A proposed methodology to estimate the cumulative life-time UVB exposure using geographic information systems: An application to multiple sclerosis

Background: The cause of multiple sclerosis (MS) is unknown; multiple risk factors have been implicated, including environmental exposures, such as sunlight. Many studies have relied on latitude alone as a crude proxy for sunlight exposure. We aimed to develop a protocol allowing a more detailed estimate of cumulative ambient ultra-violet B (UVB) exposure at critical time-periods over a patient's life-course. Methods: 4010 definite MS patients with a 'movement history' from birth to the study end (2005) were selected from the University of British Columbia, Canada's MS Genetic database. Patient's place of resident from birth were tracked, each place being geocoded (latitude and longitude) and assigned a UVB value using the NASA Total Ozone Mapping Spectrometer (TOMS) dataset. Combined, these data allowed an estimated UVB value for each patient based on year and location. Results: Using this protocol, we provide a potentially more detailed cumulative UVB exposure for critical periods in a patients' life history based on their individual spatial migration through time. Conclusions: This protocol is intended to provide a framework for researchers to more accurately estimate UVB exposures for individuals over the course of their life history and may be useful for understanding etiology of MS and other chronic disease. (C) 2012 Elsevier B.V. All rights reserved.