Diana Zuckerman, PhD, Brandel France de Bravo, MPH, Dana Casciotti, PhD, Megan Cole, MPH, Krista Brooks, BS
Updated November 2011
You’ve probably heard about news stories claiming that “cell phones are dangerous” and others claiming that “cell phones have been proven safe.” It’s hard to know what to believe-especially when we’ve grown so dependent upon these convenient communication devices.
Should We Be Worried?
Have you ever read the fine print in your cell phone manual? All manuals say not to hold the phone next to your ear, but how many of us actually talk on cell phones while holding them an inch away?
In July 2008, Dr. Ronald Herberman, Director of the University of Pittsburgh Cancer Institute, made quite a stir in the media when his warning to staff was made public: he told his employees that cell phone radiation may present more of a health risk than we had thought. He advised that rather than wait for definitive studies, we should immediately curb our cell phone use, and especially cell phone use by children.[1]
The extensive use of cell phones is a relatively recent phenomenon, and since cancers usually take at least 10-20 years to develop, it will be years before research is likely to conclude whether cell phones cause cancer or not.
The International Agency for Research on Cancer (IARC), which is part of the World Health Organization (WHO), recently tackled the subject. They brought together 31 scientists, including scientists with financial ties to cell phone companies, to review all relevant data on radiation from wireless handheld devices such as cell phones. This type of radiation is known as Radio Frequency-Electromagnetic Radiation (RF-EMR) and sometimes call microwave radiation. The IARC concluded that the evidence suggests this radiation is “possibly carcinogenic to humans,” and that there wasn’t enough research evidence to conclude that cell phones are dangerous or that they are safe. The Chairman of the Working Group, Dr. Jonathan Samet, stated that “we need to keep a close watch for a link between cell phones and cancer risk.”[2]
In addition to possibly increasing our risk of cancer, new research shows that cell phone radiation may have other negative health effects, including harming sperm, reducing male fertility, harming your quality of sleep, worsening migraines, and even changing the behavior of the cells inside your body.
A laboratory study lead by Dr. Nora Volkow, the director of the National Institute on Drug Abuse, and published in the February 2011 issue of the Journal of the American Medical Association, shows that the radiation from a cell phone stimulates brain activity in the area of the brain closest to the phone’s antenna, even when the sound from the cell phone is on mute.[3] The scientists measured changes in brain glucose metabolism, which is an indicator of brain activity, by placing cell phones on the left and right ears of 47 healthy people. Brain activity, and therefore glucose metabolism, would be expected to increase while talking or listening, which is why the study evaluated glucose metabolism when the phone was off (on both ears) and then when the phone was on and transmitting a call but on mute (on the right ear). The health implications of the study: are unknown: would the spikes in brain activity be harmful or might they be beneficial? What is important about the study is that it proves that non-ionizing radiation-energy waves commonly thought to be too weak to damage DNA and cause cancer-does have an effect on the brain.
What Does Research Tell Us about Cell Phones and Tumors?
Three years ago, a review of 18 studies of cell phones and brain tumors, published in Occupational and Environmental Medicine by Lennart Hardell and his colleagues, concluded that studies of individuals using cell phones for more than 10 years “give a consistent pattern of an increased risk for acoustic neuroma and glioma,” with the risk being highest for a tumor on the same side of the head that the phone is used.[4] Gliomas are the most common cancerous brain tumor, and the majority of gliomas are malignant (and usually fatal). Acoustic neuromas are benign tumors of the acoustic nerve that can cause deafness. The studies were conducted in the United States, Sweden, Finland, the U.K., Germany, and Japan.
