A few days ago I was in Purton, an ancient village in the Cotswolds, just west of London, where people have smoked tobacco since it started arriving from the Virginia Colonies. But on the evening of June 30, in a haze of smoke, the last legal cigarette was stubbed out at the end of a party, called the Last Night for Tobacco, held in the Angel Pub.

Smoking is not a usual topic for this blog, although I do write about risk factors–such as smoking–for diseases, along with their treatment and possible cures. The toxins and particles in smoke are environmental factors that in many smokers can cause a cascade of harmful effects, from triggering cancerous growths to causing damage to the p53 gene and other DNA.

Britain now becomes the 20th nation in the world, give or take, that has instituted a ban on smoking in public places. The trend started with Ireland in 2004. An article in News@Nature.com recently assessed how well this trend, which is becoming a major movement, is doing in terms of improving health.

For me, banning tobacco in the United Kingdom’s bars and restaurants could not have happened soon enough. Coming from California, where tobacco has been banned in public places since 1998, I have always found it shocking to walk into the soupy air of a British pub and suck in the fumes of someone else’s cigarettes. It stings my eyes and makes me cough, among other things. It also makes me wonder, as I sip an Old Speckled Hen or some other frothy ale, how many of the people I’m mingling with will one day end up with diseases caused by smoking–or if deep inside me some subtle shift in my own DNA is under way as a result of breathing in secondhand smoke.

Reportedly, the health impact–that is, the cost of health care–of smoking was a major reason for the British ban. The National Health Service crunched the numbers and determined that the public health hazard and the cost of caring for smokers outweighed the freedom to light up.

Some Brits protested the smoking ban, and many vigils like the one at the Angel Pub were held, but overall, the day went smoothly. This may have had more to do with the distraction of attempted terrorist bombings in London and Glasgow than with a universal acceptance of the ban. Still, Brits I talked to seemed either happy (nonsmokers) or resigned (smokers).

The impact of bans on smoking in different parts of the world is already being felt. For instance, in California, rates of lung and bronchial cancer have decreased four times as fast as in the rest of the United States. Also in California, the bans are credited with helping people quit smoking, as the number of smokers has fallen from 23 percent of the state’s population in 1988 to 13 percent in 2006. (In 1988, antismoking efforts began with pushes such as advertising, which led to a partial ban in 1995; a complete ban took effect in 1998.) In Scotland, cigarette sales fell 8 percent in the first year of its ban; in Ireland, the number of smokers has dropped 5 percent since 2004.

Surprisingly, according to the News@Nature.com article, many gaps remain in the science of how much damage secondhand smoke does to nonsmokers:

But the data supporting the link between second-hand smoke and cardiovascular disease are more controversial. The surgeon general’s report states that “pooled relative risks from meta-analysis indicate a 25-30% increase in risk of coronary heart disease from exposure to second-hand smoke.” Although most epidemiologists think there is a link, it’s the size of the effect that surprises them.

“It seems to me that a 25% increase is not plausible,” says John Bailar, a biostatistician at the National Academy of Sciences in Washington DC, who thinks the effect should be proportional to exposure, as it is for lung cancer. “Regular smoking only increases the risk of cardiovascular disease by 75%, so how could second-hand smoke, which is much more dilute, have an effect one-third that size?” Bailar says that even if a non-smoker took in 10% as much smoke as a smoker, which is a high-end estimate, his increased risk would be only 7.5%.

Supporters of the ban argue that secondhand “sidestream” smoke is actually more toxic per gram of total particulate matter than is smoke inhaled by the person smoking the cigarette. Another explanation is that in some people, the threshold of smoke to trigger disease is small. According to the article,

Despite these concerns, the surgeon general’s report takes a hard line on exposure, stating that there is no “safe” level. According to Terry Pechacek, one of the authors of the report and associate director at the Office on Smoking and Health at the US Centers for Disease Control and Prevention in Atlanta, Georgia: “Exposure to second-hand smoke for even a short time can have adverse health effects–this is not subject to debate. Compounds in tobacco smoke have the ability to cause cancer in humans, it’s just a probabilistic game of whether they will cause death in a certain individual.”

Meanwhile, back in the United States, there are still numerous states where the fog of smoke remains in bars, restaurants, and workplaces. This includes our nation’s capital, Washington, DC, which has no ban. I was there recently in a posh pub in a neighborhood within DC, Georgetown sitting near a woman who was waving her cigarette behind her and in my face–strategically out of the way of her friends. I didn’t say anything, but I did wonder if this cigarette, which she was apparently enjoying, would be the one that would trigger that p53 mutation in her or in one of us in the room.

A nerdy, uncool thought, perhaps, but it’s sad nonetheless that in the country that launched the antismoking movement with the 1964 Surgeon General’s report, the fog remains.

David Ewing Duncan’s website.