But experts, including the study's lead author, warn that the reductions in risk are not huge and that cutting down is not as easy as it may seem.
"My advice is smoking cessation since a smoker's risk of getting heart disease or chronic lung disease is much higher than getting lung cancer. And so far no study has shown any benefit from reducing smoking regarding heart or lung disease," said lead author Dr. Nina S. Godtfredsen, senior researcher at the Copenhagen Centre for Prospective Population Studies, Institute of Preventive Medicine in Copenhagen.
Added Thomas Glynn, director of cancer science and trends at the American Cancer Society: "If you are able to successfully reduce your tobacco use you will, in all likelihood, reduce lung cancer risk. But people find it very difficult to reduce their smoking and stay reduced and, secondly, while risk is reduced, it still remains very high."
The new study, along with one that shows that a diet higher in foods containing phytoestrogens -- found in soy products, among other things -- may also lower lung cancer risk, appears in the Sept. 28 issue of the Journal of the American Medical Association. Glynn was not involved with either study.
Lung cancer is the leading cause of cancer deaths worldwide, with almost 90 percent of lung cancer cases related to tobacco. People who quit smoking, no matter at what age, significantly reduce their odds of developing this disease. Nevertheless, many people are unable or unwilling to kick the habit, which is why a concept called "harm reduction" has been gaining popularity.
"Harm reduction reflects the fact that people have a very difficult time stopping smoking, so they are looking for alternatives," Glynn said. "This is furthering the harm-reduction debate. It's a reasonable debate. It pits the quit-or-die people against the just-reduce-and-you'll-reduce-harm people. Unfortunately, it's not as simple as either message."
This observational study involved 11,151 men and 8,563 women aged 20 to 93 in Denmark who underwent physical examinations twice at five- or 10-year intervals between 1964 and 1988. Participants also filled out questionnaires about their lifestyle habits.
The participants were divided into six groups, depending on their smoking habits: continued heavy smokers (15 or more cigarettes a day); reducers (those who reduced from 15 or more cigarettes a day by a minimum of 50 percent but did not quit altogether); continued light smokers (one to 14 cigarettes a day); quitters (those who stopped between the first and second examination); stable ex-smokers; and never smokers.
Compared with persistent heavy smokers, reducers had a 27 percent lower risk of lung cancer; light smokers had a 56 percent lower risk; quitters a 50 percent reduction; stable ex-smokers an 83 percent reduction; and nonsmokers, less than 1 percent.
Still, the best strategy is to quit entirely. A recent study out of Norway found that individuals who cut back to one to four cigarettes a day still had triple the risk of lung cancer and heart disease as non-smokers, Glynn said.
"You can reduce the risk, but you're not going to eliminate it, and you're not going to bring it down very far," Glynn said. "Last year in the U.S., we crossed the threshold: There are now more former smokers than current smokers. People can see there are 47 million people who are now former smokers, so it's not impossible."
Godtfredsen added: "For heavy smokers (15 or more cigarettes a day), halving the cigarette consumption lowers the risk of lung cancer by 25 percent, but the risk is still higher than if you are a lifelong light smoker, and much higher than if you quit smoking."
The second study built on previous research that had shown that use of hormone therapy seemed to lower risk of lung cancer in women and that higher intake of phytoestrogens corresponded with a reduced risk for various types of cancers.
Phytoestrogens are found in soy products, grains, carrots, spinach, broccoli and other fruits and vegetables. They have a weak estrogen-like activity.
Participants included 1,674 lung cancer patients and 1,735 healthy controls. Those with the highest quartiles of phytoestrogen intake had a lower incidence of lung cancer.
The protective effects were seen in current smokers and, to an even greater degree, in never smokers. The authors pointed out, however, that the numbers did not reach statistical significance because of the small numbers of people involved.
The benefits were less pronounced in former smokers.
There seems little doubt that eating a diet high in fruits and vegetables is extremely beneficial. Earlier this month, scientists discovered preliminary evidence indicating that isothiocyanates, a group of compounds found in a wide range of common vegetables, may help slow the development of lung cancer.
More information
For more on quitting smoking, visit the American Cancer Society.
Unexplained weight loss in old age that precedes noticeable memory loss could be an early sign of Alzheimer's disease, according to a new report.
"The most likely explanation is that there is something about these individuals or about this disease that affects body mass index (BMI) before the clinical syndrome becomes apparent -- that loss of BMI reflects the disease process itself," study co-author Dr. David A. Bennett, of the Alzheimer's Disease Center at Rush University Medical Center in Chicago, said in a prepared statement.
The study included 820 people, 65 years and older, who were checked each year for an average of 6.6 years. At the start of the study, none of the volunteers had dementia and their average BMI was 27 (for reference, overweight begins at a BMI of 25 or above, while obesity starts at 30).
During the follow-up period, 151 of the volunteers (18.4 percent) developed Alzheimer's disease.
People who lost about one unit of BMI per year were at a 35 percent greater risk of developing Alzheimer's than those who had no change in BMI during the study, the researchers report. People who had no change in their BMI were at a 20 percent greater risk of developing Alzheimer's than those who gained six-tenths of a unit of BMI per year.
The researchers found a similar relationship between BMI changes and the rate of cognitive decline among the volunteers.
Exact links between unexplained weight loss and Alzheimer's remain unclear.
"Our understanding of Alzheimer's disease is changing as we get more information, particularly when we look at the pathology of the disease," said lead researcher Dr. Aron Buchman, also at Rush. "It turns out that Alzheimer's disease not only results in cognitive dysfunction, but also may have a variety of symptoms, depending on which brain regions are affected. If the disease pathology affects a region of the brain that controls weight, your body mass may decline prior to loss of cognition."
The study appears in the Sept. 27 issue of Neurology.
More information
The U.S. National Institute on Aging has more about Alzheimer's disease.