Meanwhile, cell phone companies continue to insist that the evidence shows that their cell phones are safe. Cell phone companies tend to focus on the studies they funded themselves and that draw conclusions that will keep their business booming. A good example is a study by Schuz and colleagues at the Danish Cancer Society and International Epidemiology Institute, but funded by cell phone companies.[5] That study included more than 420,000 Danes who first started a cell phone subscription between 1982 and 1995, and were followed through 2002 to determine if they were diagnosed with acoustic neuroma, gliomas, or other head cancers. That sounds impressive, but while the study describes that it followed cell phone users “for up to 21 years,” the average subscription was started only 8.5 years before the study was completed, and only 3% had started using cell phones 15 or more years before the data were analyzed. Therefore, this study did not evaluate people using cell phones for a long enough period to determine if cell phone use causes cancer.
There were other problems with that study as well. Individuals with corporate accounts were excluded from the sample, which is also a shortcoming because they were the early adopters and heaviest users of cell phones. And, while that study reported no increased likelihood of brain cancers for those who used cell phones for more than 10 years, 10 years is not very long and cell phone usage in the 1980s and 1990s was much less frequent than it is today. Another shortcoming of that study is that the researchers did not evaluate on which side of the head the phone was used and whether the tumor was on the same side, which was a key variable predicting tumors in other studies.
The Latest, Largest Studies Give Mixed Results and Cause for Concern
In 2009, Australian neurosurgeon, Vini Khurana, together with Lennart Hardell and other scientists, conducted a meta-analysis of 11 studies published in peer-reviewed journals on long-term cell phone use and the risk of developing brain tumors. To be included in this meta-analysis, the studies had to follow cell phone users for at least ten years and document on which side of the head participants held their phones. Three studies did not meet the second of the two criteria and were therefore excluded. The authors concluded, in their article in Surgical Neurology, that using a cell phone for ten or more years “approximately doubles the risk of being diagnosed with a brain tumor” on the side of the head where the cell phone user holds the phone.[6]
The Interphone Project
More than half of the studies in Khurana and Hardell’s meta-analysis were from the Interphone Project, which is an international effort to investigate possible tumor risks associated with the use of mobile phones in 13 countries. The U.S. is not participating in that research. A shortcoming of the research is that Interphone studies define “regular cell phone use” as at least one call per week for at least 6 months, and long-term use is defined as at least one call each week for at least 6 years. Obviously, this is much lower usage than is typical today. The Interphone Project is funded by international organizations (World Health Organization, European Commission), cell phone companies, and with taxpayer money from participating countries.
The Interphone project has been underway for more than ten years and has cost more than $30 million. Results were repeatedly delayed due to conflicts over how to interpret the research and changes in leadership. In May 2010, new Interphone study results were finally released, with findings about longer-term use of cell phones. However, the results were unclear, concluding that “the possible effects of long-term heavy use of mobile phones require further investigation.” No increase in risk for brain tumors was seen for those who regularly used cell phones. In fact, overall, people who used cell phones actually were less likely to develop a brain tumor – but remember that regular use was defined as at least one call each week for 6 months. In contrast,people with the greatest use of cell phones (a total of 1640 hours or more over a 10 year period-about 27 minutes per day) increased their risk of glioma by 40%, compared to people who did not use a cell phone regularly.[7]
Controversies on Cell Phone Research Results
Underlying the controversy about cell phone radiation is the belief by most physicists that cell phone radiation could not possibly cause cancer. Although epidemiological research seems to suggest otherwise, that is undermined by other factors: cancer takes a very long time to develop, cell phone technology and frequency of usage has changed dramatically, and any link between cancer and cell phones could possibly be caused by unknown exposures or traits. For these and other reasons, IARC found most of the data to be inconclusive, including the Interphone study. Despite the increase in brain tumor risk for people with the highest cell phone use, the Interphone researchers stated that this finding could be due to biases and errors in the data, making their results were inconclusive. For example, the Interphone analysis questioned whether individuals diagnosed with brain cancer would tend to recall higher cell phone usage because of media attention to the risk of cell phones, or mistakenly recall that they used the phone on the side of their head where the tumor was found. However, numerous other researchers questioned the way in which the Interphone data were calculated, saying it underestimated risk. In addition, several researchers point out that people tend to hold a cell phone with the same hand almost all the time, and therefore would consistently use the phone on that side of their head.
