Map of the Reggio Emilia municipality, northern Italy (extension 231.6 ...

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Scientific diagram: Map of the Reggio Emilia municipality, northern Italy (extension 231.6 km2, population 169223 at Sep...

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Vinceti et al. Environmental Health 2010, 9:77 http://www.ehjournal.net/content/9/1/77

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The relation between amyotrophic lateral sclerosis and inorganic selenium in drinking water: a population-based case-control study Marco Vinceti1*, Francesca Bonvicini1,2, Kenneth J Rothman3,4, Luciano Vescovi5, Feiyue Wang6

Abstract Background: A community in northern Italy was previously reported to have an excess incidence of amyotrophic lateral sclerosis among residents exposed to high levels of inorganic selenium in their drinking water. Methods: To assess the extent to which such association persisted in the decade following its initial observation, we conducted a population-based case-control study encompassing forty-one newly-diagnosed cases of amyotrophic lateral sclerosis and eighty-two age- and sex-matched controls. We measured long-term intake of inorganic selenium along with other potentially neurotoxic trace elements. Results: We found that consumption of drinking water containing ≥ 1 μg/l of inorganic selenium was associated with a relative risk for amyotrophic lateral sclerosis of 5.4 (95% confidence interval 1.1-26) after adjustment for confounding factors. Greater amounts of cumulative inorganic selenium intake were associated with progressively increasing effects, with a relative risk of 2.1 (95% confidence interval 0.5-9.1) for intermediate levels of cumulative intake and 6.4 (95% confidence interval 1.3-31) for high intake. Conclusion: Based on these results, coupled with other epidemiologic data and with findings from animal studies that show specific toxicity of the trace element on motor neurons, we hypothesize that dietary intake of inorganic selenium through drinking water increases the risk for amyotrophic lateral sclerosis.

Background Amyotrophic lateral sclerosis (ALS), a severe neurodegenerative disease, has no established environmental risk factors [1]. Although some studies report that its incidence has been stable, others report changes in incidence over time and geographic variation in occurrence [2,3]. Some environmental factors, particularly neurotoxic elements and pesticides, have been implicated by some investigations [4-6]. Two epidemiologic studies [7,8] have focused on the possible role of selenium (Se), an element of nutritional and toxicological interest [9]. Environmental Se exists in organic and inorganic forms, with the organic forms being virtually the only ones found in food [10]. Dietary Se intake in Italy has been estimated to be about 50 μg/d per person [11]. Inorganic forms of Se are found more commonly in drinking * Correspondence: [email protected] 1 CREAGEN - Environmental, Genetic and Nutritional Epidemiology Research Center, University of Modena and Reggio Emilia, Reggio Emilia, Italy Full list of author information is available at the end of the article

water or some occupational settings. A safe intake range for Se is currently under debate [9]. Recent observations imply that it might be much lower than the value that has been assumed [12,13]. In an earlier study, Vinceti et al. reported that the population of Reggio Emilia, northern Italy, where some inhabitants consumed drinking water with unusually high Se content, experienced excess ALS incidence during the period 1986-1994, with a relative risk of 4.2 compared with those consuming water with lower levels of Se [8]. The present study was undertaken to determine whether this association has persisted during the years since the earlier report.

Methods We conducted a population-based case-control study in the Reggio Emilia municipality, measuring Se levels in the drinking water of cases and matched controls and using interviews to collect other relevant data from study subjects or their proxies. Eligible cases were all

© 2010 Vinceti et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Vinceti et al. Environmental Health 2010, 9:77 http://www.ehjournal.net/content/9/1/77

Reggio Emilia residents who received a first-time diagnosis of ALS during the years 1995 to 2006, provided that they had been residents of Reggio Emilia for at least six months. Cases were identified using a methodological approach that has already been described in detail [3]. In collaboration with expert neurologists, we reviewed the Hospital Discharges Register of the Emilia Romagna Region for both inpatients and outpatients of public and private hospitals from 1995 to 2006, as well as death certificates from 1996 through 2007, and all prescriptions for riluzole, the only drug specific for ALS. Only patients fulfilling the El Escorial revised diagnostic criteria [14] for probable or definite ALS, and residing in the Reggio Emilia municipality at the time of diagnosis, were included as cases. We selected controls from the general population of Reggio Emilia, identifiable through annual directories of residents made available by the General Registry Office of the region. Using the calendar-year specific file of municipal residents corresponding to the year of diagnosis for each case, we randomly selected two controls matched to the case for year of birth and sex, using the sample command of Stata statistical software (version 10.1, Stata Corp., College Station, TX 2009). We contacted all cases and controls by phone or visiting them directly, and we asked permission to administer a questionnaire at the subject’s home, at the University office in Reggio Emilia, or in a few instances by telephone. All cases or their relatives were contacted jointly by two of the coauthors (M.V. and F.B.) and all but one agreed to participate. For deceased cases (39/41) and controls (13/82), we asked permission to administer the questionnaire to the closest available relative, in most cases the marital partner or a son or daughter. All participants were able to provide detailed information about the subject’s drinking water consumption and provided well water samples if applicable. We were unable to enroll eleven of the initially sampled eighty-two controls: one could not be contacted, six refused to participate, and four could not provide samples of well-water owing to the collapse of the well coupled with absence of other wells in the vicinity. For these eleven subjects, we resampled the population to obtain substitute controls. The questionnaire we administered was designed to collect information about residential history and sources of domestic drinking water during the thirty-five years before diagnosis for cases, and for the corresponding period for the matched controls. The questionnaire also asked about consumption of dietary supplements (types and duration), family history of ALS in first-degree relatives, occupational history, life-style factors (smoking habits, coffee and alcohol consumption), and history of trauma sufficient to result in admission to a hospital.

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We also checked residential history information reported by the subject against the files of the Municipal Registry Office. When the latter data were inconsistent with those recalled by the subjects during the interview, we contacted the subject to resolve the discrepancy. For study participants who reported consuming well water, we obtained details, including year starting, year ending, and estimated percentage of total water consumed. We also sought permission to sample this water, when it was available. If subjects were no longer residing in the house that had the well, we contacted those currently living at that address and we asked their permission to sample the water. For three study subjects (all controls), the original well was not accessible in 2009 because it had collapsed, but after contacting a neighboring family we were able to get a sample of water from a nearby well. We ascertained that the well depth from the neighboring well was comparable (± 5 m) with that of the subject’s original well and that the distance between the two wells was
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