Toxicology with laboratory animals (In Vivo Studies)

RESEARCH STUDIES

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02. Toxicology with laboratory animals (In Vivo Studies)
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Description
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Description

Description

Epidemiology is a scientific discipline that evaluates the effect of exposures on health. What is unique is that the studies are conducted on human beings in the real world, not in a laboratory or with other species. This type of study monitors groups of people who have had higher or lower EMF exposure to determine whether those with higher exposure have increased disease risk. Although it is challenging to determine whether exposure causes disease, epidemiology has the distinct advantage of studying real-world exposures in people, in contrast to laboratory research.

Epidemiology is a scientific discipline that evaluates the effect of exposures on health. What is unique is that the studies are conducted on human beings in the real world, not in a laboratory or with other species. It is also distinct in that researchers do not introduce the exposure or assign it randomly to some people and not others the way we do in an experiment, but instead the exposure is monitored along with health outcomes. Such studies determine whether those who are more highly exposed to a possible hazard have a greater risk of developing disease than those who are less exposed. For nonionizing radiation, we may ask whether those who live in homes near high tension power lines have a higher risk of developing leukemia than those who do not live inside homes near high tension power lines or whether those who use cell phones for extended periods of time have a higher risk of brain cancer than those who are less intensive users of cell phones.

Epidemiology has distinctive strengths, but also some limitations. By studying the experience of real people in the real world, the information from this research is directly relevant to the public health concerns since there is not a need to translate findings from laboratory animals or cell cultures to humans, or from extremely high exposures to more typical exposures. But there are corresponding challenges that come from studying humans in their natural environment. It can be difficult to accurately measure exposure and sometimes hard to find substantial enough variation in exposure. For example, if nearly everyone uses a cell phone, then we cannot find non-users for comparison to users and if we ask people to recall how much time they used their cell phone, their memory may not be accurate. Another major challenge is that the exposure we are interested in may be correlated with other exposures, so it is hard to separate one from the other. If those who live near cellular base stations more often reside in urban areas compared to those who live far from base stations, other characteristics of the urban environment such as air pollution may be correlated with potential radiofrequency radiation exposure so researchers need to make sure that they can distinguish between any effects of the two exposures.

There are two main types of epidemiology studies, cohort studies and case-control studies. Cohort studies are most like experiments, with groups of people identified who are exposed and unexposed (or more and less exposed) and then followed over time to find out how frequently each group develops disease. We compare the two groups with a relative risk, which is the risk of disease in the more exposed group divided by the risk of disease in the less exposed group, for example a relative risk of 2 means that higher exposure is associated with double the risk of lower exposure. The other major study type is a case-control study. In this design, we identify two groups, one that has developed a disease we are interested in and a healthy comparison group that is free of that disease. We then find out the exposure history of both of those groups in order to see whether those who got the disease have a history of more exposure than those who did not get the disease. The relative risk measure is called an odds ratio, which determines the odds of getting the disease among exposed versus unexposed persons.

Example Studies

Example Studies

Epidemiology study about human exposure to EMF

An example of an epidemiologic study is the INTERPHONE study that examined the association between cell phone use and brain cancer. A large group, 2708 people, with brain tumors were interviewed to determine their history of cell phone use and compared to 2972 people without brain tumors to see if people with brain tumors had more exposure to cell phones. History of cell phone use was similar for those with and without brain tumors, which suggests that cell phone use is not likely to be a cause of brain tumors, but some of the results raise concerns that leave the question unresolved.

Cohort study of cell phone use and brain tumors

An example of an epidemiologic study is the INTERPHONE study that examined the association between cell phone use and brain cancer. A large group, 2708 people, with brain tumors were interviewed to determine their history of cell phone use and compared to 2972 people without brain tumors to see if people with brain tumors had more exposure to cell phones. History of cell phone use was similar for those with and without brain tumors, which suggests that cell phone use is not likely to be a cause of brain tumors, but some of the results raise concerns that leave the question unresolved.

Case-control study of cell phone use and brain tumors

An example of an epidemiologic study is the INTERPHONE study that examined the association between cell phone use and brain cancer. A large group, 2708 people, with brain tumors were interviewed to determine their history of cell phone use and compared to 2972 people without brain tumors to see if people with brain tumors had more exposure to cell phones. History of cell phone use was similar for those with and without brain tumors, which suggests that cell phone use is not likely to be a cause of brain tumors, but some of the results raise concerns that leave the question unresolved.

Summary of findings

Summary of findings

People are concerned that cell phones may cause cancer or other health problems because the phones emit radiofrequency radiation and use is widespread. Brain tumors (including cancer and benign tumors) are the main worry because cell phones are held close to the head and because ionizing radiation, a higher energy form than non-ionizing radiation, is associated with some brain tumors. Several types of studies suggest that cell phone use does not cause brain tumors in humans. Studies of trends in new occurrence (incidence) of brain tumors have shown no increase over the three decades since cell phones have been widely used.

Regional, nationwide, and multi-country case-control studies of adult brain tumors have shown a few mixed findings, but no consistent associations between cell phone use and brain tumors. Two multi-country case-control studies of childhood/adolescent brain tumors reported no associations. Two large cohort studies with many years of follow-up of adult populations (in Denmark and the United Kingdom) found no associations. Other health effects including other adult cancers, children’s developmental problems, sleep disturbances, and reproductive problems have been considered, but studies of these health effects have been limited with no clear signals of increased risks.

References

References

  • Castaño-Vinyals G, Sadetzki S, Vermeulen R, et al. Wireless phone use in childhood and adolescence and neuroepithelial brain tumours: Results from the international MOBI-Kids study. Environ Int 2022;160:107069

  • Deltour I, Johansen C, Auvinen A, et al. Time trends in brain tumor incidence rates in Denmark, Finland, Norway, and Sweden, 1974-2003. J Natl Cancer Inst 2009;101(24):1721-1724.

  • Frei P, Poulsen AH, Johansen C, et al. Use of mobile phones and risk of brain tumours: Update of Danish cohort study. BMJ 2011;343:d6387.

  • Hardell L, Carlberg M, Hansson Mild K. Pooled analysis of case-control studies on malignant brain tumours and use of mobile and cordless phones including living and deceased subjects. Int J Oncol 2011;38(5):1465-1474.

  • International Agency for Research on Cancer. Non-ionizing radiation, part 2: radiofrequency electromagnetic fields. Lyon, France: IARC: 2013. IARC monographs on the evaluation of carcinogenic risks to humans, volume 102.

  • International Commission on Non-Ionizing Radiation Protection (ICNIRP). ICNIRP note: Critical evaluation of two radiofrequency electromagnetic field animal carcinogenicity studies published in 2018. Health Phys 2020;118(5):525-532.

  • The Interphone Study Group. Brain tumour risk in relation to mobile telephone use: Results of the INTERPHONE international case-control study. Int J Epidemiol 2010;39(3):675-694.

  • Little MP, Rajaraman P, Curtis RE, et al. Mobile phone use and glioma risk: Comparison of epidemiological study results with incidence trends in the United States. BMJ 2012;344:e1147.

  • Röösli M, Lagorio S, Schoemaker MJ et al. Brain and salivary gland tumors and mobile phone use: Evaluating the evidence from various epidemiological study designs. Ann Rev Publ Health 2019;40:221-238.

  • Schüz J, Pirie K, Reeves GK et al. Cellular telephone use and the risk of brain tumors: Update of the UK Million Women Study. J Natl Cancer Inst 2022;114(5):704-711.

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