After evaluating the size of potential biases in the Interphone analysis, Morgan, Kundi, and Carlberg used a “correction factor” to adjust these risks and concluded that the brain tumor risk increased significantly with greater cell phone use.[8] For example, according to the original Interphone calculation, a 2008 study led by Hepworth and colleagues showed that regular cell phone use for 10 years or more increased a person’s risk of glioma by 24% on the side of the head where the cell phone is held. When the risk calculations were corrected, the risk of glioma increased to 55%, a statistically significant increase, which means that it is unlikely to have occurred by chance. Similarly, a 2007 Interphone study by Anna Lahkola and colleagues showed that 5 to 9 years of cell phone use increased the risk of glioma by a non-significant 10% on the side of the head where the cell phone was used, but this increased to a statistically significant 38% increased risk when the risk calculations were redone.[9]
Most important, there is an inevitable problem with any studies conducted so far: cancer usually takes 15-20 years to develop. For example, most smokers start smoking in their teens, but even heavy smokers are rarely diagnosed with lung cancer until they are in their 40s or 50s. In fact, two out of every three cases of lung cancer are diagnosed in people 65 or older. This means that any cancer risk from cell phone use is likely to be difficult to measure until at least 10-20 years from now.
On the other hand, 10 or 20 years from now it may be difficult to study people who don’t use cell phones, in comparison to those that do. And, even the Interphone studies may have underestimated the brain tumor risk because of problems with their control group-the people who did not use cell phones or used them very infrequently. Even if these people did not use cell phones, many did use cordless phones in their homes and offices. Studies by Hardell have shown that use of a cordless phone increases the risk of certain types of tumors on the same side of the head almost as much as cell phone use. This is because cordless phones, unlike traditional land line phones, emit radiofrequency radiation, and people tend to have longer conversations on their cordless phones than they do on their cell phones.[10], [11], [12]
In a July 2010 study, National Cancer Institute researchers tested whether brain cancer rates increased in the years after cell phone use increased.[13] Data from 1992 to 2006 showed an increase in frontal lobe cancer in 20 to 29 year old women over this period, although the same increase was not seen in men. However, for other parts of the brain exposed to radiation from cell phones (the temporal lobe, parietal lobe, and cerebellum), there was no increase in cancer rates. Cancer takes a long time to develop and people have only recently begun to use cell phones regularly. The true effect of cell phones on brain cancer will be clearer in years to come, so continued research is greatly needed.
Beyond Brain Tumors: Other Health Concerns
While disagreements over the global Interphone results continue, several countries participating in the project, including Sweden, Denmark, France and Israel, have published their own results on brain tumors as well as other health problems.
Salivary gland tumors
Dr. Siegal Sadetzki and her colleagues at Tel Aviv University in Israel have found a link between salivary gland tumors and cell phones.[14] They reported that heavy cell phone users were more likely to have benign or malignant tumors of the salivary gland, compared to those who did not use cell phones. These findings became more worrisome when a July 2009 Hebrew University-Hadassah School of Dental Medicine study found a sharp rise in the number of cases of cancer of the parotid salivary gland in recent years. From 1980 to 2002, there were, on average, only 25 cases a year in Israel, but that nearly tripled to about 70 cases a year in the subsequent five years.[15]
Migraines and dizziness
A 2009 study linked long-term cell phone use to migraines and dizziness (known as vertigo). In this study of 420,095 Danish adults, when comparing long-term cell phone users with more recent cell phone users, the long-term users were 10-20% more likely to be hospitalized for migraines and vertigo.[16]
Sleep disturbance
A small 2007 study found that exposure to cell phone radiation before bed led to less sleep and poorer quality of sleep. People who were exposed to 884 MHz wireless signals for three hours before bed took six more minutes to reach deep sleep and spent eight fewer minutes in the deepest stage of sleep, in comparison to when they were not exposed to the cell phone signals.[17] These few minutes per day could contribute to sleep deprivation over several weeks and months.
