We'll spare you the lecture. (Seriously, though. Stamp out that butt and flush the pack, already.) Tobacco use, namely cigarette smoking, is the chief cause of preventable death in the United States. Left unbridled, smoking could kill more than a billion people this century, according to the World Health Organization. That equals the number who would die if a Titanic sank every 24 minutes for the next 100 years, as former U.S. Surgeon General C. Everett Koop so starkly put it at a March press conference.

Still, it may be harder than ever to quit: Three quarters of today's smokers trying to shed the habit are heavily hooked on nicotine, up 32 percent from almost two decades ago, according to research presented at the American College of Chest Physicians' annual meeting in October. So quitting, for most, is not merely a matter of willpower. Nonetheless, the reasons to do so keep amassing—and they're not all about heart disease, lung cancer, or respiratory problems. Here's a few downsides you might not have considered.

1. It fogs the mind. Smoking may cloud the mind, according to accumulating research. A June study in the Archives of Internal Medicine found that smoking in middle age is linked to memory problems and to a slide in reasoning abilities, though these risks appeared lessened for those who'd long quit; this is important, the authors wrote, because other research has shown that people with mild cognitive impairment in midlife develop dementia at an accelerated rate. Their report piggybacks on several focused on the older set: A 2007 analysis of 19 prior studies concluded that elderly smokers face a heightened risk of dementia and cognitive decline, compared with lifelong nonsmokers. And in 2004, researchers reported in Neurology that smoking appeared to hasten cognitive decline in dementia-free elderly smokers, bringing it on several times faster than in their nonsmoking peers.

2. It may bring on diabetes. As if we need any more risk factors for diabetes, an analysis published in the Journal of the American Medical Association last year found that across 25 prior studies, current smokers have a 44 percent greater chance of developing type 2 diabetes than nonsmokers do, and the risk was strongest for those with the heaviest habit, who clocked 20 or more cigarettes per day. In an accompanying editorial, researchers made a striking estimation: That some 12 percent of all type 2 diabetes cases nationwide might be attributable to smoking.

3. It invites infections. In October, the federal Advisory Committee on Immunization Practices made its first ever recommendation that all smokers ages 19 to 64 be added to a short list of candidates for the pneumococcal vaccine. That's because there are very strong data showing that the risk of infection by pneumonia-causing bacteria is substantially greater for smokers than for nonsmokers, says Pekka Nuorti, a medical epidemiologist at the Centers for Disease Control and Prevention. Exactly why is unclear, though there's evidence that smoking may damage the respiratory system's protective mucous membranes, making it easier for infectious organisms to latch on and cause disease, says Nuorti. Other research suggests that smoking may interfere with immunity, compromising people's ability to fight infections, he adds.

Heightened susceptibility to infections, it appears, isn't limited just to those who do the smoking: A May study in Tobacco Control found that children exposed to secondhand smoke at home during early infancy (especially those born prematurely or with a low birth weight) are more prone to a throng of severe illnesses that may land them in the hospital at some point during childhood. The findings were based on an analysis of more than 7,000 Chinese children from 1997 to 2005.

4. It may stultify a sex life. If men want to hop aboard the Viagra bandwagon, mounting evidence suggests that puffing cigarettes might be just their ticket. Smokers are more apt to experience erectile dysfunction than nonsmokers are, and this risk climbs as the number of cigarettes smoked increases. A study in the American Journal of Epidemiology in 2007 tracked more than 7,500 Chinese men with low risk for artherosclerosis, a chief underlying cause of erectile dysfunction, and found that smoking could independently hike a man's chance of wrangling with the sexual condition. Preventing smoking is an "important approach" for cutting the risk of ED, the researchers concluded.

5. It may lead to wrinkles...everywhere. Not only does smoking contribute to premature facial wrinkles, but a 2007 study in the Archives of Dermatology found that it may also lead to wrinkling of skin that rarely sees the light of day—in areas such as the inner arm and perhaps the buttocks.

