PARIS (AFP) - Millions of people around the world who smoke low-tar cigarettes face just the same risk of lung cancer as smokers who puff on medium-tar brands, according to the first major study to compare the health risks of tar ratings.

Death rates from lung cancer among smokers of medium-tar brands -- classified as between 15 to 21 milligrams of tar per cigarette -- were indistinguishable from those who smoked low (eight to 14 mg) or very low brands (seven mg or less), the study says. Those most at risk were smokers who smoked non-filtered high-tar cigarettes, which are rated as having 22 mg or more tar. The peril of dying prematurely from lung cancer for people in the high-tar category was 44 percent higher than in the other groups. The study, published on Saturday in the British Medical Journal (BMJ), compared the smoking habits and mortality from lung cancer among 364,000 men and 576,000 women aged 30 years or more over six years, from 1982-88. The authors suggest that smokers who switch to low-tar cigarettes in the hope of skirting the cancer risk may be dangerously deluding themselves. "Addicted smokers who switch from a higher to lower tar cigarette can maintain their nicotine intake by blocking ventilation holes, increasing the puff volume or the time during which the smoke is retained in the lungs, and smoking more cigarettes. "As a result, the actual dose of toxicants to the smoker may be much higher than is predicted by machine-measured yields," they say. "Changes in inhalation patterns induced by lower tar cigarettes may increase the surface area of the lung exposed to carcinogens in smoke and thus result in greater deposition of submicron-sized particles deep into the airways." The 1980s research project was initiated by the American Cancer Society (news - web sites), yielding a mountain of data that is still being sifted. Lead authors are Jeffrey Harris of Massachusetts General Hospital in Boston and Michael Thun, an epidemiologist at the American Cancer Society in Atlanta. Low-tar cigarettes were introduced in the late 1960s with the advent of ventilation holes in filter tips; in the 1970s, "expanded tobacco" reduced the tar yield further. Those innovations held out the promise -- or so it appeared at the time -- that a safe or at least safer cigarette had been invented. The nicotine-rich tarry byproduct of smoking is implicated, along with a bouquet of toxic gases, in triggering lung cancer, cardiac disease, circulation problems and many other health ailments. Smoking kills around five million people a year and the toll will rise inexorably unless the habit is tackled in developing countries, according to a study published in September by epidemiologists Majid Ezzati of the Harvard School of Public Health and Alan Lopez of the University of Queensland, Australia.

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