Altered cell behavior
Exposure to cell phone radiation is now thought to alter the expression of certain proteins in the human body. In a 2008 Finnish study, females exposed to cell phone radiation that mimicked a one-hour phone call had significant changes in their levels of two different proteins after they were exposed: “one protein increased by 89%, the other decreased by 32%.”[18] This was the first study showing the molecular-level changes that take place in the human body, when exposed to cell phone radiation.
Altered sperm count and quality
A 2007 study by researchers at the Cleveland Clinic showed that use of cell phones decreases sperm quality in men.[19] They divided 361 men undergoing infertility evaluation into four groups according to the number of hours per day they spent talking on their cell phones. As the number of hours on the cell phone increased, the men’s sperm count, sperm motility (number of “swimming” sperm), viability (ability of sperm to survive), and normal morphology (normal shape of sperm) each decreased. Other studies have had similar findings. A Hungarian study following 231 men over a 13-month period showed that for heavy users of cell phones, sperm counts were, on average, 30% lower for heavy users of cell phones compared to men who did not have or use a cell phone.[20]
Similarly, in a 2009 study, Dr. John Aitken from the University of Newcastle in Australia found that as levels of cell phone radiation increase, the damage done to sperm also increases.[21] Dr. Aitken therefore recommends that men who would like to have children should avoid carrying cell phones in their pockets or anywhere below the waist. This is a dramatic development because the level of radiation for a phone that is in a pocket while not being used is much lower than the level of radiation during a phone conversation.
Risks for Children
A study published in 2008 in Physics in Medicine and Biology revealed that the brains of children under 8 absorb twice as much radiation from cell phones as adult brains.[22] A 2010 study published in Physics in Medicine and Biology noted that, “in general and on average, children suffer a higher exposure of their brain regions than adults.” This is because children have proportionally smaller heads and brains, yet receive the same levels of cell phone radiation as adults.[23]
None of the Interphone Project studies have looked at cell phone use begun in childhood or adolescence. Swedish researcher Lennart Hardell, however, has begun tracking the effects of early cell phone use. According to his research, people who begin using cell phones (and cordless landline phones) before the age of 20 are at an even higher risk of developing brain tumors than people who begin using these wireless phones as adults.[24], [25], [26]
Other researchers disagree. In July of 2011, the Journal of the National Cancer Institute published a study by Martin Röösli and others at the University of Basel suggesting that children and adolescents’ usage of mobile phones does not cause brain tumors. The study, called CEFALO, was a case-control study conducted in 4 locations: Denmark, Sweden, Norway and Switzerland. A case-control study means the researchers compared cell phone usage in people with brain tumors (cases) to those without brain tumors (controls). The two groups being compared are matched so that they are as similar as possible in every way (age, where they live, gender), except for cell phone use The researchers analyzed the amount of cell phone use among youth ages 7 to 19 diagnosed with a brain tumor between 2004 and 2008 and compared their use to cell phone use in the control group. They concluded that there was not significant evidence that cell phone use was linked to tumors.[27]
However, closer examination of the study reveals factors that possibly led to a misleading conclusion. First, the study was designed to examine the cell phone use of 550 cases, but only 352 were included. With such a small number of cases, the “power” to detect differences between cases and control is weakened. Therefore, it is less likely that researchers would observe a significant difference between the two groups, even if one truly exists. Second, there were inconsistencies between the case group and control group in estimating the duration of phone calls. While the cases overestimated the length of mobile phone calls by 52%, the controls’ average overestimation of duration of calls was 163%. As a result of this error, those that do not have tumors (controls) appear to have spent much more time on the phone than those with tumors. Again, this weakens the researchers’ ability to find a true association between cell phone use and cancer in the case group. Finally, the definition of “regular cell phone use” is problematic. According to Röösli’s study, regular cell phone use is defined as more than one phone call a week for six months. This means that someone who makes 2 short phone calls a week will be considered a regular user. This type of person will have much lower cell phone exposure than someone who makes calls every day. Grouping these two different types of users in the same category, again, undermines the ability to assess differences in risk based on low and high levels of use. When considering these factors, Röösli’s conclusions are not very convincing.
