The effect of long-term radiofrequency exposure on cognition in human observational studies: A protocol for a systematic review

Background: The long term effects of exposure to radiofrequency (RF) electromagnetic fields (EMF) for frequencies from 100 kHz to 300 GHz on cognitive performance are best assessed using observational studies. In recent years, the use of mobile (cell) phones has been the main source of RF EMF exposure to the brain, although other sources of exposure may be significant. Cognitive function includes various mental and psychological abilities, which can be measured in a range of domains, such as learning, memory, reasoning, problem solving, decision making and attention. Although effects on cognitive function may be most evident later in life, in the experimental setting acute and immediate effects can only be studied. Observational studies are needed when effects are observed after months or years following short or long-term exposure. The importance of the effects of exposure on children has also been recently identified. Objectives: To assess the long-term effects of RF EMF local and whole-body exposure compared to no or a lower level of exposure on indicators of cognition, including complex attention, executive function, learning and memory, perceptual motor ability and social cognition, but excluding cognitive effects caused by neurodegenerative diseases or neurodevelopmental disorders, and to assess if there is evidence of a dose response relationship. Study eligibility and criteria: We will include observational studies that have evaluated cognitive effects of RF energy including a comparator group with a different level of exposure. Studies must report at least one validated measure of cognitive function, including global or domain specific measures, or cognitive impairment, with a minimum follow-up of 6 months. Cohort or case-control studies published in the peer review literature in any language are eligible. We will exclude cross-sectional studies and any that only report brain structure or biomarkers. Study appraisal and synthesis method: We will conduct searches of PubMed, Embase, PsycINFO and the EMFPortal. At least two authors will independently screen the titles/abstracts of all records, with any conflicts resolved by a third reviewer. Full-text screening will also be conducted independently by two authors with conflicts resolved by consensus. Data will be extracted from the studies included, such as identifiers and characteristics of the study design, exposure and comparator groups, participants, outcomes assessed and results. Risk of bias will be assessed with the Office of Health Assessment and Translation (OHAT) tool. We will conduct a meta-analysis of similar studies with a random effects model in STATA or similar software, if two or more studies are available for a given exposure-outcome combination. Confidence in the body evidence will be judged using GRADE methods as adapted by OHAT for reviews of environmental exposures.