of the larynx and mouth, bladder cancer, and pancreatic cancer). It also causes peripheral arterial disease and high blood pressure. The effects depend on the number of years that a person smokes and on how much the person smokes. Starting smoking earlier in life and smoking cigarettes higher in tar increases the risk of these diseases. Also, environmental tobacco smoke, or secondhand smoke, has been shown to cause adverse health effects in people of all ages. Tobacco use is a significant factor in miscarriages among pregnant smokers, and it contributes to a number of other health problems of the fetus such as premature birth, low birth weight, and increases by 1.4 to 3 times the chance of sudden infant death syndrome (SIDS). Incidence of erectile dysfunction is approximately 85 percent higher in male smokers compared to non-smokers.Several countries have taken measures to control the consumption of tobacco with usage and sales restrictions as well as warning messages printed on packaging. Additionally, smoke-free laws that ban smoking in public places such as workplaces, theaters, and bars and restaurants reduce exposure to secondhand smoke and help some people who smoke to quit, without negative economic effects on restaurants or bars. Tobacco taxes that increase the price are also effective, especially in developing countries.In the late 1700s and the 1800s, the idea that tobacco use caused some diseases, including mouth cancers, was initially widely accepted by the medical community. In the 1880s, automation dramatically reduced the cost of cigarettes, tobacco companies greatly increased their marketing, and use expanded. From the 1890s onwards, associations of tobacco use with cancers and vascular disease were regularly reported; a meta-analysis citing 167 other works was published in 1930, and concluded that tobacco use caused cancer. Increasingly solid observational evidence was published throughout the 1930s, and in 1938, Science published a paper showing that tobacco users live substantially shorter lives. Case-control studies were published in Nazi Germany in 1939 and 1943, and one in the Netherlands in 1948, but widespread attention was first drawn by five case-control studies published in 1950 by researchers from the US and UK. These studies were widely criticized as showing correlation, not causality. Follow up prospective cohort studies in the early 1950s clearly found that smokers died faster, and were more likely to die of lung cancer and cardiovascular disease. These results were first widely accepted in the medical community, and publicized among the general public, in the mid-1960s.