Different Types of Studies: How Can Researchers Get to the Bottom of This?
While there has been disagreement about how to interpret the CEFALO study’s data, there is a consensus among researchers, including Röösli and his colleagues, that retrospective studies present problems and that prospective studies are needed. Retrospective studies are ones that look back in time to study or measure risk, such as whether past cell phone use makes a person more likely to develop cancer or other health problems. But people may not remember their past behaviors accurately and researchers have no way to verify the information. Unless they use phone records, retrospective studies are also subject to “recall bias,” which means people with a disease might remember the past differently than people without a disease. In the case of cell phones, people with brain tumors may exaggerate their past cell phone use in an attempt to find an explanation for the inexplicable.
Prospective studies are ones that follow people over time and monitor the health problems that arise in the different groups during the study period. A prospective study of cell phone users would have to compare the health of infrequent users (controls) to heavy users (cases) as it becomes increasingly difficult to find people who never use cell phones.
Wireless technologies are proliferating daily, and different countries have different limits on radiation from wireless devices, which is why more and better designed research is urgently needed to determine safe levels of exposure. In the meantime, a number of experts are recommending that pregnant women and children limit their cell phone use.
A study of more than 13,000 Danish children published in Epidemiology suggests that cell phone exposure could affect children’s behavior.[28] The children in the study who were hyperactive or had emotional or behavioral problems, including trouble getting along with other kids, were much more likely to have mothers who used cell phones during pregnancy. The children’s problems, as reported by their mothers, were even more pronounced for children whose mothers used cell phones both during pregnancy and during their children’s first seven years of life. After accounting for other factors that could affect behavior, the children of these mothers were 80% more likely to have behavioral problems than children whose mothers rarely or didn’t use cell phones.
These results, based on a survey of Danish mothers whose children turned 7 in 2005 and 2006, are troubling but also somewhat difficult to interpret. Mothers using cell phones may be paying less attention to their children, causing them to “act out” in order to get attention. Research that is designed to provide more details of cell phone usage and other factors is needed to interpret the relationship between a mother’s cell phone use and her child’s behavior.
Precautions You Can Take
Scientists recognize that most people are not going to stop using cell phones. Since many studies suggest that there may be risks, experts like Ronald Herberman, Vini Khurana, and Lennart Hardell recommend that cell phone users take some precautions:
- Limit the number of calls you make.
- Limit the length of your calls.
- Use hands-free devices (wired cell phone headsets or wireless ones like Bluetooth).
- If you are not using a hands-free device, put the cell on “speaker phone” or hold the phone away from your ear.
- When speaking on your cell phone, alternate sides.
- Limit your cell phone use in rural areas or in any place where reception is poor. More radiation is emitted when you are farther from a cell phone tower.
- Shut off your phone or put it on “airplane mode” when possible. Airplane mode means email, Internet, and phone can’t be used, but you can listen to music or play games on the phone. This will reduce your exposure to radiation.
- Text message instead of talking (never while driving!).
- Check out how much radiation your phone emits by looking at its SAR (specific absorption rate), which is a measure of the amount of radiation absorbed by your body. When buying a new phone, try to select one with a lower SAR. A list of cell phones with the lowest SARs can be found here: http://www.ewg.org/cellphoneradiation/Get-a-Safer-Phone But remember, these SARs are based on a six foot tall, 200 pound man with an 11 pound head, and the levels are higher for smaller people
- Go over these guidelines with your children and limit their cell phone use.
