Before reviewing the study in more detail, it's first necessary to consider the context – and, specifically, why mainstream media are prone to regular bouts of hand-wringing, in some cases scaremongering, about the possible adverse health effects of cell-phone use. It all boils down to some basic physics and biology. During a call, the cell-phone antenna emits RF radiation that can penetrate 4-6 cm into the user's brain. The localized nature of this RF-tissue interaction has led to concerns about the possible heightened risk of head and neck cancers. To date, though, the weight of epidemiological evidence suggests no increased risk for any tumour among cell-phone users with less than approximately 10 years of use.

The latest findings from the Danish cohort study reinforce that body of evidence, as well as extending the investigation of cancer risk to longer-term subscribers who have been using cell phones for more than 10 years. (Most studies to date have had comparatively few subjects who have used cell phones for 10 or more years.) In terms of the make-up of the Danish cohort, 357,553 were male and 62,542 were female. The mean time since first cell-phone subscription was 8.5 years and the median 8.0 years. Among the male subscribers, 304,349 (85.1%) had their subscriptions for less than 10 years; 42,549 (11.9%) for 10-14 years; and 10,655 (3.0%) for 15-21 years (maximum). Among the female subscribers, the corresponding values were 59,098 (94.5%), 3131 (5.0%) and 313 (0.5%) respectively.

Presenting the results of the study in the latest issue of the Journal of the National Cancer Institute (98 1707), Joachim Schüz of the Danish Institute of Cancer Epidemiology in Copenhagen, Denmark, and colleagues reported no increased risk of brain tumours, acoustic neuromas, salivary-gland tumours, eye tumours, leukaemias or overall cancer in this large sample of cell-phone subscribers. They also reported no increased risk of brain tumours and leukaemias among the 56,648 people whose cell-phone subscription was running for longer than 10 years. The authors concluded: "We found no evidence for an association between tumour risk and cellular telephone use among either short-term or long-term users. Moreover, the narrow confidence intervals provide evidence that any large association of risk of cancer and cellular telephone use can be excluded."

Even so, Schüz and his colleagues add a cautionary note based on the fact that there are few, if any, other nationwide cohort studies of cell-phone use. To plug this knowledge gap, the researchers are planning follow-up of the Danish cohort over time along with improved methods of assessing phone use. In the meantime, heavy-duty phone users should remember that it's good to talk, though silence can sometimes be golden (especially on a crowded train full of irritable commuters).

• For related discussion on this subject, see Mobile-phone safety: a hazard in itself, in which Jeroen van de Kamer argues that the strict limits on exposure to RF radiation – established to protect mobile-phone users – could actually do more harm than good when it comes to medical practice.