Prevalence of Headache among Handheld Cellular Telephone Users in Singapore: A Community Study

Environmental Health Perspectives, Nov, 2000 by Sin-Eng Chia, Hwee-Pin Chia, Jit-Seng Tan

We carried out a cross-sectional community study in Singapore to determine the prevalence of specific central nervous system (CNS) symptoms among handheld cellular telephone (HP) users compared to nonusers and to study the association of risk factors and CNS symptoms among HP users. A total of 808 men and women between 12 and 70 years of age, who lived in one community, were selected using one-stage cluster random sampling and responses to a structured questionnaire. The prevalence of HP users was 44.8%. Headache was the most prevalent symptom among HP users compared to non-HP users, with an adjusted prevalence rate ratio of 1.31 [95% confidence interval, 1.00-1.70]. There is a significant increase in the prevalence of headache with increasing duration of usage (in minutes per day). Prevalence of headache was reduced by more than 20% among those who used hand-free equipment for their cellular telephones as compared to those who never use the equipment. The use of HPs is not associated with a significant increase of CNS symptoms other than headache. Key words: cellular telephones, community, cross-sectional study, headaches. Environ Health Perspect 108:1059-1062 (2000). [Online 16 October 2000]

http://ehpnet1.niehs.nih.gov/docs/2000/108p1059-1062chia/abstract.html

The use of handheld cellular telephones (henceforth referred to as hand phone; HP) has been on the increase, with more and more individuals using HPs because of the convenience they offer over other modes of telecommunication. In Singapore, 4 out of 10 people own an HP. The market is largely dominated by the digital system (GSM). More than 80% of these HPs operate using the GSM 900 system, with another 12% using the GSM 1800 system; both are digital systems. In the digital system, the information is sent via pulse-modulated signals of frequency between 870 and 995 MHz. Within this frequency band, the wave is nonionizing.

Present knowledge of health effects on humans from this frequency band (870-995 MHz) is limited. Most researchers have reported the effects of radio-frequency radiation (RFR) on laboratory animals and cell cultures. Salford et al. (1) demonstrated that low levels of RFR can alter the blood-brain barrier in mice, and Hocking (2) has preliminary evidence of an effect by 830 MHz RFR on endothelial cell cultures. Lai et al. (3) reported that rats exposed to low levels of RFR have impaired learning and an associated change in acetylcholine receptor levels.

In humans, health symptoms have previously been described in connection with work-related exposure to low-level radio frequency fields or microwaves (4). People who have been occupationally exposed to these fields have complained of heavy feelings in the head, headaches, fatigue, and poor memory more often than controls (4). The number of anecdotal reports of symptoms experienced by HP users around the world is increasing. These symptoms include headaches, dizziness, warmth or tingling around the ear and face, and difficulties concentrating (2,5,6).

In a case series of 40 mobile phone users, Hocking (2) reported that 35 of them complained of cranial symptoms such as a burning feeling or dull ache, mainly in the temporal, occipital, and auricular areas; 11 reported visual effects; 15 reported nausea, dizziness, or "fuzziness" in the head that made thinking difficult; and 75% of the cases were associated with digital mobile phones. A large cross-sectional, Swedish-Norwegian epidemiologic study was conducted by Mild et al. (6) in 1995. The authors studied 8,879 GSM phone users and 8,113 NMT (analog system operating at 900 MHz). Generally, the GSM phones have a lower power output than the NMT phones. The researchers' main hypothesis was that GSM users experience more symptoms than NMT users. Mild et al. (6) reported that among GSM users there were significant statistical associations between calling time and number of calls per day and the occurrence of warmth behind, around, and on the ear; headache; fatigue; burning facial skin sensation; and dizziness.

There are shortcomings in both studies. Hocking's study (2) is only a case series and does not point to an association between mobile phone use and symptoms. In addition, the study have been biased given that "respondents were recruited by a notice in a medical journal in 1996 which led to some media publicity" (2). Although the study by Mild et al. (6) is a large cross-sectional study, it involved subjects who used GSM or NMT HPs (6). There was no comparison between the HP users and non-HP users with regard to health symptoms. Mild et al. (6) stated that

   The media has focused on possible health effects caused by microwaves
   emitted by mobile phones (MP). It is possible that fear or awareness might
   cause MP users to report more symptoms than people not using MPs even if
   the prevalence of symptoms were equal.

This reasoning is valid; thus they were only able to compare the symptoms of two types of HP users, that is, one involving the use of the analog system (NMT) and the other the digital system (GSM). Both of these studies (2,6) are not community based in spite of the common use of HPs in the community.