Thirdhand Smoke Damages Human Cells
Thirdhand smoke, the residue from cigarette smoke that lingers on surfaces and in dust long after the cigarette is out and the smoke has cleared, may damage human cells, a new study finds.
The researchers used two standard laboratory tests to assess the toxicity of thirdhand smoke. They showed that a compound found in smoke residue, called tobacco-specific nitrosamine, significantly damages DNA in human cells.
"This is the very first study to show that thirdhand smoke is mutagenic and causes DNA damage, which is considered as one of the first steps toward cancer," said study researcher Lara Gundel, of Lawrence Berkeley National Laboratory in California.
Though the harmful effects of cigarette smoking are well-known, the question of whether exposure to thirdhand smoke is also a health concern has often been overlooked, the researchers said.
Thirdhand smoke is the smell that remains on the clothes and hair of someone who has just smoked, or the odor left in hotel rooms where smokers stayed. The chemicals are derivatives of nicotine, and remain in indoor environments, absorbed in the fabric of curtains and carpeting, and on the surface of other objects.
However, the extent to which the chemicals could be hazardous to people is still unknown.
"The purpose of the study was to find how toxic and hazardous some compounds in thirdhand smoke are, and by what mechanisms they can cause harm," Gundel said.
In the study, the researchers put paper strips in smoking chambers. Some of the samples were left for only 20 minutes, after which the researchers measured the residue; the researchers called this "acute exposure." Other strips were left for nearly 200 days in a smoking chamber that was ventilated, to create a "chronic exposure" condition.
The researchers then extracted the chemicals from the paper strips, and exposed cells to the chemicals.
The results showed that the chronic samples had a higher concentration of thirdhand smoke residue than the acute samples. The chronic samples also caused higher levels of DNA damage.
"The cumulative effect of thirdhand smoke is quite significant," Gundel said. "The findings suggest the materials could be getting more toxic with time."
One important characteristic of thirdhand smoke is that its residue can interact with compounds in the air, such as ozone, and produce new toxins, the researchers said.
It is difficult to say when it is safe to enter a place where a smoker has formerly lived, as the emission seems to continue for a long time.
Cleaning a home or a car that has been smoked in doesn't seem to solve the problem. The researchers said they encountered people who complained about buying a used car that didn't smell at first but after a few days started to smell as if somebody had smoked in it.
"Even when you paint the walls, it covers the smell for a short time, but then the compounds work their way through the painting," Gundel said.
"We can take up markers from former smoking months, and sometimes even years after the smoker has left," the researchers said.
Future studies should investigate the effects of nitrosamines and other compounds found in thirdhand smoke on people by looking at blood samples, the researchers said.
The study was published June 13 in the journal Mutagenesis, and was funded by the Tobacco-Related Disease Research Program, which is managed by the University of California and funded by state cigarette taxes.
Infections Linked to Mood Disorders
Infections and autoimmune disorders may increase the risk of developing a mood disorder such as depression later in life, a new study from Denmark suggests.
In the study, which included more than 3 million people, those who were hospitalized for infections were 62 percent more likely to subsequently develop a mood disorder compared with people not hospitalized for infections. And those hospitalized for an autoimmune disease were 45 percent more likely to subsequently develop a mood disorder. Autoimmune diseases are those in which the immune system goes awry and attacks the body's own cells or tissues.
The risk of mood disorders increased with the number of times a person was hospitalized. Those who were hospitalized three times with infections during the study had double the risk of a mood disorder, and those who were hospitalized seven times had triple the risk, compared to those not hospitalized with infections.
The findings support the hypothesis that inflammation, from either an infection or autoimmune disease, may affect the brain in a way that raises the risk of mood disorders, the researchers say.
If the link is confirmed in further studies, the researchers said, their estimates show that infections could be responsible for up to 12 percent of mood disorders.
However, the study found an association, and cannot prove that infections or autoimmune diseases are the cause of mood disorders. It's possible that other factors, such as stress or the experience of hospitalization, may explain the link, said Ian Gotlib, a professor of psychology at Stanford University, who was not involved in the study.
The study is published today (June 12) in the journal JAMA Psychiatry.
Infections and mood disorders
The study included people born in Denmark between 1945 and 1996 who were followed until the end of 2010.
During the study, more than 91,000 people visited a hospital for a mood disorder, including bipolar disorder or depression. Of these, about 32 percent visited hospitals for an infection before their mood disorder, and 5 percent visited the hospital for an autoimmune disease before their mood disorder.
The risk of a mood disorder was greatest in the first year following an infection or autoimmune disease.
People who visited a hospital for both an infection and an autoimmune disease had a greater risk of developing a mood disorder than those who visited a hospital for either of the two conditions alone. This may indicate the two conditions interact to increase the risk of mood disorder, the researchers said.
Because the study looked at information from only people hospitalized with infections, autoimmune disorders and mood disorders, it’s not clear whether the findings may apply to people with less severe infections, or mood disorders.
What's the cause?
Gotlib called the study "impressive" and said it raises important questions. Previous studies have shown that people with depression have lower numbers of T cells (a type of immune cell), and are at increased risk for autoimmune diseases, Gotlib said.
But there are also many other risk factors for mood disorders that were not taken into account in this study, such as smoking and socioeconomic status, Gotlib said. Future studies should attempt to untangle whether infections are really the cause of mood disorders, or if the two just happen to occur together.
In addition, studies should investigate how, on a biological level, infections and autoimmune diseases might affect the brain to cause mood disorders, Gotlib said.