In some cities and states, taking these precautions may soon be made easier. In March 2010, Maine legislators proposed a bill for placing warning labels on cell phones. This would be like warning labels on cigarettes, warning consumers about the increased risk of brain cancer from cell phone radiation. That effort was unsuccessful, but in June 2010, San Francisco voted to become the first city in the U.S. where cell phone stores must list each cell phone’s SAR. This radiation level will be listed next to the cell phone’s features and price.
Remember that cell phones emit radiation whenever they are on-even when they are not in use (although they emit even more during calls). So, avoid carrying the phone in your pocket or on your belt. You can keep it handy but store it away from your body-in a backpack, purse, or briefcase. If you have to carry it in your pocket, it’s best to turn it off until you need it. And if you use your cell phone as an alarm clock or sleep near it, make sure it is at least a few feet away.
In summary, although not enough time has passed for research to agree on the exact impact of cell phones on brain tumors and other health risks, the evidence so far suggests that we should be cautious. While hands free driving laws are resulting in greater use of ear pieces in cars, more and more people are opting not to pay for land lines and are relying exclusively on their cell phone. As a result, adults and children are holding cell phones to theirs ears for hours each day.
Should we be concerned? Remember that most published studies evaluated relatively infrequent cell phone usage and that research is inadequate to draw conclusions regarding safety. In the Interphone studies, “regular” cell phone usage was defined as at least one call per week for at least six months, which is a tiny fraction of typical usage today. The health impact of the long-term and frequent use of cell phones that is typical today could be substantially worse. And, if there is a cancer risk, we won’t see the effects of cell phone use on cancer rates for another 10-20 years. That is why it is important that researchers who do not have financial ties to cell phone companies continue long-term studies with more appropriate measures of high, medium, and low cell phone usage and include usage by children. In the meantime, you can play it safe and limit your and your children’s cell phone use.
[1] “Researcher warns of brain cancer risk from cellphones. July 24, 2008. The New York Times.http://www.nytimes.com/2008/07/24/technology/24iht-cellphone.4.14767955.html Complete warning from Herberman can be read at: http://www.upci.upmc.edu/news/pdf/The-Case-for-Precaution-in-Cell-Phone-Use.pdf
[3] Volkow, ND, Tomasi D, Wang G, Vaska P, Fowler JS, Telang F, Alexoff D, Logan J, Wong C. (2011) Effects of Cell Phone Radiofrequency Signal Exposure on Brain Glucose Metabolism. Journal of American Medical Association 305(8): 743-844.
[4] Hardell L, Carlberg M, Soderqvist F, Hansson Mild K, Morgan LL (2007). Long-term use of cellular phones and brain tumours: increased risk associated with use for = 10 years. Occupational and Environmental Medicine 64(9):626-632.
[5] Schuz J, Jacobsen R, Olsen JH, et al. (2006) Cellular telephone use and cancer risk: Update of a nationwide Danish cohort. Journal of the National Cancer Institute 98: 1707-1713.
[6] Khurana VG, Teo C, Kundi M, Hardell L, Carlberg M (2009) Cell phones and brain tumors: A review including the long-term epidemiologic data. Surgical Neurology 72(3): 205-214.
[7] Cardis E, Deltour I, Vrijheid M, Combalot E, Moissonnier M, Tardy H, et al (2010 May 17). Brain tumor risk in relation to mobile phone use: results of the INTERPHONE international case-study.International Journal of Epidemiology, 39(1): 675-694.
[8] Morgan LL, Kundi, M, & Carlberg M (2010 June). Re-evaluation of the Interphone Study: Application of a Correction Factor. Retrieved from http://electromagnetichealth.org/wp-content/uploads/2010/06/Poster_PDF_Final_6-10-10-1.pdf
[9] Lahkola A., et al. (2007). Mobile phone use and risk of glioma in 5 North European countries.
