Radio frequency exposure in mobile phone users: implications for exposure assessment in epidemiological studies.

The majority of epidemiological studies investigating correlations between long-term low-level radiofrequency (RF) exposure from mobile phones and health endpoints have followed a case-control design, requiring reconstruction of individual RF exposure. To date, these have employed 'time of use' as an exposure surrogate from questionnaire information or billing records. The present study demonstrates such an approach may not account for variability in mobile phone transmit power, which can be roughly correlated with RF exposure. This variability exists (a) during a single call, (b) between separate calls, (c) between averaged values from individuals within a local study group and (d) between average values from groups in different geographical locations. The present data also suggest an age-related influence on talk time, as well as significant inaccuracy (45-60%) in recalling 'time of use'. Evolving technology and changing use behaviours may add additional complexities. Collectively, these data suggest efforts to identify dose response and statistical correlations between mobile phone use and subtle health endpoints may be significantly challenged.