Schüz J, Waldemar G, Olsen JH, Johansen C (2009) Risks for Central Nervous System Diseases among Mobile Phone Subscribers: A Danish Retrospective Cohort Study. PLoS ONE 4(2): e4389. doi:10.1371/journal.pone.0004389.

Radiofrequency electromagnetic fields (RF-EMF) emitted by mobile phone antennas can penetrate 4-6 cm into the human brain. Therefore, most research on the potential health effects of mobile phone use has focused on very localized effects of this exposure, such as brain tumors. However, effects on the central nervous system (CNS) are also possible.  Recent reviews of epidemiological studies found increased risks of Alzheimer disease and amyotrophic lateral sclerosis (ALS) but not of vascular dementia, epilepsy or Parkinson disease associated with occupational exposure to extremely low frequency EMFs.

To investigate hospitalization rates for CNS diseases among a cohort of Danish mobile phone subscribers compared to the general population.

The final cohort comprised of 420,095 private mobile phone subscribers in Denmark from 1982-1995. Through record linkage of cohort members with the Central Population Register, participants were followed from the date of the first subscription until the date of first hospital contact, date of death, date of emigration, or December 31, 2003, whichever came first. CNS events were defined as: Alzheimer disease, vascular dementia, other dementia, Parkinson disease, amyotrophic lateral sclerosis (ALS), multiple sclerosis, and epilepsy. Information on hospitalizations for migraine and vertigo were also obtained. A standardized hospitalization ratio (SHR) was calculated by comparing the number of hospital contacts observed within the cohort to those that would have been expected, given the general population rates of hospital contacts for these diseases.

Before 1982, the majority of phone subscribers (80%) were aged 30-59. In 1995, 62% of subscribers were between 18-29 years, 31% were between 30-59, and 7% were aged 60 or more. Women represented 15% of the cohort members. There was an overall small but statistically significant excess of hospital contacts for migraine and vertigo among cohort members (SHR 1.2 for men and women for migraine, 1.1 for men and 1.2 for women for vertigo). The SHR for Alzheimer disease, vascular dementia, other dementia, and Parkinson disease were statistically significantly decreased, indicating fewer hospital contacts among mobile phone users compared to the general population. There was no difference in number of hospital contacts for ALS and multiple sclerosis. There was a statistically significant decrease in SHR for epilepsy among men, but it was slightly increased among women.

Interpretation and Limitations
Headaches and dizziness are common self-reported symptoms associated with mobile phone use, but evidence that they are causally associated with exposure to RF-EMF is weak.  An increase in hospital contacts for migraine among cohort members compared to the general population could be due to higher average income among cohort members, which may make them more likely to visit a hospital for migraine symptoms instead of visiting a general practitioner. The reduced risk of hospital contact for all types of dementia, including Alzheimer disease, and for Parkinson disease, may be due to a decreased likelihood of becoming a mobile phone user in the earliest, non-symptomatic stages of the disease. Higher than average income, observed among cohort members, is related to a healthier lifestyle, which in turn is related to a lower risk of dementia, which could also explain the results. The strengths of this study are its size and long follow-up time. Its limitation is the use of subscriber information which is a crude measure of exposure. Mobile phone users whose subscriptions were not under their names were classified as unexposed while subscribers who didn’t actually use a phone were classified as exposed. Nonetheless, this misclassification would have only reduced the likelihood of finding an association between mobile phone subscription and hospital contact for CNS disorders. Also, those who subscribed after 1995 were included in the general population, which could also bias the results.

This study found an increase in hospital contact for migraine and vertigo among mobile phone subscribers, which deserves further attention. Potential biases may have caused the observed reduced rate of hospital contact for dementia and Parkinson disease among mobile phone subscribers.

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