Soderqvist F, Carlberg M, Hardell L. Mobile and cordless telephones, serum transthyretin and the blood-cerebrospinal fluid barrier: a cross-sectional study. Environ Health. 2009 Apr 21 Ahead of print 8(1):19.
Exposure to radiofrequency fields (RF), such as those emitted from wireless phones, has been hypothesized to disrupt the blood-brain barrier (BBB). The blood-cerebrospinal fluid barrier (BCSFB) has received much less attention but may also be influenced by RF exposure. The BCSFB, like the BBB maintains brain homeostasis by separating the central nervous system from the blood stream. Blood serum levels of transthyretin (TTR), a protein found in the cerebrospinal fluid, could serve as a marker of BCSFB dysfunction.
To test whether long-term and short-term use of wireless phones was associated with serum concentrations of transthyretin.
A population registry was used to identify 1,000 potential subjects, 500 of each sex, aged 18-65 living in the municipality of Örebro, Sweden. Subjects received an information letter and were asked for a blood sample. Consenting subjects completed a questionnaire on employment history, use of wireless phones (mobile phones and digital enhanced cordless (DECT) telecommunications), other RF exposures (X-rays, radiation therapy), and health and lifestyle factors. Data collection took place between March and November, 2007. Blood samples were collected by a nurse at the Örebro University Hospital in the afternoon at the end of a working week. Normal transthyretin levels were those below the 3rd quartile of blood transthyretin concentration (0.31 g/L) and elevated levels were above this threshold. Wireless phone ‘non-users’ were subjects in the lowest quartile of overall use (<446 hours).
Of the 1,000 potential subjects, 314 agreed to participate and blood samples were available for 313. Participants were more likely to be female and older than non-participants. Transthyretin concentrations were higher among men and among those aged >47 years. Wireless phone users were 1.2 times (95% CI 0.6-2.4) more likely to have elevated transthyretin blood concentrations than non-users. Among mobile phone users, the highest risk of elevated transthyretin concentrations was among those who reported >10 years since first use (OR 1.5, 95% CI 0.7-3.3). When wireless phone use and serum transthyretin were considered as continuous variables, longer time since first wireless phone use was significantly (p=0.03) associated with increasing transthyretin TTR levels. When the results were stratified by gender, the significant association remained only for men. Short-term use of wireless phones (i.e. on the same day as leaving blood) did not increase the risk of having elevated versus not elevated transthyretin levels. However, when transthyretin values were considered as continuous, increasing time since use of wireless phones on the same day as leaving blood was associated with lower transthyretin values (p=0.06). This association was significant among women (p=0.03).
Interpretation and Limitations
The differences between men and women in the risk of elevated transthyretin levels associated with long-term wireless phone use might be explained by the higher transthyretin concentrations in men or by confounding by the use of hormones, which can up-regulate transthyretin synthesis. Transthyretin could not be measured in the cerebrospinal fluid directly, where damage to the BCSFB would have been best assessed, and serum concentrations had to be used as a surrogate marker. This study is also limited by the self-reported use of wireless phones and low response rate.
Increasing time since first use of wireless phones was associated with higher transthyretin levels. Higher transthyretin concentrations were seen in women with the shortest time between wireless phone use on the day blood was drawn and leaving a blood sample.