Recruitment of participants is based on all the following criteria, with no exceptions: female, living in Galicia, lactating, > 18 years old, volunteer participation, written informed consent and agreement to complete questionnaires about lactation, diet and other socio-demographic factors. Samples are collected by participants, and stored at the University of Santiago de Compostela under a coded system so that it is impossible to identify the donor from whom the sample comes, with the exception of the investigators. The project is adhered to the principles of the Helsinki Declaration. Participants are allowed to withdraw their consent at any moment of the study.