MONDAY, Aug. 31 (HealthDay News) -- Even a little bit of poison in the air -- the smoke from a couple of cigarettes, traces of carbon monoxide from auto exhaust -- can do a lot more damage to the heart and lungs than most people think, two new studies show.
One study finds that the biggest increase in the risk of cardiovascular disease comes from smoking three or fewer cigarettes a day. The other finds a marked association between levels of carbon monoxide well below those set by environmental standards and hospital admissions for heart problems among the elderly. Both are published in the Aug. 31 issue of Circulation.
"What motivated our study was not so much cigarette smoking, but the damage done by secondhand smoke," said the author of the first report, C. Arden Pope III, a professor of epidemiology at Brigham Young University in Provo, Utah. "One of the criticisms of the secondhand smoke issue, as well as the air pollution issue, is that it doesn't seem biologically plausible that you can get the kind of effects you see from exposure that is so much smaller than what you get from smoking."
So Pope and his colleagues analyzed data from the American Cancer Society's Prevention Study II, which includes data on more than 1 million adults, as well as other studies of secondhand smoke and air pollution to assess the danger posed by relatively small amounts of smoking.
The idea was to see whether the relationship is a linear one: less smoking exposure, less damage.
The study found that just isn't so. "If you look at cigarette smoking alone, even a few cigarettes a day increase cardiovascular risk by 65 percent," pope said. "If you smoke one or two packs a day, the risk increases by 100 percent. So, most of the increased risk comes from just a few cigarettes a day."
As for secondhand smoke, exposure equivalent to less than one cigarette a day increases the risk of cardiovascular death by 20 percent to 30 percent, the researchers found.
"The exposure-response relationship is linear, but only over a very long scale," Pope said. "If you are a smoker, reducing your smoking helps some, but quitting entirely helps a lot more."
In the second report, researchers at Yale University reviewed hospital records of 9.3 million Medicare enrollees and air pollution records gathered between 1999 and 2005 in 126 U.S. urban counties.
They found that an increase of only one part per million in daily one-hour exposure to carbon monoxide was associated with a nearly 1 percent increase in the risk of hospitalization for cardiovascular disease among people over 65.
The U.S. Environmental Protection Agency's national air quality standard currently sets a limit of 35 parts per million for one-hour daily exposure to carbon monoxide, an odorless gas whose main source in cities is traffic exhaust.
The association between hospital admissions for a wide range of cardiovascular conditions, including heart rhythm disorders and heart failure, persisted when adjustments were made for other traffic-related air pollutants, such as nitrogen dioxide and fine particles.
An accompanying editorial by Annette Peters, an epidemiologist at the German Research Center for Environmental Health, said the new research "makes an important contribution of the assessment of the role of the environment for cardiovascular health."
"The common thread in both is thinking about the air we breathe and what it does to cardiovascular disease," Peters said of the studies.