Abstract
We investigated the risk of, prognosis of and symptoms of multiple sclerosis (MS) among all Danish residents who owned a mobile phone subscription before 1996. Using the Danish Multiple Sclerosis Registry and Civil Registration System, study subjects were followed up for MS through 2004. Poisson models were used to calculate incidence rate ratios (IRR, age range: 18–64 years) and mortality rate ratios (MRR, age range: 18+) and to compare presenting symptoms among subscribers and all non-subscribers. A total of 405 971 subscription holders accrued four million years of follow up, with men accounting for 86% of the observation time. Among subscription holding men, the IRR of MS was close to unity, overall as well as 13+ years after first subscription (IRR 1.02, 95% CI: 0.48–2.16). Among women, the IRR was 3.43 (95% CI: 0.86–13.72) 13+ years after first subscription, however, based on only two cases. Presenting symptoms of MS differed between subscribers and non-subscribers (p = 0.03), with slightly increased risk of diplopia in both genders (IRR: 1.38, 95% CI: 1.02–1.86), an increased risk of fatigue among women (IRR: 3.02, 95% CI: 1.45–6.28), and of optic neuritis among men (IRR: 1.38, 95% CI: 1.03–1.86). Overall the MRR was close to one (MRR: 0.91, 95%CI 0.70–1.19) among MS-patients with a subscription and although we observed some increased MRR estimates among women, these were based on small numbers. In conclusion, we found little evidence for a pronounced association between mobile phone use and risk of MS or mortality rate among MS patients. Symptoms of MS differed between subscribers and nonsubscribers for symptoms previously suggested to be associated with mobile phone use. This deserves further attention, as does the increased long-term risk of MS among female subscribers, although small numbers and lack of consistency between genders prevent causal interpretation.
Highlights
Usage of mobile phones has changed dramatically in the last two decades, with steeply increasing number of users and decreasing age at first use
Stratification of subscription holders by years since first subscription showed a slight overall increase in increased risk of fatigue among women (IRR) of multiple sclerosis (MS) among male subscribers of 10 to 20% in the period from 1–9 years after first subscription, there was no elevation in risk before or after that interval
Among women, elevated IRRs were seen in the first year after subscription (1.61; and beyond 10 years of subscription (2.08; 95%CI: 1.08–4.01, n = 9), whereas the risk estimates were close to one in the intervening period
Summary
Usage of mobile phones has changed dramatically in the last two decades, with steeply increasing number of users and decreasing age at first use. It is of interest that a Swedish research group has observed leakage of the blood brain barrier in rats exposed to 900 MHz field from a GSM phone [7,8,9,10]. Attempts to replicate these findings have, failed and the overall evidence remains controversial [11,12,13,14]. The results may have caused concern in MS patients as to whether mobile phones have an impact on their disease. A recent nationwide Danish cohort study examined the association between mobile phone use and risk of various CNS diseases based on information on mobile phone subscription status prior to 1996
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