Thirty years ago, a professor at the Harvard School of Public Health published a study in a prestigious medical journal purporting to show that drinking coffee increased a person's risk of pancreatic cancer. When asked how his results had influenced his own habits, he responded that he had stopped drinking coffee. The following day a professor of biostatistics set up a Mr. Coffee in the departmental offices, indicating what he thought of his colleague's study.
I mention this because last week a committee of the International Agency for Research on Cancer, a branch of the World Health Organization, announced that it would classify cellphone use as a "possible carcinogen," putting it in a category with 240 other exposures, including coffee and the pesticide DDT. Despite decades of research, neither of these exposures has turned out to be a carcinogen in humans.
Although the report from the committee has not yet been published, we know that the WHO based its conclusion largely on the 13-country Interphone study, which provoked a large degree of confusion when published a year ago.
A number of points can help put the perplexing anxiety about the potentially dire consequences of using a cellphone in perspective. First, brain tumors are extremely rare, and their incidence has changed little in most advanced industrial countries over the past two decades. In Scandinavia, which has excellent registration of all cancer cases and where cellphone use was widespread early on, there is no evidence of an increase in different types of brain tumor.
Second, cellphone technology makes use of radio frequency energy, which is millions of times less powerful than ionizing radiation, such as X-rays and gamma rays that can damage DNA and other molecules in a cell and potentially initiate cancer. There is no known mechanism whereby radio frequency energy can induce or promote cancer.
Because of the rarity of brain tumors, they are usually studied using the case-control approach, in which cases of the disease of interest are identified after diagnosis, and a comparison group is assembled, composed of people without the disease who can serve as controls. Both groups are then questioned about their use of cellphones and other factors of interest. A major weakness of this type of study is that a person's memory may be inaccurate and, even more serious, people with brain tumors might answer questions about their exposure differently from the healthy people serving as controls, leading to biased results.
The Interphone study enrolled more than 5,000 cases of people with brain tumors and nearly 6,000 controls. The main findings were that overall, regular users of mobile phones had significantly reduced risks for glioma and meningioma, the two most common types of brain tumor. Only in the small group of users whose reported cumulative call time was 1,640 hours or more was there a modest increase in risk of glioma — but not of meningioma.
The results of this study were baffling, even to the authors, and they went to great lengths to caution against giving a causal interpretation to this result. So, it appears that International Agency for Research on Cancer is putting more weight on this result than the authors.
A reading of the Interphone paper as well as a judicious 2009 review of the epidemiology on this question by the International Commission for Non-Ionizing Radiation Protection makes one wonder what the WHO thought it would achieve by classifying cellphone use a "possible carcinogen."
We are faced with a paradox in our increasingly health-conscious society. It is simply a fact of life that research is going to be done on topics like cellphones. But we can never prove a negative or exclude the possibility of a miniscule risk, no matter how large the study. So even when expert bodies concede that there is no convincing evidence of a threat, we get impossibly vague advisories like the current one warning us of "possible carcinogenicity."
In an echo of the Harvard incident, Donald Berry, a professor of biostatistics at M.D. Anderson Cancer Center at the University of Texas, said "anything is a possible carcinogen." Speaking from his cellphone, he added, "This is not something I worry about and it will not in any way change how I use my cellphone."
Geoffrey Kabat is a cancer epidemiologist at the Albert Einstein College of Medicine and the author of "Hyping Health Risks: Environmental Hazards in Daily Life and the Science of Epidemiology."
I mention this because last week a committee of the International Agency for Research on Cancer, a branch of the World Health Organization, announced that it would classify cellphone use as a "possible carcinogen," putting it in a category with 240 other exposures, including coffee and the pesticide DDT. Despite decades of research, neither of these exposures has turned out to be a carcinogen in humans.
Although the report from the committee has not yet been published, we know that the WHO based its conclusion largely on the 13-country Interphone study, which provoked a large degree of confusion when published a year ago.
A number of points can help put the perplexing anxiety about the potentially dire consequences of using a cellphone in perspective. First, brain tumors are extremely rare, and their incidence has changed little in most advanced industrial countries over the past two decades. In Scandinavia, which has excellent registration of all cancer cases and where cellphone use was widespread early on, there is no evidence of an increase in different types of brain tumor.
Second, cellphone technology makes use of radio frequency energy, which is millions of times less powerful than ionizing radiation, such as X-rays and gamma rays that can damage DNA and other molecules in a cell and potentially initiate cancer. There is no known mechanism whereby radio frequency energy can induce or promote cancer.
Because of the rarity of brain tumors, they are usually studied using the case-control approach, in which cases of the disease of interest are identified after diagnosis, and a comparison group is assembled, composed of people without the disease who can serve as controls. Both groups are then questioned about their use of cellphones and other factors of interest. A major weakness of this type of study is that a person's memory may be inaccurate and, even more serious, people with brain tumors might answer questions about their exposure differently from the healthy people serving as controls, leading to biased results.
The Interphone study enrolled more than 5,000 cases of people with brain tumors and nearly 6,000 controls. The main findings were that overall, regular users of mobile phones had significantly reduced risks for glioma and meningioma, the two most common types of brain tumor. Only in the small group of users whose reported cumulative call time was 1,640 hours or more was there a modest increase in risk of glioma — but not of meningioma.
The results of this study were baffling, even to the authors, and they went to great lengths to caution against giving a causal interpretation to this result. So, it appears that International Agency for Research on Cancer is putting more weight on this result than the authors.
A reading of the Interphone paper as well as a judicious 2009 review of the epidemiology on this question by the International Commission for Non-Ionizing Radiation Protection makes one wonder what the WHO thought it would achieve by classifying cellphone use a "possible carcinogen."
We are faced with a paradox in our increasingly health-conscious society. It is simply a fact of life that research is going to be done on topics like cellphones. But we can never prove a negative or exclude the possibility of a miniscule risk, no matter how large the study. So even when expert bodies concede that there is no convincing evidence of a threat, we get impossibly vague advisories like the current one warning us of "possible carcinogenicity."
In an echo of the Harvard incident, Donald Berry, a professor of biostatistics at M.D. Anderson Cancer Center at the University of Texas, said "anything is a possible carcinogen." Speaking from his cellphone, he added, "This is not something I worry about and it will not in any way change how I use my cellphone."
Geoffrey Kabat is a cancer epidemiologist at the Albert Einstein College of Medicine and the author of "Hyping Health Risks: Environmental Hazards in Daily Life and the Science of Epidemiology."