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[10] Hardell L, Carlberg M. (2009) Mobile phones, cordless phones and the risk of brain tumours.International Journal of Oncology.35(1):5-17.
[11] Hardell L, Carlberg M, and Hansson Mild K (2006). Pooled analysis of two case-control studies on use of cellular and cordless telephonesand the risk for malignant brain tumours diagnosed in 1997-2003. International Archives of Occupational and Environmental Health 79: 630-639.
[12] Hardell L, Carlberg M, and Hansson Mild K (2006). Pooled analysis of two case-control studies on the use of cellular and cordless telephones and the risk of benign brain tumours diagnosed during 1997-2003. International Journal of Oncology 28: 509-518, 2006.
[13] Inskip, PD, Hoover, RN, Devesa, SS (2010).Brain cancer incidence trends in relation to cellular telephone use in the United States, Neuro-Oncology 12: 1147-1151.
[14] Sadetzki S, CHetrit A, Jarus-Hakak A, et al. (2008) Cellular phone use and risk of benign and malignant parotid gland tumors-A nationwide case-control study. American Journal of Epidemiology167: 457-467.
[16] Schuz J, Waldemar G, Olsen JH, & Johansen C. (2009 Feb. 5). Risks for Central Nervous System Diseases among Mobile Phone Subscribers: A Danish Retrospective Cohort Study. PLoS ONE, 4(2): e4389 1-5. Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2632742/pdf/pone.0004389.pdf
[17] Arnetz BB et al (2007) The Effects of 884 MHz GSM Wireless Communication Signals on Self-reported Symptom and Sleep (EEG)- An Experimental Provocation Study PIERS Online 3(7):1148-1150
[20] Fejes I, Zavaczki Z, Szollosi J, Koloszar S, Daru J, Kovacs L, et a; (2005 Sept-Oct). Is there a relationship between cell phone use and semen quality? Arch Androl, 51(5): 385-393. Retrieved fromhttp://www.ncbi.nlm.nih.gov/pubmed/16087567
[22] Wiart J, Hadjem A, Wong MF, Bloch I. (2008) Analysis of RF exposure in the head tissues of children and adults. Physics in Medicine and Biology 53(13): 3681-3695 (15).
[23] Christ A, Gosselin MC, Christopoulou M, K’uhn S, & Kuster N. (2010 Jan.). Age dependent tissue-specific exposure of cell phone users. Physics in Medicine and Biology, 55: 1767-1783. Retrieved from http://iopscience.iop.org/0031-9155/55/7/001/pdf/0031-9155_55_7_001.pdf
[24] Hardell L, Carlberg M, Hansson Mild K. (2009) Epidemiological evidence for an association between use of wireless phones an tumor diseases. Pathophysiology 16 (2-3): 113-122.
[25] Volkow, ND, Tomasi D, Wang G, Vaska P, Fowler JS, Telang F, Alexoff D, Logan J, Wong C. (2011) Effects of Cell Phone Radiofrequency Signal Exposure on Brain Glucose Metabolism. Journal of American Medical Association 305(8): 743-844.
[26] Hardell L, Hansson Mild K, Carlberg M, Hallquist A. (2004) Cellular and cordless telephones and the association with brain tumours in different age group. Archives of Environmental Health 59 (3): 132-137.
[27] Aydin D, Feychting M, Röösli M, et al; (2011), Use and Brain Tumors in Children and Adolescents: A Multicenter Case-Control Study. Journal of the National Cancer Institute. 103(16): 1264-1276,
[28] Divan HA, Kheifets L, Obel C, Olsen J. (2008) Prenatal and Postnatal Exposure to Cell Phone Use and Behavioral Problems in Children. Epidemiology 19(4): 523-529.
http://center4research.org/healthy-living-prevention/products-with-health-risks/can-cell-phones-harm-our-health-2/
