| Spatial Analysis of the Relationship between Mortality from Cardiovascular and Cerebrovascular Disease and Drinking Water Hardness Juan Ferrándiz,1* Juan J. Abellán,1,2 Virgilio
Gómez-Rubio,1 Antonio López-Quílez,1 Pilar
Sanmartín,3Carlos Abellán,4 Miguel A. Martínez-Beneito,4 Inmaculada
Melchor,4 Hermelinda Vanaclocha,4 Óscar Zurriaga,4 Ferrán
Ballester,5 José M. Gil,5 Santiago Pérez-Hoyos,5 and
Ricardo Ocaña6 1Departamento d'Estadística i Investigació Operativa,
Universitat de València, Valencia, Spain; 2Instituto Valenciano
de Estadística, Generalitat Valenciana, Valencia, Spain; 3Departamento
de Matemática Aplicada y Estadística, Universidad Politécnica
de Cartagena, Cartagena, Spain; 4Departamento de Epidemiología,
Dirección General de Salud Pública, Generalitat Valenciana, Valencia,
Spain; 5Unidad de Epidemiología y Estadística, Escuela
Valenciana de Estudios para la Salud, Generalitat Valenciana, Valencia, Spain;
6Escuela Andaluza de Salud Pública, Consejería de
Salud, Junta de Andalucía, Granada, Spain Abstract
Previously published scientific papers have reported a negative correlation between drinking water hardness and cardiovascular mortality. Some ecologic and case-control studies suggest the protective effect of calcium and magnesium concentration in drinking water. In this article we present an analysis of this protective relationship in 538 municipalities of Comunidad Valenciana (Spain) from 1991-1998. We used the Spanish version of the Rapid Inquiry Facility (RIF) developed under the European Environment and Health Information System (EUROHEIS) research project. The strategy of analysis used in our study conforms to the exploratory nature of the RIF that is used as a tool to obtain quick and flexible insight into epidemiologic surveillance problems. This article describes the use of the RIF to explore possible associations between disease indicators and environmental factors. We used exposure analysis to assess the effect of both protective factors--calcium and magnesium--on mortality from cerebrovascular (ICD-9 430-438) and ischemic heart (ICD-9 410-414) diseases. This study provides statistical evidence of the relationship between mortality from cardiovascular diseases and hardness of drinking water. This relationship is stronger in cerebrovascular disease than in ischemic heart disease, is more pronounced for women than for men, and is more apparent with magnesium than with calcium concentration levels. Nevertheless, the protective nature of these two factors is not clearly established. Our results suggest the possibility of protectiveness but cannot be claimed as conclusive. The weak effects of these covariates make it difficult to separate them from the influence of socioeconomic and environmental factors. We have also performed disease mapping of standardized mortality ratios to detect clusters of municipalities with high risk. Further standardization by levels of calcium and magnesium in drinking water shows changes in the maps when we remove the effect of these covariates. Key words: environmental epidemiology, geographic information systems, hierarchical spatial models, relative risk, spatial smoothing. Environ Health Perspect 112:1037-1044 (2004) . doi:10.1289/ehp.6737 available via http://dx.doi.org/ [Online 15 April 2004]
This article is part of the mini-monograph "Health and Environment Information Systems for Exposure and Disease Mapping, and Risk Assessment." Address correspondence to A. López-Quílez, Dept. d'Estadística i Investigació Operativa, Universitat de València, Dr. Moliner 50, Burjassot E-46100, Spain. Telephone: 34 963543792. Fax: 34 963544735. E-mail: antonio.lopez@uv.es *The authors express their high regard and gratitude to Juan Ferrándiz, who died during the revision process of this article. Juan was the lead investigator of the Spanish EUROHEIS group and the lead investigator for all the people involved in the project. This research was funded partially by the Dirección General de Salud Pública, the Escuela Valenciana de Estudios para la Salud (grant IVESP99/066) , and the EUROHEIS project (grant SI2.329122, 2001CVG2-604) . The authors declare they have no competing financial interests. Received 12 September 2003 ; accepted 31 March 2004.
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