6. It may hasten menopause. Women who smoke face an increased risk of infertility, and they may experience natural menopause at a younger age than do nonsmokers, according to the 2004 and the 2001 Surgeon General's Reports, respectively. Further evidence: A 2001 animal study in Nature Genetics found that chemicals in cigarette smoke can hurry menopause by killing off egg cells made by ovaries, thereby dwindling the egg cell reserve. Since the timing of menopause is dictated by the size of a woman's egg cell reserve—which is stocked with about a million eggs at birth and vanishes by menopause—anything that speeds up its loss could logically lead to a much earlier onset of fertility troubles, notes Jonathan Tilly, one of the study's authors and director of the Vincent Center for Reproductive Biology at Massachusetts General Hospital. More worrisome: Women who smoke during pregnancy may be compromising not only their own future fertility but the fertility of their unborn daughters. In studies testing that idea, mice exposed to chemicals in cigarette smoke during gestation were born with shrunken egg reserves. "Even under the best-chance scenario—you're a nonsmoker, you're healthy, you're young, you eat well, you're in shape—human fertility isn't 100 percent," says Tilly. "Anything you can do to make it better is certainly worth your while."

7. It may dull vision. Several studies have found a robust link between smoking and eye disease, specifically age-related macular degeneration, which can permanently blur vision or cause blindness. A 2005 review of 17 studies in the journal Eye reported that active smokers may face two to three times the risk for developing the disease experienced by those who have never smoked.

8. It hurts bones. Smoking weakens the body's scaffolding and is a serious risk factor for osteoporosis, according to the National Institute of Arthritis and Musculoskeletal and Skin Diseases. It's been shown to fritter away bone density in postmenopausal women and to hike the risk of hip fractures in both sexes, according to the 2004 Surgeon General's Report. (People who endure hip fractures are 12 to 20 percent more likely to die than those who don't, the Report notes, though there are ways osteoporosis sufferers can protect themselves.) Smokers may also experience slower healing of broken bones and wounded tissues than do nonsmokers.

9. It may injure the insides. Sure, cigarettes may be smooth to inhale, but they can rough up the digestive system, leading to heartburn, peptic ulcers, and possibly gallstones, according to the National Institute of Diabetes and Digestive and Kidney Diseases. What's more, current and former smokers have an elevated risk of developing Crohn's disease, a condition characterized by inflammation in the digestive tract and causing pain and diarrhea, says NIDDK.

10. It may stifle sleep. Feeling groggy despite a night's slumber might be a problem for those who light up: A February study in Chest found that smokers are four times more likely to get nonrestorative sleep than those who don't smoke, and researchers deemed nicotine the likely culprit. They theorized that its stimulant properties deal smokers a double blow, making it difficult to fall asleep and also potentially sending the body into nicotine withdrawal during the night. (Half of the chemical's effect wears off within two hours.) Since inadequate shut-eye can invite health problems, consider forgoing cigarettes for the sake of your sleep.

11. It shaves years—and quality—off life. Men who have never smoked live on average 10 years longer than their peers who smoke heavily, according to an October report in the Archives of Internal Medicine. Moreover, they enjoyed a higher quality of life throughout those extra years, throwing sand in the face of the old smokers' defense that an early death is a small price to pay for a lifetime of pleasure. The study's Finnish authors drew their conclusion after scrutinizing data on more than 1,600 men tracked for nearly 30 years.

12. It's tied to lots of cancers! Not to belabor the point, but tobacco use and smoking have been linked to much more than lung cancer. In September, the CDC released a report estimating that more than 2 million cases of tobacco-related cancers were diagnosed nationwide between 1999 and 2004. Lung and bronchial cancer topped the list, naturally, but other types included stomach, pancreatic, kidney, urinary bladder, and cervical cancer. "We knew this was a big problem and a preventable problem," says Sherri Stewart, the epidemiologist at CDC who led the research. "But when you present the hard numbers, you start to see the profoundness of the problem." Her message: To protect your health, do everything you can to quit.