This work was supported by a grant from the Fondo de Investigación Sanitaria (98/0462) and a grants from the Consejería de Salud del Principado de Asturias and Pfizer Laboratories. Recently, Sanofi Laboratories supported follow-up and fieldwork (done by Alicia Cobo, C.S. and J. A.) in 2010 and 2016 by grants. The funders had no role in study design, data collection and analysis,decision to publish, or preparation of the manuscript.